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1.what is OBD? 

On-Board Diagnostics - First Generation (OBD1)

With the exception of some 1994 and 1995 vehicles, most vehicles from 1982 to 1995 are equipped with some type of first generation On-Board Diagnostics.

Beginning in 1988, California’s Air Resources Board (CARB), and later the Environmental Protection Agency (EPA) required vehicle manufacturers to include a self-diagnostic program in their on-board computers. The program would be capable of identifying emissions-related faults in a system. The first generation of Onboard Diagnostics came to be known as OBD1.

OBD1 is a set of self-testing and diagnostic instructions programmed into the vehicle’s on-board computer. The programs are specifically designed to detect failures in the sensors, actuators, switches and wiring of the various vehicle emissions-related systems. If the computer detects a failure in any of these components or systems, it lights an indicator on the dashboard to alert the driver. The indicator lights only when an emissions-related problem is detected.

The computer also assigns a numeric code for each specific problem that it detects, and stores these codes in its memory for later retrieval. These codes can be retrieved from the computer’s memory with the use of a “Code Reader” or a “Scan Tool.”

On-Board Diagnostics - Second Generation (OBD2)

The OBD2 System is an enhancement of the OBD1 System.

In addition to performing all the functions of the OBD1 System, the OBD2 System has been enhanced with new Diagnostic Programs. These programs closely monitor the functions of various emissions-related components and systems (as well as other systems) and make this information readily available (with the proper equipment) to the technician for evaluation.

The California Air Resources Board (CARB) conducted studies on OBD1 equipped vehicles. The information that was gathered from these studies showed the following:

· A large number of vehicles had deteriorating or degraded emissions-related components. These components were causing an increase in emissions.

· Because OBD1 systems only detect failed components, the degraded components were not setting codes.

· Some emissions problems related to degraded components only occur when the vehicle is being driven under a load. The emission checks being conducted at the time were not performed under simulated driving conditions. As a result, a significant number of vehicles with degraded components were passing Emissions Tests.

· Codes, code definitions, diagnostic connectors, communication protocols and emissions terminology were different for each manufacturer. This caused confusion for the technicians working on different make and model vehicles.

To address the problems made evident by this study, CARB and the EPA passed new laws and standardization requirements. These laws required that vehicle manufacturers to equip their new vehicles with devices capable of meeting all of the new emissions standards and regulations. It was also decided that an enhanced on-board diagnostic system, capable of addressing all of these problems, was needed. This new system is known as “On-Board Diagnostics Generation Two (OBD2).” The primary objective of the OBD2 system is to comply with the latest regulations and emissions standards established by CARB and the EPA.

Objectives of OBD2

The Main Objectives of the OBD2 System are:

· To use a standardized Diagnostic Link Connector (DLC) in all vehicles. (Before OBD2, DLCs were of different shapes and sizes.)

· To standardize communication procedures and protocols between the diagnostic equipment (Scan Tools, Code Readers, etc.) and the vehicle’s on-board computer.

· To standardize the code numbers, code definitions and language used to describe faults. (Before OBD2, each vehicle manufacturer used their own code numbers, code definitions and language to describe the same faults.)

· To expand emissions-related system monitoring. This includes a set of computer run diagnostics called Monitors. Monitors perform diagnostics and testing to verify that all emissions-related components and/or systems are operating correctly and within the manufacturer’s specifications.

· To detect degraded and/or failed emissions-related components or systems that could cause tailpipe emissions to exceed by 1.5 times the Federal Test Procedure (FTP) standard.

· To expand the operation of the Malfunction Indicator Lamp (MIL) and command the MIL “on” when tailpipe emissions exceed the FTP standard by 1.5 times.

2,   Twhat is Data Link Connector ( DLC) ?

The Data Link Connector (DLC) provides the means of accessing and retrieving data from the vehicle’s on-board computer.

A Code Reader or Scan Tool is connected to the DLC to retrieve Diagnostic Trouble Codes (DTCs) and other enhanced data from the computer.

On OBD1 systems, the size, shape and location of the DLC varies between manufacturers. Typically, the DLC is located in the engine compartment, or under the left side of the dashboard.

OBD2 Systems use a standardized 16-pin DLC, as defined by SAE J1962/ISO 15031-3.

Several pins of the DLC are associated with specific features or functions used by OBD2-compliant control systems, and are required to be implemented uniformly by all vehicle manufacturers. These pins provide operating power (from the vehicle’s battery) to the Code Reader or Scan Tool, and provide the data paths for the various OBD2 “communication protocols.” The functions of the remaining “unassigned” pins manufacturer-defined, and can be used for such features and functions as Anti-Lock Brake Systems (ABS), Supplemental Restraint Systems (SRS), etc.

The OBD2 DLC connector pin assignments are:

While the DLC location varies between vehicle makes and models, it is usually located under the instrument panel (dash), within 16 inches of the steering column, on the driver’s side of most vehicles. It should be easily accessible from a kneeling position outside the vehicle with the door open.

3, what is Diagnostic Trouble Code (DTC) ? 

OVERVIEW

Diagnostic Trouble Codes (DTCs) are codes that identify a specific problem area.

Diagnostic Trouble Codes (DTCs) are numeric (OBD1 systems) or alpha-numeric (OBD2 systems) codes that are used to identify a problem that is present in any of the systems that are monitored by the vehicle’s on-board computer, also called the Powertrain Control Module (PCM).

