Heating Diagnosis, System H 01
Test Points 1-14:
Test Points
Fault, Fault code
Possible causes, elimination, notes
Test point 1
Interface to instrument cluster
Open circuit
Short to ground
Fault code 20
Diagnosis conditions
No control module fault stored.
No fault with supply voltage (terminal 15).
Open circuit
1. Unplug connector B from the heating/air-conditioning control.
2. Unplug connector III from the instrument cluster.
3. Connect ohmmeter to connector B 13 and to connector III pin 26.
Display < 5 ohm
NOTE: The wire is routed via the 12-pole plug connection on the heating/air-conditioning unit.
Short to ground
1. Unplug connector B from the heating/air-conditioning control.
2. Unplug connector Ill from the instrument cluster.
3. Connect ohmmeter to connector B13 and ground.
Display: Infinity ohm
If 0 - 5 ohm is displayed, check wiring harness for pinching and chafing damage.
Test point 2
Outside temperature sensor
Open circuit
Short to ground
Fault code 21
Diagnosis conditions
No control module fault stored.
No fault with supply voltage (5 volts).
Open circuit
1. Unplug connector A from the heating/air-conditioning control.
2. Connect ohmmeter to connectors A 7 and A 12.
Display: approx. 1.2 kohm at 23 °C
3. Unplug connector from the outside temperature sensor.
4. Connect ohmmeter to connector A 7 and pin 1 (connector of outside temperature sensor).
Display: 0 - 5 ohm
5. Connect ohmmeter to connector A 12 and pin 2 (connector of outside temperature sensor).
Display: 0 - 5 ohm
6. Connect voltmeter to connector A 7 and ground. Switch on ignition.
Display: 0 volts
If approx. 5 volts are displayed, check wiring harness for pinching and chafing damage.
Short to ground
1. Unplug connector A from the heating/air-conditioning control.
2. Connect ohmmeter to connector A 7 and ground.
Display: Infinity ohm
If 0 - 5 ohm is displayed, check wiring harness for pinching and chafing damage.
Test point 3
Interior temperature sensor
Open circuit
Short to ground
Fault code 22
Diagnosis conditions
No control module fault stored.
No fault with supply voltage (5 volts).
Outside temperature higher than - 40 °C.
Open circuit
1. Unplug connector A from the heating/air-conditioning control.
2. Connect ohmmeter to connectors A 10 and A 12.
Display: approx. 3 kohm at 23 °C
NOTE: The wires to the interior temperature sensor are routed via two additional plug connections on the heating/air-conditioning control.
3. Unplug connector from the interior temperature sensor.
4. Connect ohmmeter to connector A 10 and interior sensor connector pin 5.
Display: < 5 ohm
5. Connect ohmmeter to connector A 12 and interior sensor connector pin 4.
Display: < 5 ohm
6. Connect voltmeter to connector A 10 and ground. Switch on ignition.
Display: 0 volts
If approx. 5 volts are displayed, check wiring harness for pinching and chafing damage.
Short to ground
1. Unplug connector A from the heating/air-conditioning control.
2. Connect ohmmeter to connector A 7 and ground.
Display: Infinity ohm
If 0 - 5 ohm is displayed, check wiring harness for pinching and chafing damage.
Test point 4
Footwell blower outlet sensor
Open circuit
Short to ground
Fault code 23
Diagnosis conditions
No control module fault stored.
No fault with supply voltage (5 volts).
Outside temperature higher than - 30 °C.
Open circuit
1. Unplug connectors A and B from the heating/air-conditioning control.
2. Connect ohmmeter to connectors A 12 and B 5.
Display: approx. 2.8 kohm at 23 °C
3. Unplug connector from blower outlet sensor.
4. Connect ohmmeter to connector A 12 and blower outlet sensor connector pin 2.
Display: < 5 ohm
5. Connect ohmmeter to connector B 5 and blower outlet sensor connector pin 1.
Display: < 5 ohm
6. Connect voltmeter to connector B 5 and ground.
Switch on ignition.
Display: 0 volts
If approx. 5 volts are displayed, check wiring harness for pinching and chafing damage.
