OBD Knowledge

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:

PID Description	Unit	Value
Fuel System 1 Status	-	OL
Fuel System 1 Status	-	CL
Fuel System 1 Status	-	OL-Drive
Fuel System 1 Status	-	OL-Fault
Fuel System 1 Status	-	CL-Fault
Fuel System 2 Status	-	OL
Fuel System 2 Status	-	CL
Fuel System 2 Status	-	OL-Drive
Fuel System 2 Status	-	OL-Fault
Fuel System 2 Status	-	CL-Fault

 

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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:

PID Description	Unit	Value
Calculated LOAD Value	%	XXX.X

 

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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:

PID Description	Unit	Value
Engine Coolant Temp	*C / *F	XXX / XXX

 

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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 represent increased fuel delivery; negative numbers represent decreased fuel delivery.

Possible values for PID 06 are:

PID Description	Unit	Value
Short Term Fuel Trim-Bank 1	%	XXX.X
Bank 1 - Sensor 1	%	XXX.X
Bank 1 - Sensor 2	%	XXX.X
Bank 1 - Sensor 3	%	XXX.X
Bank 1 - Sensor 4	%	XXX.X

 

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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:

PID Description	Unit	Value
Long Term Fuel Trim-Bank 1	%	XXX.X

 

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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 represent increased fuel delivery; negative numbers represent decreased fuel delivery.

Possible values for PID 08 are:

PID Description	Unit	Value
Short Term Fuel Trim-Bank 2	%	XXX.X
Bank 2 - Sensor 1	%	XXX.X
Bank 2 - Sensor 2	%	XXX.X
Bank 2 - Sensor 3	%	XXX.X
Bank 2 - Sensor 4	%	XXX.X

 

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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:

PID Description	Unit	Value
Long Term Fuel Trim-Bank 1	%	XXX.X

 

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PID 0A – Fuel Rail Pressure

Provides a calculated value indicating current fuel rail pressure.

Possible values for PID 0A are:

PID Description	Unit	Value
Fuel Rail Pressure	kPa /PSI	XXX / XX.X
Fuel Rail Pressure	kPa /PSI	XXXXX /XXXX.X

 

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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:

PID Description	Unit	Value
Intake Manifold Absolute Pressure	kPa /PSI	XXX / XX.X

 

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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:

PID Description	Unit	Value
Engine RPM	rpm	XXXXX

 

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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:

PID Description	Unit	Value
Vehicle Speed Sensor	km/h / mph	XXX / XXX

 

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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:

PID Description	Unit	Value
Ignition Timing Advance #1 Cylinder	deg	XX

 

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PID 0F – Intake Air Temperature

Provides a calculated value indicating current intake air temperature.

Possible values for PID 0F are:

PID Description	Unit	Value
Intake Air Temperature	*C / *F	XXX / XXX

 

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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:

PID Description	Unit	Value
Air Flow Rate from Mass Air Flow Sensor	g/s; lb/min	XXX.XX / XXXX.X

 

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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:

PID Description	Unit	Value
Absolute Throttle Position	%	XXX.X
Absolute Throttle Position B	%	XXX.X
Absolute Throttle Position C	%	XXX.X

 

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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:

PID Description	Unit	Value
Oxygen Sensor, Bank 1, Sensor 1	-	O2S11
Oxygen Sensor, Bank 1, Sensor 2	-	O2S12
Oxygen Sensor, Bank 1, Sensor 3	-	O2S13
Oxygen Sensor, Bank 1, Sensor 4	-	O2S14
Oxygen Sensor, Bank 2, Sensor 1	-	O2S21
Oxygen Sensor, Bank 2, Sensor 1	-	O2S22
Oxygen Sensor, Bank 2, Sensor 3	-	O2S23
Oxygen Sensor, Bank 2, Sensor 4	-	O2S24
Oxygen Sensor, Bank 1, Sensor 1	-	O2S11
Oxygen Sensor, Bank 1, Sensor 2	-	O2S12
Oxygen Sensor, Bank 2, Sensor 1	-	O2S21
Oxygen Sensor, Bank 2, Sensor 2	-	O2S22
Oxygen Sensor, Bank 3, Sensor 1	-	O2S31
Oxygen Sensor, Bank 3, Sensor 2	-	O2S32
Oxygen Sensor, Bank 4, Sensor 1	-	O2S41
Oxygen Sensor, Bank 4, Sensor 2	-	O2S42

 

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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:

PID Description	Unit	Value
Sensor 1 - Bank 1	V	X.XXX
Sensor 1 - Bank 1 O2S Current	mA	X.XXX
Sensor 1 - Bank 1 O2S Voltage	V	X.XXX

 

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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:

PID Description	Unit	Value
Sensor 2 - Bank 1	V	X.XXX
Sensor 2 - Bank 1 O2S Current	mA	X.XXX
Sensor 2 - Bank 1 O2S Voltage	V	X.XXX

 

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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:

PID Description	Unit	Value
Sensor 1 - Bank 2	V	X.XXX
Sensor 1 - Bank 2 O2S Current	mA	X.XXX
Sensor 1 - Bank 2 O2S Voltage	V	X.XXX

 

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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:

PID Description	Unit	Value
Sensor 2 - Bank 2	V	X.XXX
Sensor 2 - Bank 2 O2S Current	mA	X.XXX
Sensor 2 - Bank 2 O2S Voltage	V	X.XXX

 

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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:

PID Description	Unit	Value
Sensor 1 - Bank 3	V	X.XXX
Sensor 1 - Bank 3 O2S Current	mA	X.XXX
Sensor 1 - Bank 3 O2S Voltage	V	X.XXX

 

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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:

PID Description	Unit	Value
Sensor 2 - Bank 3	V	X.XXX
Sensor 2 - Bank 3 O2S Current	mA	X.XXX
Sensor 2 - Bank 3 O2S Voltage	V	X.XXX

 

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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:

PID Description	Unit	Value
Sensor 1 - Bank 4	V	X.XXX
Sensor 1 - Bank 4 O2S Current	mA	X.XXX
Sensor 1 - Bank 4 O2S Voltage	V	X.XXX

 

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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:

PID Description	Unit	Value
Sensor 2 - Bank 4	V	X.XXX
Sensor 2 - Bank 4 O2S Current	mA	X.XXX
Sensor 2 - Bank 4 O2S Voltage	V	X.XXX

 

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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:

PID Description	Unit	Value
OBD Requirements	-	OBD2
OBD Requirements	-	OBD
OBD Requirements	-	OBD and OBD2
OBD Requirements	-	OBD1
OBD Requirements	-	No OBD
OBD Requirements	-	EOBD
OBD Requirements	-	EOBD and OBD2
OBD Requirements	-	EOBD and OBD
OBD Requirements	-	EOBD, OBD and OBD2
OBD Requirements	-	JOBD
OBD Requirements	-	JOBD and OBD2
OBD Requirements	-	JOBD and EOBD
OBD Requirements	-	JOBD, EOBD and OBD2

 

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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.