Fault Code 0789

Fault Code 0789

Reversing 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 Porsche System Tester II 9588 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 Porsche System Tester II 9588 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.
- 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 Porsche System Tester II 9588 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.

Work Instruction 1 - 2:

Work Instruction 3 - 6:

2. Troubleshooting only for fault type: Short circuit to B+

Work Instruction 1 - 5: