obd2 diagnosis

What is a Diagnostic Trouble Code (DTC)?

Diagnostic trouble codes (or fault codes) are codes that are stored by the on-board computer diagnostic system. These are stored in response to a problem found in the car by the system. These codes are stored when a sensor in the car reports a reading that is outside the normal/accepted range (Eg: fuel mixture too rich).

These DTC's identify a particular problem area and are intended to provide the technician with a guide as to where a fault might be occurring within the vehicle.

Codes should be used in conjunction with the vehicle's service manual to discover which systems, circuits or components should be tested to fully diagnose the fault with a car code reader or professional OBD2 software.

Caution when Relying Only on Diagnostic Trouble Codes...

Parts or components should not be replaced with reference to only a DTC. The vehicle service manual should be consulted for more information on possible causes of the fault, along with required testing.

For example, if a DTC reports a sensor fault, replacement of the sensor is unlikely to resolve the underlying problem. The fault is most likely to be caused by the systems that the sensor is monitoring, but might even be caused by the wiring to the sensor itself.

DTCs may also be triggered by faults earlier down the line. For example, a dirty MAF sensor might be causing the car to overcompensate in its fuel-trim adjustments. As a result, oxygen sensors are likely to report fuel mixture problems.

So to avoid unpredictable hazards when fixing a vehicle based on it's DTC codes -- make sure you get a reliable OBD2 reader that'll thoroughly scan the vehicle for faults beyond traditional DTC codes.

Explanation of Codes

This page lists 5,000+ generic and manufacturer OBD2 Diagnostic Trouble Codes.

You can also access the database by downloading the printable offline version (ideal for auto mechanics).

If your vehicles code is not found on this page, then downloaded our free Windows OBD Code Lookup Software — which also includes car manufacturer codes.

TIP: This helpful resource site will reveal problem, cause, solution for every fault code.

NOTE: If your existing OBD software or scanner is not returning helpful data, you may want to consider getting advanced OBD2 scanner like TOAD which will dig a lot deeper into your car's performance, health, chip data.

Difference Between Generic & Manufacturer Specific...

In general, codes that begin with P0 are Generic codes, whereas codes that begin with P1 are manufacturer-specific.

Additional code groups are however available to allow for expansion of these code lists.

Code Type


Generic(normally P0xxx)

The definition for the code is defined in the EOBD / OBD-II standard and will be the same for all manufacturers.

Manufacturer-specific(normally P1xxx)

Where manufacturers feel that a code is not available within the generic list, they can add their own codes. The definitions for these are set by the manufacturer.




P0xxx - Generic

P1xxx - Manufacturer-specific

P0xxx - Generic

P30xx-P33xx - Manufacturer -specific

P34xx-P39xx - Generic



C0xxx - Generic

C1xxx - Manufacturer-specific

C2xxx - Manufacturer-specific

C3xxx - Generic



B0xxx - Generic

B1xxx - Manufacturer-specific

B2xxx - Manufacturer-specific

B3xxx - Generic

Network Communication codes

U0xxx - Generic

U1xxx - Manufacturer-specific

U2xxx - Manufacturer-specific

U3xxx - Generic

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P Codes (Powertrain), P0000 to 3499

B Codes (Body), B1200 to B2606

C Codes (Chasis), C1091 to C1963

U Codes (User Network), U1000 to U2500

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