Test Points
Test Points
Fault, fault code
Possible causes, elimination, notes
Test point 1
Data lead, air conditioner -PCM
Open circuit/short to ground
Short to B+ Signal disturbance
Fault code 20
Open circuit/short to ground
1. Pull off plug II on the display and operator control unit.
2. Pull off plug C on the heater / A/C control unit.
3. Check lead from plug II pin 15 to plug C 12 for continuity and short to ground.
NOTE: The lead is routed via the 10-pole plug connection on the heater/ A/C unit.
Short to B+
1. Pull oft plug II on the display and operator control unit.
2. Pull oft plug C on the heater / A/C control unit.
3. Check lead from plug II pin 15 to plug C 12 for short to B+.
Signal disturbance
Check wiring harness for short with other leads.
Test point 2
Data lead, navigation unit-PCM
Open circuit/short to ground
Short to B+ Signal disturbance
Fault code 21
Open circuit/short to ground
1. Pull off plug II on the display and operator control unit.
2. Pull off plug on the navigation unit.
3. Check lead from navigation unit plug pin 7 to plug II pin 17 for continuity and short to ground.
Short to B+
1. Pull off plug II on the display and operator control unit.
2. Pull off plug on the navigation unit.
3. Check lead from navigation unit plug pin 7 to plug II pin 17 for short to B+.
Signal disturbance
Check lead from navigation unit plug pin 7 to plug II pin 17 for short with other leads.
Test point 3
Data lead, PCM-navigation unit
Short to ground
Short to B+
Fault code 22
Short to ground
1. Pull off plug II on the display and operator control unit.
2. Pull off plug on the navigation unit.
3. Check lead from navigation unit plug pin 5 to plug II pin 4 for short to ground.
Short to B+
1. Pull off plug II on the display and operator control unit.
2. Pull off plug on the navigation unit.
3. Check lead from navigation unit plug pin 5 to plug II pin 4 for short to B+.
Test point 4
Data lead, DSP-PCM
Open circuit/short to ground
Short to B+
Signal disturbance
Fault code 23
Open circuit/short to ground
1. Pull off plug II on the display and operator control unit.
2. Pull off plug I (18-pole) on the amplifier.
3. Check lead from plug II pin 14 to plug I pin 17 for continuity and short to ground.
Short to B+
1. Pull off plug II on the display and operator control unit.
2. Pull off plug I (18-pole) on the amplifier.
3. Check lead from plug II pin 14 to plug I pin 17 for short to B+.
Signal disturbance
Check lead from plug II pin 14 to plug I pin 17 for short with other leads.
Test point 5
Speedometer A, navigation unit
Open circuit/short to ground/short to B+
Fault code 24
Open circuit/short to ground/short to B+
1. Pull off plug on the navigation unit.
2. Pull off plug I on the instrument cluster.
3. Check lead from navigation unit plug pin 3 to plug I pin 13 for continuity and short to ground or short to B+.
NOTE: The lead is routed via jumper plug 1 on relay carrier 1.
Test point 6
Signal, reverse gear-navigation unit
Signal implausible
Fault code 25
Signal implausible
1. Check reversing light switch or, on Tiptronic vehicles, position switch.
2. Check lead from navigation unit plug pin 4 to the reversing light switch or position switch for short circuit to B+.
NOTE: The lead is routed via plug connection X 2/4 and via the jumper plug 20/1 on relay carrier 2.
Test point 7
Antenna, navigation unit
Open circuit
Fault code 26
Open circuit
1. Check whether plug connection of the antenna lead is securely locked.
2. Check whether plug connection of the antenna lead on the navigation unit is securely locked.
3. Check continuity of the antenna lead.
Test point 8
Data lead, PCM-instrument cluster
Short to ground
Short to B+
Fault code 27
Short to ground
1. Pull off plug I on the display and operator control unit.
2. Pull off plug III on the instrument cluster.
3. Check lead from plug I pin 20 to plug III pin 6 for short to ground.
Short to B+
1. Pull off plug I on the display and operator control unit.
2. Pull off plug III on the instrument cluster.
3. Check lead from plug I pin 20 to plug III pin 6 for short B+.
Test point 9
Data lead, instrument cluster-PCM
Open circuit/short to B+
Short to ground
Signal disturbance
Fault code 28
Open circuit/short to B+
1. Pull off plug I on the display and operator control unit.
2. Pull off plug III on the instrument cluster.
3. Check lead from plug I pin 21 to plug III pin 11 for continuity and short to B+.
Short to ground
1. Pull off plug I on the display and operator control unit.
2. Pull off plug III on the instrument cluster.
3. Check lead from plug I pin 21 to plug III pin 11 for short to ground.
Signal disturbance
Check lead from plug I pin 21 to plug III pin 11 for short with other leads.
Test point 10
Vehicle data record
Programming error
Fault code 29
1. Select menu item Modify coding.
2. Select Vehicle model.
3. Modify coding from LHD vehicle (RHD vehicle) to RHD vehicle (LHD vehicle).
4. Modify coding from RHD vehicle (LHD vehicle) to LHD vehicle (RHD vehicle).
If the fault appears again, replace the display and operator control unit.
Test point 11
Program memory
Programming error
Fault code 30
1. Remove CD from navigation unit.
2. Switch off PCM.
3. Switch on PCM and insert CD.
4. Clear fault memory.
5. Read out fault memory
If the fault appears again, insert a different CD (older version).
6. Switch off PCM.
7. Switch on PCM.
8. Clear fault memory.
9. Read out fault memory
If the fault appears again, replace the display and operator control unit.
Test point 12
Signal, terminal 15 PCM
Open circuit
Fault code 31
NOTE: This fault is stored only if the vehicle is driven faster than 50 km/h for more than 10 seconds.
1. Check fuse E 8.
2. Pull off plug II on the display and operator control unit.
3. Connect voltmeter to plug II pin 2 (positive) and ground. Switch on ignition. Display: Battery voltage.
Test point 13
Signal, terminal 86 s PCM
Open circuit
Fault code 32
NOTE: This fault is stored only if the ignition is switched on for at least 1 minute.
1. Check fuse E 1.
2. Pull off plug II on the display and operator control unit.
3. Connect voltmeter to plug II pin 3 (positive) and ground. Switch on ignition. Display: Battery voltage.
NOTE: The lead is routed via jumper plug 13/1 on relay carrier 1.
Test point 14
Navigation, CD fault CM faulty/navigation unit
Value range
Fault code 33
Replace navigation unit.
Test point 15
Navigation fault, gyro CM faulty/navigation unit
Value range
Fault code 34
Replace navigation unit.
Test point 16
Connection to audio module
Value range
Fault code 35
Replace display and operator control unit.
Test point 17
Telephone, internal fault
Value range
Fault code 36
Replace display and operator control unit.
Test point 18
Connection to telephone
Value range
Fault code 37
Replace display and operator control unit.
Test point 19
Write error, Flash
Value range
Fault code 38
Replace display and operator control unit.
Test point 20
Video interface
Value range
Fault code 39
Replace display and operator control unit.
Test point 21
Fault, memory interface
Value range
Fault code 40
Replace display and operator control unit.
Test point 22
Fault, photo sensor
Control module faulty
Value range
Fault code 41
Replace display and operator control unit.