Short to ground
1. Unplug connector B from the heating/air-conditioning control.
2. Connect ohmmeter to connector B 5 and ground.
Display: Infinity ohm
If 0 - 5 ohm is displayed check wiring harness for pinching and chafing damage.
Test point 5
Supply voltage
(terminal 15)
Voltage too high
Voltage too low
Fault code 24
Diagnosis conditions
No control module fault stored.
Voltage too high
Check the alternator.
Voltage too low
1. Check the alternator.
2. Check or charge the battery.
3. Check contact resistance of wire connections.
Test point 6
Supply voltage
(5 volts)
Voltage too high
Voltage too low
Fault code 25
Diagnosis conditions
No control module fault stored.
Voltage too high
1. Unplug connector C from the heating/air-conditioning control.
2. Connect voltmeter to C 8 and ground.
Switch on ignition.
Display: 0 volts
If the battery voltage is displayed, check the wiring harness for pinching and chafing damage.
3. Push on connector C.
4. Connect voltmeter to C 8 and ground.
Switch on ignition.
Display: 5 ± 0.5 volts
If more than 5.5 volts are displayed, replace the heating/air-conditioning control.
Voltage too low
1. Unplug connector C from the heating/air-conditioning control.
2. Unplug all connectors from the valve drive motors.
3. Connect ohmmeter to connector C 8 and ground.
Display: Infinity ohm
If 0 - 5 ohm is displayed, check wiring harness for pinching and chafing damage.
4. Check potentiometer in the drive motors.
Temperature mixing valve:
Connect ohmmeter to pins 1 and 3.
Display: 4 - 5 kohm at 23 °C
Footwell/defrost valve:
Connect ohmmeter to pins 1 and 3.
Display: 4 - 5 kohm at 23 °C
Central valve:
Connect ohmmeter to pins 1 and 3.
Display: 4 - 5 kohm at 23 °C
Outside air/recirculation valve:
Connect ohmmeter to pins 4 and 5.
Display: 4 - 5 kohm at 23 °C
Test point 7
Motor of temperature mixing valve
Signal implausible
Fault code 26
Diagnosis conditions
No control module fault stored.
No fault with supply voltage (5 volts).
Signal implausible
1. Check temperature mixing valve for smooth operation.
2. Unplug connectors A, B, C and D from the heating/air-conditioning control.
3. Unplug connector from the temperature mixing valve drive motor.
4. Connect ohmmeter to connector C 8 and drive motor connector pin 1.
Display: < 5 ohm
Connect ohmmeter to connector B 8 and drive motor connector pin 2.
Display: < 5 ohm
Connect ohmmeter to connector A 12 and drive motor connector pin 3.
Display: < 5 ohm
Connect ohmmeter to connector D 10 and drive motor connector pin 4.
Display: < 5 ohm
Connect ohmmeter to connector D 2 and drive motor connector pin 5.
Display: < 5 ohm
5. Check wire from connector C 8 to drive motor pin 1 for short to B+ and short to ground.
6. Check wire from connector B 8 to drive motor pin 2 for short to B+ and short to ground.
7. Check wire from connector A 12 to drive motor pin 3 for short to B+.
8. Check wire from connector D 10 to drive motor pin 4 for short to B+ and short to ground.
9. Check wire from connector D 2 to drive motor pin 5 for short to B+ and short to ground.
Test point 8
Motor of central valve
Signal implausible
Fault code 27
Diagnosis conditions
No control module fault stored.
No fault with supply voltage (5 volts).
Signal implausible
1. Check central valve for smooth operation.
2. Unplug connectors A, B, C and D from the heating/air-conditioning control.
3. Unplug connector from central valve drive motor.
4. Connect ohmmeter to connector A 12 and drive motor connector pin 1.
Display: < 5 ohm
Connect ohmmeter to connector B 9 and drive motor connector pin 2.
Display: < 5 ohm
Connect ohmmeter to connector C 8 and drive motor connector pin 3.
Display: < 5 ohm
Connect ohmmeter to connector D 4 and drive motor connector pin 4.
Display: < 5 ohm
Connect ohmmeter to connector D 12 and drive motor connector pin 5.
