Diagnostic trouble codes adapted to new legal requirements
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Diagnostic trouble codes adapted to new legal requirements
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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).
For 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 diagnosis trouble codes 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 (diagnostic trouble codes and documents) and SAE J-1979 (commands).
Intermittent faults
With the advent of the new diagnostic trouble codes, the previous unique code for an intermittent fault has been discontinued. This does not mean that it will no longer be possible to detect an intermittent fault, but the new method of obtaining an intermittent fault readout is different to the previous method. Basically, the following will apply:
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CHECK ENGINE lamp on and diagnostic trouble code = permanent fault
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CHECK ENGINE lamp out and diagnostic trouble code = intermittent fault
The new diagnostic trouble codes consist of five characters, the first is a letter and the other four are figures (e.g. P0111). The letter denotes system affiliation, as follows:
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B = Body
In addition to these is the letter U (Undefined), which is in reserve.
The figure immediately after the letter indicates whether the code is associated with a legal requirement according to SAE (0) or 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:
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P04xx Exhaust emission control system
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P05xx Speed/idling control
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P06xx Control module and control module output signals
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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.
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