DTCs are intended as a guide to the proper diagnostic/service procedures in the vehicle’s repair manual, and not as the sole source for repair. DO NOT replace parts based only on DTCs without first consulting the vehicle’s service manual for proper testing procedures for the associated system, circuit or component.

Malfunction Indicator Lamp (MIL)

Every vehicle’s instrument panel is equipped a Malfunction Indicator Light (also called a "Check Engine" light or "Service Engine Soon" light). When the vehicle's on-board computer detects a failure in an emissions-related component or system, the computer's internal diagnostic program
 

· Assigns a diagnostic trouble code (DTC) that points to the system (and subsystem) where the fault was found

· Saves the code in the computer's memory, and

· Lights the Malfunction Indicator Lamp (MIL).

OBD1 DIAGNOSTIC TROUBLE CODES

In OBD1 systems, Diagnostic Trouble Codes (DTCs) are manufacturer-specific. This means that each vehicle manufacturer developed its own set of DTCs, with meanings that apply only to vehicles made by that manufacturer. OBD1 DTCs are generally 2- or 3-digit numeric codes that represent a specific emission-related problem. OBD1 systems use the vehicle’s Malfunction Indicator Lamp ()MIL) to transmit DTCs from the vehicle’s Powertrain Control Module (PCM) by blinking “on” and “off.”

The method for counting the “blinks” varies between manufacturers as well. 

There are two types of fault codes possible in OBD1 systems:
 

· “Hard” Codes – “Hard” codes represent problems that are occurring now and cause the MIL to illuminate and remain on until the failure is repaired. A DTC is stored in the computer’s memory for later access.

· “Intermittent” Codes – “Intermittent” or “pending” codes may cause the MIL to “flicker” or to stay on until the intermittent malfunction goes away. However, the corresponding DTC will be stored in the computer’s memory for later access. If the malfunction does not reappear within a predetermined length of time (normally measured by ignition key start cycles), the computer automatically erases the DTC.

OBD2 DIAGNOSTIC TROUBLE CODES

A significant benefit in OBD2 systems is the standardization of Diagnostic Trouble Codes (DTCs). OBD2 DTCs can include both generic and manufacturer-specific codes.

Generic DTCs are codes that are used by all vehicle manufacturers. The definitions are the same, regardless of vehicle make or model. The standards for generic DTCs, as well as their definitions, are set by the Society of Automotive Engineers (ref. SAE J2012) and/or the International Standards Organization (ref. ISO 15031-6).

Manufacturer-specific DTCs are codes that are defined and controlled by the vehicle manufacturer. Vehicle manufacturers are not required to provide manufacturer-specific DTCs in order to comply with OBD2 emissions standards. However, manufacturers are free to expand beyond the required codes to make their systems easier to diagnose.

All OBD2 DTCs are made up of five alpha-numeric characters.

· The first character is a letter. It identifies the “main system” where the fault occurred.

P0201

B - Body
C - Chassis
P - Powertrain
U - Network
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• The second character is a numeric digit. It identified the “type” of code.
P0201
0 - Generic codes
1 - Manufacturer-specific codes
2 - Includes both Generic and Manufacturer-specific codes
3 - Includes both Generic and Manufacturer-specific codes
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• The third character is a numeric digit. It identifies the specific system or sub-system where the problem is located.
P0201
1 – Fuel and Air Metering
2 – Fuel and Air Metering (injector circuit malfunction only)
3- Ignition System or Misfire
4 – Auxiliary Emission Control System
5 – Vehicle Speed Control and Idle Control System
6 – Computer Output Circuits
7 – Transmission
8 – Transmission
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• The fourth and fifth characters are numeric digits. They identify the section of the system that is malfunctioning.
P0201
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- Body - Chassis - Powertrain - Network----------------• The second character is a numeric digit. It identified the “type” of code.P02010 - Generic codes1 - Manufacturer-specific codes2 - Includes both Generic and Manufacturer-specific codes3 - Includes both Generic and Manufacturer-specific codes----------------• The third character is a numeric digit. It identifies the specific system or sub-system where the problem is located.P02011 – Fuel and Air Metering2 – Fuel and Air Metering (injector circuit malfunction only)3- Ignition System or Misfire4 – Auxiliary Emission Control System5 – Vehicle Speed Control and Idle Control System6 – Computer Output Circuits7 – Transmission8 – Transmission----------------• The fourth and fifth characters are numeric digits. They identify the section of the system that is malfunctioning.P0201---------------- 

OBD2 systems do not use the MIL to transmit codes from the vehicle’s computer. Codes are retrieved from OBD2 systems using a Code Reader or Scan Tool.

There are two types of DTCs used for emissions-related faults in OBD2 systems: Type “A” and Type “B.” Type “A” codes are “One Trip” codes. Type “B” codes are usually “Two Trip” codes.
When a Type “A” DTC is found on the First Trip, the following events take place:
• The computer commands the MIL “on” when the failure is first found.
• If the failure causes a severe misfire that may cause damage to the catalytic converter, the MIL “flashes” once per second. The MIL continues to flash as long as the condition exists. If the condition that caused the MIL to flash is no longer present, the MIL will light steady “On.”
• A DTC is saved in the computer’s memory for later retrieval.
• A “Freeze Frame” of the conditions present in the engine or emission system when the MIL was commanded “On” is saved in the computer’s memory for later retrieval. This information shows fuel system status, engine load, coolant temperature, fuel trim value, MAP vacuum, engine RPM and DTC priority.
When a Type “B” DTC is found on the First Trip, the computer sets a Pending DTC, but the MIL is not commanded “On.” “Freeze Frame” data is not recorded at this time. The Pending DTC is saved in the computer’s memory for later retrieval.
• If the failure is found on the second consecutive Trip, the MIL is commanded “On” and “Freeze Frame” data is saved in the computer’s memory.
• If the failure is not found on the second Trip, the Pending DTC is erased from the computer’s memory.
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The MIL will remain “On” for both Type “A” and Type “B” codes until one of the following conditions occurs:
• If the conditions that caused the MIL to light are no longer present for the next three consecutive trips, the computer automatically turns the MIL “Off” if no other emissions-related faults are present. However, the DTCs remain in the computer’s memory for 40 warm-up cycles (80 warm-up cycles for fuel and misfire faults). The DTCs are automatically erased if the fault that caused them to be set is not detected again during that period.
• Misfire and fuel system faults require three trips with “similar conditions” before the MIL is turned “Off.” These are trips where the engine load, RPM and temperature are similar to the conditions present when the fault was first found.
After the MIL has been turned “Off,” DTCs, Freeze Frame data, and manufacturer-specific enhanced data stay in the computer’s memory. This data can only be retrieved by suing equipment such as a Scan Tool.
• Erasing the DTCs from the computer’s memory can also turn the MIL “Off.”
If a Code Reader or Scan Tool is used to erase DTCs from the computer’s memory, Freeze Frame data as well as other manufacturer-specific enhanced data is also erased.

4, about Communication Protocols you should know

A “communication protocol” is a means by which data is exchanged between the vehicle’s on-board computer and an external data retrieval device, such as a Code Reader or Scan Tool. The SAE has defined three distinct communication protocol “classifications,” based on the speed at which data transfer takes place:

· Class A – Supports data transfer speed of up to 10Kb/s

· Class B – Supports data transfer speeds of up to 100Kb/s

· Class C – Supports data transfer speeds of up to 1Mb/s

Currently, five communication protocols are defined for use in OBD2 computer control systems. An OBD2-compliant vehicle will employ one of the following protocols:

· ISO 9141-2

· SAE J1850 (VPW 10.4K)

· SAE J1850 (PWM 41.6K)

· ISO 14230-4 KW 2000

· ISO 15765 CAN (Control Area Network)

ISO 9141-2

Classification: A

Commonly Used On: European, Asian, and some Chrysler

Description:

The ISO 9141-2 protocol is essentially a serial interface, similar to the RS232 interface found in personal computers. The ISO 9141-2 data bus can be implemented as either a single-wire or two-wire interface (DLC pins 7 and 15) with a data transfer speed of up to 10.4 Kb/s. The “K” line (pin 7) is a bidirectional line. During initialization, this line carries address information or (in the case of fast initialization), the “wake up” pattern from the Code Reader or Scan Tool to the vehicle’s computer. After initialization, bidirectional data flow between the Code Reader or Scan Tool and the vehicle’s computer takes place over the “K” line. The “L” line (pin 15) is a unidirectional line (from the Code Reader or Scan Tool to the vehicle’s computer). It is used only during initialization to carry address information or (in the case of fast initialization), the “wake up” pattern from the Code Reader or Scan Tool to the vehicle’s computer simultaneously with the “K” line. After initialization, the “L” line is held in a “high” (logic “1”) state.

The ISO 9141-2 data signal is a square wave of uniform frequency, with a varying voltage level (either +12VDC or 0VDC), as illustrated.

ISO 14230-4 KW 2000

Classification: A

Commonly Used On: European, Asian, and some Chrysler

Description:

The ISO 14230-4 KW 2000 protocol is a variation of the ISO 9141-2 protocol, complying with the specific requirements of ISO 14230-2 and ISO 14230 Parts 2 and 3. The ISO ISO 14230-4 data bus can be implemented as either a single-wire or two-wire interface (DLC pins 7 and 15) with a data transfer speed of up to 10.4 Kb/s. The “K” line (pin 7) is a bidirectional line. During initialization, this line carries address information or (in the case of fast initialization), the “wake up” pattern from the Code Reader or Scan Tool to the vehicle’s computer. After initialization, bidirectional data flow between the Code Reader or Scan Tool and the vehicle’s computer takes place over the “K” line. The “L” line (pin 15) is a unidirectional line (from the Code Reader or Scan Tool to the vehicle’s computer). It is used only during initialization to carry address information or (in the case of fast initialization), the “wake up” pattern from the Code Reader or Scan Tool to the vehicle’s computer simultaneously with the “K” line. After initialization, the “L” line is held in a “high” (logic “1”) state.

The ISO 14230-4 KW 2000 data signal is a square wave of uniform frequency, with a varying voltage level (either +12VDC or 0VDC), as illustrated.

SAE J1850 (VPW 10.4K)

Classification: B

Commonly Used On: Chrysler and General Motors

Description:

The SAE J1850 (VPW 10.4K) data bus is implemented as a single-wire bidirectional interface (DLC pin 2), with a data transfer speed of 10.4 Kb/s. The data signal is a series of pulses of uniform amplitude (7VDC) and variable pulse width (VPW), as illustrated.
 

