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3.4 CIS-E Motronic Fault Diagnosis

The CIS-E Motronic engine management system features built-in electronic fault diagnosis which detects faults in the system during normal operation. When activated, the system displays faults as a number code which corresponds to a particular component or function of the system which should be checked.

Your authorized Volkswagen dealer Service Department is equipped with an analyzer which plugs into a special diagnostic connection in the car's wiring harness. It can retrieve and interpret the fault codes, and also perform electronic checks of the differential pressure regulator, the evaporative emission control system, the idle stabilizer valve, and the cold-start valve. The analyzer and diagnostic connectors are shown in Fig. 3-1.

This electronic check of the system is strongly recommended by Volkswagen as the first step in any CIS-E Motronic troubleshooting. It is most certainly recommended for any car that is still protected by Volkswagen's extensive warranty coverage. For the do-it-yourselfer, it is probably the best, most efficient way to quickly and easily diagnose a problem at a nominal cost.

Fig. 3-1. Models with CIS-E Motronic are equipped with on-board diagnostics. Volkswagen dealer's analyzer (VAG 1551) connects to diagnostic connectors located under shifter boot.

System faults related to emissions or safety are stored in permanent memory and must be deliberately erased after the faults are corrected. Additional faults may be recognized by the control unit and stored in temporary memory. The temporary memory is retained whenever the ignition is switched off, but deleted the next time the engine is started.


On California cars, emissions-related faults stored in memory will illuminate the "CHECK" light located to the right of the instrument panel.

The diagnostic connectors can also be used to activate the memory and display faults by flashing the codes on an LED test light. First make sure that fuses 15 (engine electronics), 18 (fuel pump, oxygen sensor) and 21 (interior lights) are OK, that the air conditioning is switched off, and that the engine ground strap located near the ignition distributor is intact and making a good connection. Use the procedure below to access the stored fault codes.

To read stored Motronic fault codes:
1. Test drive the car for at least five minutes.


During the test drive, engine speed should exceed 3000 rpm at least once, the accelerator should be fully depressed at least once, and the engine should be allowed to reach normal operating temperature-176°F (80°C).

2. Without shutting the engine off, let it run at idle for at least two minutes.


If the engine will not start for a test drive, operate the starter for at least six seconds.

3. Switch off the ignition.
4. Connect an LED test light to the diagnostic connectors as shown in Fig 3-2.

Fig. 3-2. Connection of LED test light and jumper wire to Motronic diagnostic connectors (under shifter boot) used to display fault codes.

5. Switch the ignition on.
6. The fault code is displayed by the flashing LED. To display the first fault code, connect the jumper wire as shown in Fig. 3-2 for at least four seconds, then remove it. The LED will flash indicating a four-digit code.
7. To display the next code in the sequence, connect the jumper wire for another four seconds.
8. Repeat until all stored fault codes have been displayed. Then connect the jumper wire once again for at least four seconds. This will erase the permanent fault memory.

Each sequence of flashes indicates one digit of the fault code. For example, two flashes, a pause, three flashes, a pause, one flash, a pause, and two more flashes indicates the code 2-3-1-2. Table c lists the fault codes and what they mean.

Table c. Motronic Diagnostic Codes

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