Mono-Jetronic, Mono-Motronic up to 9/93
The electronics of the control unit makes it possible to recognize faults in the injection system. After the first occurrence of malfunctions, their codes are stored in a memory device. At the same time, a signaling device lights up on the instrument panel, which indicates that a fault code has entered the memory device. Even if the fault occurs only once, for example, due to loose contact, its code is also stored in the memory device.
Issuance of fault codes in the form of a sequence of light pulses
The fault code memory is interrogated by connecting the VAG diagnostic tester to the plug located under the bellows in front of the gear lever. Pay attention to the instructions in the operating instructions for the diagnostic tester.
If a diagnostic tester is not available, interrogation of the memory for fault codes from 4/89 can also be performed using a semiconductor lamp.
Check the fuse no. 18 in the fuse box, replace the fuse if necessary.
Connect a semiconductor diode lamp, for example VAG 1527, as shown in the figure, to the test sockets located in the footwell on the driver's side -A- (black) and -B- (brown).
Start the engine and let it idle. When interrogating the memory device, you must not give gas, otherwise the code in the form of a sequence of light pulses will be erased.
Attention: If the engine does not start due to faults in the injection system, operate the starter for approx. 6 seconds. Without turning off the ignition after that, interrogate the memory device.
Connect auxiliary plugs -C- and -D- for at least 5 seconds and disconnect again. The LED should turn on to flash.
Each code in the form of a sequence of light pulses consists of four groups of light pulses. There are pauses of approximately 2.5 s between groups of light pulses.
Fault codes are read by determining the number (quantities) light pulses within each group.
Read the fault code as a sequence of light pulses and write it down. If a sequence of light pulses in the form of 44-4-4 is issued, then the memory device does not contain fault codes and the test is completed.
If a fault code is issued, it should be recorded. The process of reading fault codes continues until the code 0-0-0-0 appears (end of issuing codes - ENDE). To repeat the process of reading the codes, either insert the fuse in the fuel pump relay for at least 5 seconds, or connect the plugs -C- and -D- for at least 5 seconds.
Determine the fault from the table of fault codes and eliminate it.
Erasing the contents of the memory device for fault codes
Switch off the ignition.
Connect plugs -C- and -D-.
Turn on the ignition and do not turn it off for at least five seconds. In this case, the fault codes in the memory device are erased.
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