SAE J1850 (PWM 41.6K)

Classification: B

Commonly Used On: Ford

Description:

The SAE J1850 (PWM 41.6K) protocol is implemented as a two-wire bidirectional interface (DLC pins 2 and 10) that supports data transfer rates of up to 41.6 Kb/s. The “+” (pin 2) and “-“ (pin 10) bus lines carry differential signals; that is, the signal on the “-“ line is an exact inversion of the signal on the “+” line. This implementation minimizes the effects of Radio Frequency Interference (RFI) or Electromagnetic Interference (EMI) on the data signal.
The SAE J1850 (PWM 41.6K) data signal is a series of differential pulses of uniform amplitude (+5VDC, -5VDC) and modulated pulse width (PWM), as illustrated.
 

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ISO 15765 CAN (Control Area Network)

Classification: C

Commonly Used On: Beginning in 2008, all new vehicles will be required to use the CAN protocol

Description:

The ISO 15765 CAN protocol is implemented as a two-wire bidirectional interface (DLC pins 6 and 14) that supports data transfer rates of up to 1 Mb/s. The “High” (pin 6) and “Low“ (pin 14) bus lines carry differential signals; that is, the signal on the “Low“ line is an exact inversion of the signal on the “High” line. This implementation minimizes the effects of Radio Frequency Interference (RFI) or Electromagnetic Interference (EMI) on the data signal.
The ISO 15765 CAN data signal is a series of differential pulses of uniform amplitude (+5VDC, -5VDC) and modulated pulse width (PWM), as illustrated.
 

5, 10 Types Of OBD Diagnostic modes 

The OBD2 system is comprised of nine diagnostic operational modes, each of which supports retrieval of a specific set of diagnostic information. The nine diagnostic modes are:

MODE 1 – Powertrain Diagnostic Data

MODE 2 – Powertrain Freeze Frame Data

MODE 3 – Emission-related Diagnostic Trouble Codes (DTCs)

MODE 4 – Clear / Reset Emission-related Diagnostic Information

MODE 5 – Oxygen Sensor Test Results

MODE 6 –Non-continuous Test Results

MODE 7 – Continuous Monitors Test Results

MODE 8 – Control of On-board Tests and Devices

MODE 9 – Vehicle Information

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MODE 1 – Powertrain Diagnostic Data

In OBD2 systems, the vehicle’s on-board computer receives status information generated by the various vehicle sensors, switches and actuators located throughout the vehicle. This information includes values (volts, rpm, temperature, speed etc.) and system status information (open loop, closed loop, fuel system status, etc.).

MODE 1, Powertrain Diagnostic Data, retrieves "real time" signal values (also called ”Live Data”) generated by the sensors, actuators, switches and/or vehicle system status information used by the vehicle's computer when calculating and conducting system adjustments and corrections.

The real time vehicle operating information for each sensor, actuator, switch, etc. is called Parameter Identification (PID) Data. Each PID (sensor, actuator switch, status, etc.) has a set of operating characteristics and features (parameters) that serve to identify it. These “default” values are also retrieved through MODE 1.

(NOTE) The data retrieved is "real–time" Live Data. The values (volts, rpm, temperature, vehicle speed, system status etc) for the various PIDS may change as the vehicle's operating conditions change. Depending on the specific PID, data may show an actual value returned from a single device (snsor, actuator, switch, etc.), or may show a calculated value based on the inputs from multiple devices.

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Sampling Rate

The rate at which PIDs are sampled (the rate at which data is refreshed) varies, depending on the communication protocol used by the specific vehicle (see COMMUNICATION PROTOCOLS for more information). The powertrain PID sampling rates for each communication protocol are:

· SAE J1850 (VPW 10.4K), SAE J1850 (PWM 41.6K) – 150ms per PID

· ISO 9141-2, ISO 14230-4 KW 2000 – 90ms per PID

· ISO 15765 CAN – 50ms per PID

(NOTE) Actual refresh rate when viewing Live Data is cumulative, and depends on the number of PIDs selected for viewing at a given time. The greater the number of PIDs selected for display, the slower the refresh rate.

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MODE 1 PIDs

(NOTE) Not all PIDs are supported by all vehicles.

· PID 00 – PIDs supported by the ECU

· PID 01 – DTCs, MIL Status and Monitor Status

· PID 03 – Fuel System Status

· PID 04 – Calculated Load Value

· PID 05 – Engine Coolant Temperature

· PID 06 – STFT Bank 1

· PID 07 – LTFT Bank 1

· PID 08 – STFT Bank 2

· PID 09 – LTFT Bank 2

· PID 0A – Fuel Pressure

· PID 0B – Intake Manifold Absolute Pressure

· PID 0C – Engine RPM

· PID 0D – Vehicle Speed

· PID 0E – Ignition Timing #1 Cylinder

· PID 0F – Intake Air Temperature

· PID 10 – Air Flow Rate for MAF

· PID 11 – Absolute Throttle Position

· PID 12 – Secondary Air Status

· PID 13 – Oxygen Sensor Location

· PID 14 – Oxygen Sensor 1 Bank 1

· PID 15 – Oxygen Sensor 2 Bank 1

· PID 16 – Oxygen Sensor 1 Bank 2

· PID 17 – Oxygen Sensor 2 Bank 2

· PID 18 – Oxygen Sensor 1 Bank 3

· PID 19 – Oxygen Sensor 2 Bank 3

· PID 1A – Oxygen Sensor 1 Bank 4

· PID 1B – Oxygen Sensor 2 Bank 4

· PID 1C – OBD2 Support Requirement

· PID 1D – Alternate Oxygen Sensor Location

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PID 03 – Fuel System Status

Provides an indication of current fuel system status (closed loop, open loop, etc.)

