Diagnostic fault codes adapted to newlegal requirements
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Diagnostic fault 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).
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.
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:
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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:
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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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