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1991 Audi 90 diagnostics

In message <3402F0FC@smtpgw.ipex.com.au> Mark Zvolanek writes:

> My Audi has a fuse slot on fuel pump relay, could that imply something?

Yup.  It implies you haven't got them.
More specifically, it implies that you have a K-Jetronic controller and not a 
Motronic controller.  The codes in this system are volatile and will be erased 
if the ignition is switched off.  The procedure is:
Audi quattro self-diagnosis (MB engine)

The term "self-diagnosis" refers to electronically
controlled systems that are equipped with an error code
storage system.

Problems encountered while driving are logged in the
control unit's storage.  The contents are retained only
while the ignition is switched on, i.e., if the ignition
is turned off, the error logs are lost.

If an error which could result in engine damage occurs,
this is also signalled via the warning light on the

This warning lamp must illuminate whenever the ignition
is turned on.

If this light does not illuminate when the ignition is
turned on, bridge the contacts on the top of the fuel
pump relay with a spare fuse.  The warning light should
come on - if it does not, trace the wiring according to
the wiring diagram.

Reading the error codes.

The error codes can be read from the engine electronics
warning light.  Each code consists of four groups of
pulses.  There is a pause of around 2.5 seconds between
each group.  The pulses in each group are counted (there
are never more than four) to derive a four-digit code.
These are listed below.

The exact sequence for each code is a start sequence of
2.5 seconds with the lamp on, and 2.5 with it off.  The
codes then follow as half-second pulses separated by half-
second pulses, with a larger gap of 2.5 seconds between
each group.  The sequence is repeated until the system is
stepped to the next error log by bridging the contacts on
the fuel pump relay.  The lamp blinks at 2.5 second
intervals to indicate that the last error code has been

The sequence is terminated if the ignition is switched
off or the engine exceeds 2,500 rpm.


  Fuse 24 OK
  Control unit power OK
  Engine warning lamp OK
  Fuel pump relay OK.

If the engine runs, start it and test drive the vehicle.
The engine should be revved above 3,000 rpm, positive
boost pressure should be used and the accelerator should
be fully depressed at least once.  At the end of the test
drive, do not switch off the engine.

If the engine will not run, turn it on the starter for at
least five seconds.  Leave the ignition switched on, and
proceed as if a test drive has been performed.

With a spare blade relay, bridge the contacts provided
for the purpose on top of the fuel pump relay for at
least 4 seconds.  The engine warning lamp will then pulse
out the first error code.  If there is no error logged,
the system will pulse out "4444", i.e., the warning light
will illuminate once for 2.5 seconds, then go off for 2.5
seconds, then pulse four times at half second intervals.
After a pause of 2.5 seconds, it will again pulse four
times, reading out the second "4".

Note down the error code, if any, and repeat the 4 second
bridging of the fuel pump relay contacts.  The next code
will be displayed.  If the lamp merely flashes at 2.5
second intervals, the last error code has been read out.
If multiple errors have been logged, they should be dealt
with in the order the system reads them out.

Code Source            Possible cause          Check

1111 Control Unit      Defective processor     Replace unit

2111 RPM sender        Open or short circuit,
                       defective sensor        Sensor & cables

2112 Timing sender     As RPM, or flywheel
                       peg mislocated          Sensor & 
                                               flywheel peg

2113 Hall sender       As RPM, or distributor
                       mislocated              Sensor &

2121 Idle switch       As RPM, or switch stuck 
                       in position             Switch and cabling

2123 Full load switch  As idle switch          As above

2141 Knock regulator   Fuel octane too low     Compression,
                                               injection, boost

2142 Knock sensor      Open or short circuit,
                       defective sensor        Sensor and cabling

2221 Vacuum hose       Vacuum hose to
                       controller defective    Check hose

2222 Pressure sensor   Control unit's pressure
                       sensor defective        Replace unit

2312 Coolant sensor    Open or short circuit,
                       defective sensor        Sensor and cables

2322 Inlet air temp.   As above                As above

2214 Over-revved       Engine has exceeded
                       rev limit               Driver
2224 Excess boost      Wastegate or pressure
                       tubing                  Wastegate and

 Phil Payne
 Committee Member, UK Audi [ur-]quattro Owners Club