Fault Code 0789
Fault code 0789Reversing light switch
NOTE: The ignition must be switched off and then switched on again in order to display an error message in the instrument cluster.
Use the 'Actual values' menu in the 9588 Porsche System Tester II to check the transmission status and the actual values of the shift solenoid valves and sensors.
Diagnostic conditions
The following requirements are met for at least 0.5 seconds:
- Voltage greater than 10.2 V and less than 15.5 V
- Ignition on
- Internal Tiptronic control module function test was completed successfully
- No fault on multi-function switch
The fault type 'open circuit/short circuit to ground' is stored when the gear 'R' is engaged and the signal of the 'reversing light switch' is 'OFF' for longer than one second.
The fault type 'short circuit to B+' is stored when the gear 'D' is engaged and the signal of the 'reversing light switch' is 'ON' for longer than one second.
Possible causes of fault
NOTE:
The 'Diagnosis/troubleshooting' shown below is adapted to suit the fault type displayed in the tester (please note fault type numbering 1, 2,... etc..). The fault memory Info key [F8] on the 9588 Porsche System Tester II can be used to read out the fault type in the 'extended fault memory'.
- 1. 'Open circuit/short circuit to ground'
- 2. 'Short circuit to B+'
Affected pins
Tiptronic control module plug:
- Pin 21 'reversing light input', from vehicle electrical system control unit 'pin A20' (see Wiring diagram - Vehicle electrical system control unit 'SHG1')
Diagnosis/troubleshooting G 0210
NOTE:
Visual inspection: In the next troubleshooting section, please check first that the affected 'pins' on the Tiptronic control module plug connection and the 'pins' on the 'existing transmission wiring' plug connection are neither damaged nor corroded. Remove any soiling or corrosion/oxidation. Replace damaged parts/wires.
NOTE:
Control unit replacement: Before replacing the 'Tiptronic control unit', the ground connections, power supply and plug connections on the control unit must be checked as OK. Please observe the coding of the control module. After the test drive, read out the fault memory with the 9588 Porsche System Tester II again. Additional causes of faults that could damage the 'Tiptronic control module' should be detected and remedied.
1. Troubleshooting only for fault type: 'Open circuit/short circuit to ground'
NOTE: The multi-function switch is protected by fuse '52' in the fuse carrier at the right of the dashboard. This fuse should be checked for continuity and replaced if not OK.
2. Troubleshooting only for fault type: 'Short circuit to B+'
