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Diagnostic fault codes adapted to newlegal requirements

Diagnostic fault codes adapted to new legal requirements


Since 1988, motor manufacturers have been required by the authorities in California (later followed by other countries around the world) to incorporate "smart" control systems in the car for the purpose of detecting and localizing emission- related faults with the aid of OBD (On-Board Diagnostics).

From model year 1993 and later cars, the Californian requirements were further sharpened through the introduction of OBD II. In part, the new requirements entailed a standardization of the structure of fault diagnosis and command codes. This was done in order to achieve a degree of uniformity between different motor manufacturers and so make things easier for mechanics and other garage personnel who work on several different systems and makes of car. Recommendations for this standardization are to be found in documents SAE J-2012 (fault codes and documents) and SAE J-1979 (commands).

In view of the above, the diagnostic trouble codes for the M1994 MOTRONIC system are different to those we had become accustomed to earlier when using an ISAT for obtaining readouts of diagnostic trouble codes.

Intermittent faults

For the MOTRONIC 2.8.1 there are no separate diagnostic trouble codes for intermittent faults. The same diagnostic trouble code is used, but the suffix P or I indicates whether the fault is Permanent or Intermittent.

The new diagnostic trouble codes consist of five characters. The first character is a letter and the other four are figures (e.g. P0111). The letter denotes system affiliation, as follows:



P = Power train

C = Chassis

B = Body

Also used in addition to the above is the letter U (Undefined), which is in reserve.

The figure after the letter indicates whether the code is associated with a legal requirement according to SAE (0) or whether it is a unique manufacturer's code (1 or 2).

The second figure after the letter shows the subsystem in the relevant main group to which the diagnostic trouble code refers.

For Power train diagnostic trouble codes, the second figure signifies the following:

P01xx Fuel/air supply

P02xx Fuel/air supply

P03xx Ignition system

P04xx Exhaust emission control system

P05xx Speed/idling control

P06xx Control module and control module output signals

P07xx Transmission

P08xx Transmission

P09xx Reserved for SAE

P00xx Reserved for SAE

Finally, the last two figures in the diagnostic trouble code comprise a serial number which gives each diagnostic trouble code a unique number in the respective group.