Possible values for PID 04 are:

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PID 04 – Calculated Load Value

Provides a calculated value indicating the percent of engine capacity that is currently being used, derived as the ratio of current airflow divided by peak airflow (altitude corrected).

Possible values for PID 04 are:

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PID 05 – Engine Coolant Temperature

Provides a calculated value indicating current temperature of the engine coolant.

Possible values for PID 05 are:

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PID 06 – STFT Bank 1

Provides an indication, as a percentage, of short term fuel trim (STFT) adjustments made to the base fuel trim program, based on input(s) from the vehicle’s oxygen sensor(s). Positive numbers representincreased fuel delivery; negative numbers represent decreased fuel delivery.

Possible values for PID 06 are:

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PID 07 – LTFT Bank 1

Provides an indication, as a percentage, of long term fuel trim (LTFT) adjustments made to the base fuel trim program, based on the average of STFT fuel adjustments. Positive numbers represent increased fuel delivery; negative numbers represent decreased fuel delivery.

Possible values for PID 07 are:

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PID 08 – STFT Bank 2

Provides an indication, as a percentage, of short term fuel trim (STFT) adjustments made to the base fuel trim program, based on input(s) from the vehicle’s oxygen sensor(s). Positive numbers representincreased fuel delivery; negative numbers represent decreased fuel delivery.

Possible values for PID 08 are:

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PID 09 – LTFT Bank 2

Provides an indication, as a percentage, of long term fuel trim (LTFT) adjustments made to the base fuel trim program, based on the average of STFT fuel adjustments. Positive numbers represent increased fuel delivery; negative numbers represent decreased fuel delivery.

Possible values for PID 09 are:

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PID 0A – Fuel Rail Pressure

Provides a calculated value indicating current fuel rail pressure.

Possible values for PID 0A are:

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PID 0B – Intake Manifold Absolute Pressure

Provides a calculated value indicating current intake manifold absolute pressure (as either pressure or vacuum).

Possible values for PID 0B are:

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PID 0C – Engine RPM

Provides a calculated value (derived from either an analog or digital input signal) indicating current engine operating speed in revolutions per-minute.

Possible values for PID 0C are:

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PID 0D – Vehicle Speed

Provides a calculated value indicating the speed at which the vehicle is currently traveling.

Possible values for PID 0D are:(8.31)

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PID 0E – Ignition Timing #1 Cylinder

Provides an indication of the amount of advance the vehicle’s on-board computer is applying to the #1 cylinder. This value does not include mechanical advance.

Possible values for PID 0E are:

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PID 0F – Intake Air Temperature

Provides a calculated value indicating current intake air temperature.

Possible values for PID 0F are:

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PID 10 – Air Flow Rate for MAF

Provides a calculated value representing airflow rate through the Mass Airflow Air Flow Sensor; typically low at idle to high at wide open throttle.

Possible values for PID 10 are:

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PID 11 – Absolute Throttle Position

Provides a representation of current throttle position (throttle opening) as a percentage. The value may be displayed as either a “low-to-high” percentage (1% at closed throttle, 95% at wide open throttle) or as a “high-to-low” percentage (high at idle, low at wide open throttle)

Possible values for PID 11 are:

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PID 13 – Oxygen Sensor Location

Provides an indication of the location of the vehicle’s oxygen sensor(s) (see Oxygen Sensor Designations for more information).

Possible values for PID 13 are:

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PID 14 – Oxygen Sensor 1 Bank 1

Provides an indication of the operating voltage or current for Oxygen Sensor 1 Bank 1.

Possible values for PID 14 are:

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PID 15 – Oxygen Sensor 2 Bank 1

Provides an indication of the operating voltage or current for Oxygen Sensor 2 Bank 1.

Possible values for PID 15 are:

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PID 16 – Oxygen Sensor 1 Bank 2

Provides an indication of the operating voltage or current for Oxygen Sensor 1 Bank 1.

Possible values for PID 16 are:

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PID 17 – Oxygen Sensor 2 Bank 2

Provides an indication of the operating voltage or current for Oxygen Sensor 1 Bank 1.

Possible values for PID 17 are:

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PID 18 – Oxygen Sensor 1 Bank 3

Provides an indication of the operating voltage or current for Oxygen Sensor 1 Bank 1.

Possible values for PID 18 are:

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PID 19 – Oxygen Sensor 2 Bank 3

Provides an indication of the operating voltage or current for Oxygen Sensor 1 Bank 1.

Possible values for PID 19 are:

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PID 1A – Oxygen Sensor 1 Bank 4

Provides an indication of the operating voltage or current for Oxygen Sensor 1 Bank 1.

Possible values for PID 1A are:

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PID 1B – Oxygen Sensor 2 Bank 4

Provides an indication of the operating voltage or current for Oxygen Sensor 1 Bank 1.

Possible values for PID 1B are:

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PID 1C – OBD2 Support Requirement

Provides an indication of the OBD systems/types supported by the vehicles on-board computer.

Possible values for PID 1C are:

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MODE 2 – Powertrain Freeze Frame Data

In OBD2 systems, when an emissions-related engine malfunction occurs that causes a DTC to set, a record or snapshot of actual engine conditions (not default or substituted values used by the vehicle’s on-board computer) at the time that the malfunction occurred is also saved in the vehicle’s computer memory. The record saved is called “Freeze Frame data.” Saved engine conditions include, but are not limited to: engine speed, open or closed loop operation, fuel system commands, coolant temperature, calculated load value, fuel pressure, vehicle speed, air flow rate, and intake manifold pressure.

