Introduction

General Instructions/Safety Instructions
The following points must be observed during vehicle diagnosis:
- When replacing an air-conditioning control unit, observe the coding for the country area, pollen filter, the AC symbol and the PCM (1).
- After troubleshooting or repairs, erase the fault memory with the Porsche System Tester II No. 9588 and carry out a test drive.
- After the test drive, read out the fault memory with the Porsche System Tester II No. 9588 again.

CAUTION:
Danger of damage due to improper handling of batteries and control unit plug connections.
- Disconnect the battery connection terminals only when the engine is switched off.
- Start the engine only when the battery connection terminals are properly connected.
- Pull off or push on plug connections for the control units or other electronic components only when the ignition is switched off.
- Disconnect the negative terminal of the battery before welding work on the vehicle.

Establishing Communications
Communication between the Porsche System Tester II No. 9588 and the air-conditioning system regulator occurs via the instrument cluster and the CAN comfort bus.

If both CAN comfort leads between air-conditioning system regulator and instrument cluster are open circuit, if there is a short circuit between them or they are interchanged, then no communication is possible between the Porsche System Tester II No. 9588 and the air-conditioning system regulator. For troubleshooting, refer "Air-conditioning CAN Bus off".

General Information On The Fault Memory
- The contents of the fault memory are retained even when the unit is removed.
- Faults in the control unit can only be erased after an "ignition off-on" reset.

Diagnostic Conditions
The fault can only be identified if the requirements listed under diagnostic conditions are met. For this reason, the specified procedure must be observed after a fault is repaired:
1. Clear fault memory.
2. Satisfy the requirements listed under 'Diagnostic conditions'.
3. Read out fault memory again

Possible Causes Of Fault
The possible fault causes that may be responsible for the fault are listed here. Please note that in certain circumstances further faults can be stored in the fault memory after troubleshooting (e.g. if plugs are disconnected). After carrying out repairs, read out the fault memory of all control units and erase any faults.

Diagnosis/Troubleshooting
- The errors entered are indicated using the Porsche fault code and as clear text.
- The fault memory Info key F8 on the Porsche System Tester II No. 9588 can be used to access the extended fault memory. This information should be saved using the F4 key and printed out.

The following information can be displayed:

- Fault type
The following fault types are possible:
- (No details available)
- Short circuit to B+
- Short circuit to ground
- Signal implausible
- No reaction to activation
- Voltage deviation too small
- Voltage deviation too great

- Occurrence of faults
The fault occurred as follows:
- statistically (i.e. once)
- sporadically (i.e. more than once)

- Fault status
The following status types are possible:
- available (at the time of the last diagnosis routine)
- not available (at the time of the last diagnosis routine)