MODE 2, Powertrain Freeze Frame Data, retrieves Freeze Frame Data from the vehicle’s on-board computer.

(NOTE) If more than one malfunction is present that causes more than one DTC to be set, only the code with the highest priority will contain Freeze Frame data. The priority code is the one that has commanded the MIL on.

(NOTE) A Misfire or Fuel System Fault will overwrite all other Freeze Frame Data.

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MODE 3 – Emission-related Diagnostic Trouble Codes (DTCs)

Diagnostic Trouble Codes (DTCs) are alpha-numeric codes that are used to identify a problem that is present in any of the systems that are monitored by the vehicle’s on-board computer. When the vehicle's on-board computer detects a failure in an emissions-related component or system, the computer's internal diagnostic program assigns a Diagnostic Trouble Code (DTC) that points to the system (and subsystem) where the fault was found and saves the code in the computer's memory (see DIAGNOSTIC TROUBLE CODES for more information).

There are two types of DTCs used for emissions-related faults in OBD2 systems: Type “A” (“hard” codes) and Type “B” (“pending” codes). Type “A” codes are “One Trip” codes. Type “B” codes are usually “Two Trip” codes. MODE 3, Emission-related Diagnostic Trouble Codes (DTCs), retrieves “hard” codes from the vehicle’s on-board computer (“pending” codes are retrieved by MODE 7).

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MODE 4 – Clear / Reset Emissions-related Diagnostic Information

MODE 4, Clear / Reset Emissions-related Diagnostic Information, clears (erases) all diagnostic information (DTCs, Freeze Frame Data, O2 sensor test results, Monitor status, etc.) from the computer’s memory.

(NOTE) This function is generally performed only after codes have been retrieved, and necessary corrective actions have been performed. DO NOT erase diagnostic information from the vehicle's computer until repairs have been accomplished. If the data is erased, valuable information that might help troubleshoot the problem will be lost.

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MODE 5 – Oxygen Sensor Test Results

OBD2 regulations require that applicable vehicles monitor and test operation of the oxygen (O2) sensors to identify problems that can affect fuel efficiency and vehicle emissions. These tests are performed automatically when engine operating conditions are within predefined limits. Results of these tests are stored in the on-board computer's memory. Once stored, test results are retained in the computer’s memory until they are overwritten by more current test results.

MODE 5, Oxygen Sensor Test Results, retrieves test results for the most recently completed tests of the vehicle’s oxygen sensor(s).

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Oxygen Sensor Designations

Vehicles are equipped with multiple O2 sensors. O2 sensors are installed both upstream of (before) and downstream of (after) the exhaust system Catalytic Converters. The name of an O2 sensor identifies its location in the exhaust system. The name of each O2 sensor is made up of three parts:

O2S XX YY -or- O2S X Y

· O2S -this is the basic designation for all O2 sensors.

· X or XX - These characters identify the location of the O2 sensor in relation to a cylinder bank. An O2 sensor for cylinder bank 1 is identified by the designation “1” or "B1"; a sensor for cylinder bank 2 is identified as “2” or "B2."

(NOTE) “Bank One” indicates the side of the engine where cylinder number one is located (V-type engines). Bank Two is opposite of Bank One.

· Y or YY - These characters identity the location of the O2 sensor in relation to the exhaust system catalyst. An O2 sensor located upstream of the catalyst is identified by the designation”1” or "S1", a sensor located downstream of the Catalytic Converter is identified as “2” or "S2."

For example, O2S12 or O2SB1S2 is the designation for the downstream O2 sensor for cylinder bank 1.

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Oxygen Sensor Test Results

Oxygen sensor test results include the following information:

· $01 – Rich-to-lean threshold voltage

· $02 – Lean-to-rich threshold voltage

· $03 – Low sensor voltage switch time

· $04 – High sensor voltage switch time

· $05 – Rich-to-lean sensor switch time

· $06 – Lean-to-rich sensor switch time

· $07 – Minimum voltage for test cycle

· $08 – Maximum voltage for test cycle

· $09 – Time between sensor transitions

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MODE 6 – Non-continuous Test Results

MODE 6, Non-continuous Test Results, retrieves test results for emission-related powertrain components and systems that are not continuously monitored. The tests available are determined by the vehicle manufacturer.

This diagnostic mode does not command the vehicle’s computer to perform the tests, but retrieves results from the most recently performed tests from the computer’s memory.

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MODE 7 – Continuous Monitors Test Results

Diagnostic Trouble Codes (DTCs) are alpha-numeric codes that are used to identify a problem that is present in any of the systems that are monitored by the vehicle’s on-board computer. When the vehicle's on-board computer detects a failure in an emissions-related component or system, the computer's internal diagnostic program assigns a Diagnostic Trouble Code (DTC) that points to the system (and subsystem) where the fault was found and saves the code in the computer's memory (see DIAGNOSTIC TROUBLE CODES for more information).

There are two types of DTCs used for emissions-related faults in OBD2 systems: Type “A” (“hard” codes) and Type “B” (“pending” codes). Type “A” codes are “One Trip” codes. Type “B” codes are usually “Two Trip” codes. MODE 7, Emission-related Diagnostic Trouble Codes (DTCs), retrieves “pending” codes from the vehicle’s on-board computer (“hard” codes are retrieved by MODE 3).

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MODE 8 – Control of On-board Tests and Devices

MODE 8 , Control of On-board Tests and Devices, is a bidirectional test mode that allows external test equipment (such as a Code Reader or Scan Tool) of an on-board system, test, or component. This diagnostic mode lets the external device command the vehicle’s on-board computer to initiate or perform one or more specific tests, and retrieve test results.

The specific components/systems for which test results are available vary between vehicle manufacturers, makes and models. Currently, implementation of MODE 8 is limited. However, CARB is reviewing this functionality for possible future expansion.

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MODE 9 – Vehicle Information

MODE 9, Vehicle Information, retrieves vehicle-specific reference information including the Vehicle Identification Number (VIN), Calibration IDs, Calibration Verification Number and In–use performance tracking counts.

6, Definition of Terms 

The following terms are related to on-board diagnostic systems. Read and reference this list as needed to aid in the understanding of OBD2 systems.

CARB – California Air Resources Board

“Check Engine” Light- See “Malfunction Indicator Lamp (MIL)”

Communication Protocol – The method or means by which data is transferred between the vehicle’s on-board computer and an external data retrieval device, such as a Code Reader or Scan Tool.

Computer Control System – An electronic control system, consisting of an on-board computer and related sensors, actuators and switches, used to ensure peak performance and fuel efficiency while reducing pollutants in the vehicle’s emissions. OBD1 and OBD2 systems are computer control systems.

Continuous Monitor – See “:Monitors”

Data Link Connector (DLC) – An electrical connector that provides the means of accessing and retrieving data from the vehicle’s on-board computer. OBD1 systems employ a variety of manufacturer-specific connectors. OBD2 Systems use a standardized 16-pin DLC, as defined by SAE J1962/ISO 15031-3.

Diagnostic Trouble Code (DTC) - Numeric (OBD1 systems) or alpha-numeric (OBD2 systems) codes that are used to identify a problem that is present in any of the systems that are monitored by the vehicle’s on-board computer. In OBD1 systems, DTCs are manufacturer- and/or model-specific. In OBD2 systems, DTCs can be “generic” or “manufacturer-specific.”

Generic DTC – A DTC that applies to all OBD2-compliant vehicles.

Manufacturer-Specific DTC – A DTC that applies only to OBD2-compliant vehicle’s made by a specificmanufacturer.

Driving Condition – A specific environmental or operational condition under which a vehicle is driven (operated); such as starting the vehicle when cold, driving at steady speed (cruising), accelerating, etc.

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Enabling Criteria - Each Monitor is designed to test and monitor the operation of a specific part of the vehicle's emissions system (EGR system, oxygen sensor, catalytic converter, etc.). A specific set of "conditions" or "driving procedures" must be met before the computer can command a Monitor to run tests on its related system. These "conditions" are known as "Enabling Criteria." The requirements and procedures vary for each Monitor. Some Monitors only require the ignition key to be turned "On" for them to run and complete their diagnostic testing. Others may require a set of complex procedures, such as, starting the vehicle when cold, bringing it to operating temperature, and driving the vehicle under specific conditions before the Monitor can run and complete its diagnostic testing.

EPA – Environmental Protection Agency

Freeze Frame Data – A digital representation or “snapshot” of engine and/or emissions system conditions present when a given Diagnostic Trouble Code (DTC) was stored. The vehicle’s computer stores Freeze Frame Data for the priority DTC only.

Fuel Trim – A vehicle requires a mixture of air and fuel to achieve combustion. The optimal mixture of air and fuel is known as the stoichiometric ratio, and is generally defined as 14.7:1 times the mass of air to fuel. To ensure optimum engine performance with the least amount of pollution, the vehicle’s computer constantly monitors the air/fuel mixture, and adjusts it according to current driving requirements. The vehicle’s computer stores predetermined “reference” values for air/fuel ratio for all possible driving conditions (base fuel trim). The computer receives inputs from sensors (primarily the Engine Coolant Temperature Sensor and Oxygen Sensor) and compares the “actual” values from these sensors with the programmed reference values. If the sensor input values do not match the “reference” values for that particular driving condition, the computer command the proper components (actuators) to make corrections (fuel trim adjustments). Fuel trim adjustments can be “short term” or “long term.”

Short Term Fuel Trim (STFT) – The vehicle’s computer makes adjustments to the base fuel trim program by adding or subtracting fuel from the base program (to achieve the optimum air/fuel ratio) based on inputs from the vehicle’s Oxygen Sensor(s).

Long Term Fuel Trim (LTFT) - The vehicle’s computer makes adjustments to the base fuel trim program by adding or subtracting fuel from the base program (to achieve the optimum air/fuel ratio) based on theaverage of STFT fuel corrections. LTFT adjustments often mask underlying problems such as MAF sensor problems, leaking fuel injectors, leaking intake manifold gaskets, etc.

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Generic DTC – See “Diagnostic Trouble Code (DTC)”

I/M Readiness – I/M is an Inspection and Maintenance program legislated by the Government to me federal clean-air standards. The program requires that a vehicle be taken to an “Emissions Test Station” for an “Emissions Test” or “Smog Check,” where the emissions-related components and systems are inspected and tested for proper operation.

I/M Readiness Status – I/M Readiness status is determined by checking the state of a vehicle’s Monitors for “has run” or “has not run” status. If all supported Monitors for a vehicle show a “has run” status it indicates that all monitored emissions-related components and systems are operating properly; the vehicle is ready for an Emissions Test, and there is a strong possibility that it can be certified. Any Monitor that shows a “has not run” status, it may indicate a problem in the monitored component or system. Depending on local regulations, the vehicle may or may not be ready for an Emissions Test.

(NOTE) Some areas require that all Monitors indicate a “has run” status before an Emissions Test can be performed. Other areas only require that some, but not all Monitors have run their self-diagnostic testing before an Emissions Test can be performed.

Kb/s– Kilobytes-per-second. Used to specify the speed at which data transfers take place.

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Live Data – “Real time” vehicle operational values (volts, rpm, temperature, speed, etc.) generated by sensors, actuators and switches throughout the vehicle. This information can be accessed via the vehicle’s computer and viewed using a Scan Tool. The “real time” vehicle operating information (values/status) that the vehicle’s computer supplies to the Scan Tool for each sensor, actuator, switch, etc., is called Parameter Identification (PID) Data.

Long Term Fuel Trim (LTFT) – See “Fuel Trim”

Malfunction Indicator Lamp (MIL) – Dashboard-mounted indicator lamp that lights when the vehicle’s on-board computer detects a failure in an emissions-related component or system that causes a Diagnostic Trouble Code (DTC) to be saved to the computer’s memory. The MIL is also referred to as a “Check Engine” light.

Manufacturer-Specific DTC – See “Diagnostic Trouble Code (DTC)”

Mb/s– Megabytes-per-second. Used to specify the speed at which data transfers take place.

Monitor - Monitors are "diagnostic routines" programmed into the PCM. The PCM utilizes these programs to run diagnostic tests, and to monitor operation of the vehicle's emissions-related components or systems to ensure they are operating correctly and within the vehicle's manufacturer specifications. Currently, up to eleven Monitors are used in OBD 2 systems. Additional Monitors will be added as the OBD 2 system is further developed. Monitor operation is either "Continuous" or "Non-Continuous," depending on the specific monitor.

Continuous Monitors – Continuous Monitors are designed to continuously monitor their associated components and/or systems for proper operation. Continuous Monitors run constantly when the engine is running.

Non-Continuous Monitors - Non-continuous Monitors perform and complete their testing once per trip.

(NOTE) Not all vehicles support all eleven Monitors.

Monitor Has/Has Not Run - The terms "Monitor has run" or "Monitor has not run" are used throughout this manual. "Monitor has run," means the PCM has commanded a particular Monitor to perform the required diagnostic testing on a system to ensure the system is operating correctly (within factory specifications). The term "Monitor has not run" means the PCM has not yet commanded a particular Monitor to perform diagnostic testing on its associated part of the emissions system.

ms - milliseconds

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Non-Continuous Monitor – See “Monitors”

OBD1 – On-Board Diagnostics Version 1 (also referred to as “OBD I”)

OBD2 – On-Board Diagnostics Version 2 (also referred to as “OBD II”)

OBD2 Drive Cycle - An OBD 2 Drive Cycle is an extended set of driving procedures that takes into consideration the various types of driving conditions encountered in real life. These conditions may include starting the vehicle when it is cold, driving the vehicle at a steady speed (cruising), accelerating, etc. An OBD 2 Drive Cycle begins when the ignition key is turned "On" (when cold) and ends when the vehicle has been driven in such a way as to have all the "Enabling Criteria" met for all its applicable Monitors. Only those trips that provide the Enabling Criteria for all Monitors applicable to the vehicle to run and complete their individual diagnostic tests qualify as an OBD 2 Drive Cycle. OBD 2 Drive Cycle requirements vary from one model of vehicle to another. Vehicle manufacturers set these procedures.

On-Board Computer – See “Powertrain Control Module (PCM)”

Parameter Identification (PID) Data – See “Live Data”

Pending Code – A DTC recorded on the “first trip” for a “two trip” code. If the fault that caused the code to be set is not detected on the second trip, the code is automatically erased.

Powertrain Control Module (PCM) - The PCM is the OBD 2 accepted term for the vehicle's "on-board computer." The PCM is the central processing unit in the vehicle’s computer control system. In addition to controlling the engine management and emissions systems, the PCM also participates in controlling the powertrain (transmission) operation. Most PCMs also have the ability to communicate with other computers on the vehicle (ABS, ride control, body etc.).

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Short Term Fuel Trim (STFT) – See “Fuel Trim”

Trip - A Trip for a particular Monitor requires that the vehicle is driven in such a way that all the "Enabling Criteria" for the Monitor to run and complete its diagnostic testing are met. The "Trip Drive Cycle" for a particular Monitor begins when the ignition key is turned "On." It is successfully completed when all the "Enabling Criteria" for the Monitor to run and complete its diagnostic testing are met by the time the ignition key is turned "Off." Since each of the eleven monitors is designed to run diagnostics and testing on a different part of the engine or emissions system, the "Trip Drive Cycle" needed for each individual Monitor to run and complete varies.

(NOTE) Do not confuse a "Trip" Drive Cycle with an OBD 2 Drive Cycle. A Trip Drive Cycle provides the "Enabling Criteria" for one specific Monitor to run and complete its diagnostic testing. An OBD 2 Drive Cycle must meet the "Enabling Criteria" for all Monitors on a particular vehicle to run and complete their diagnostic testing.

Warm-up Cycle - Vehicle operation after an engine off period where engine temperature rises at least 40°F (22°C) from its temperature before starting, and reaches at least 160°F (70°C). The PCM uses warm-up cycles as a counter to automatically erase a specific code and related data from its memory. When no faults related to the original problem are detected within a specified number of warm-up cycles, the code is erased automatically.