Display: < 5 ohm
5. Check wire from connector A 12 to drive motor pin 1 for short to B+.
6. Check wire from connector B 9 to drive motor pin 2 for short to B+ and short to ground.
7. Check wire from connector C 8 to drive motor pin 3 for short to B+ and short to ground.
8. Check wire from connector D 4 to drive motor pin 4 for short to B+ and short to ground.
9. Check wire from connector D 12 to drive motor pin 5 for short to B+ and short to ground.
Test point 9
Motor of footwell/defrost valve
Signal implausible
Fault code 28
Diagnosis conditions
No control module fault stored.
No fault with supply voltage (5 volts).
Signal implausible
1. Check footwell/defrost valve for smooth operation.
2. Unplug connectors A, B, C and D from the heating/air-conditioning control.
3. Unplug connector from footwell/defrost valve drive motor.
4. Connect ohmmeter to connector C 8 and drive motor connector pin 1.
Display: < 5 ohm
Connect ohmmeter to connector B 10 and drive motor connector pin 2.
Display: < 5 ohm
Connect ohmmeter to connector A 12 and drive motor connector pin 3.
Display: < 5 ohm
Connect ohmmeter to connector D 11 and drive motor connector pin 4.
Display: < 5 ohm
Connect ohmmeter to connector D 3 and drive motor connector pin 5.
Display: < 5 ohm
5. Check wire from connector C 8 to drive motor pin 1 for short to B+ and short to ground.
6. Check wire from connector B 10 to drive motor pin 2 for short to B+ and short to ground.
7. Check wire from connector A 12 to drive motor pin 3 for short to B+.
8. Check wire from connector D 11 to drive motor pin 4 for short to B+ and short to ground.
9. Check wire from connector D 3 to drive motor pin 5 for short to B+ and short to ground.
Test point 10
Motor of outside air/recirculation valve
Signal implausible
Fault code 29
Diagnosis conditions
No control module fault stored.
No fault with supply voltage (5 volts).
Signal implausible
1. Check outside air/recirculation valve for smooth operation.
2. Unplug connectors A B, C and D from the heating/air-conditioning control.
3. Unplug connector from outside air/recirculation valve drive motor.
4. Connect ohmmeter to connector D 13 and drive motor connector pin 1
Display: < 5 ohm
Connect ohmmeter to connector D 5 and drive motor connector pin 2.
Display: < 5 ohm
Connect ohmmeter to connector B 17 and drive motor connector pin 3.
Display: < 5 ohm
Connect ohmmeter to connector C 8 and drive motor connector pin 4.
Display: < 5 ohm
Connect ohmmeter to connector A 12 and drive motor connector pin 5.
Display: < 5 ohm
5. Check wire from connector D 13 to drive motor pin 1 for short to B+ and short to ground.
6. Check wire from connector D 5 to drive motor pin 2 for short to B+ and short to ground.
7. Check wire from connector B 17 to drive motor pin 3 for short to B+ and short to ground.
8. Check wire from connector C 8 to drive motor pin 4 for short to B+ and short to ground.
9. Check wire from connector A 12 to drive motor pin 5 for short to B+ and short to ground.
Test point 11
A/C
Signal implausible
Fault code 30
NOTE: This fault can be determined only during the system test.
Signal implausible
1. Check refrigerant pressure (see Heating and Air Conditioning.) Heating and Air Conditioning
2. Check high/low pressure switch.
Battery positive voltage must be present at terminal 1 on the high/low pressure switch (with ignition on) if there is sufficient refrigerant in the system.
3. Check the heating activation relay.
Battery positive voltage must be present at terminal 87 when the ignition is switched on.
4. Check the air-conditioning compressor relay. Battery positive voltage must be present at terminal 30 (with the ignition on) and the high/low pressure switch actuated. Terminal 31 must be connected to ground.
Battery positive voltage must be present at terminal 86 when the engine is started.
Terminal 85 must be connected to ground when the DME switches on the air-conditioning compressor (7-second delay).
5. Unplug connector D from the heating/air-conditioning control.
6. Unplug the DME (ECM) connector.
7. Connect ohmmeter to D 6 and DME connector pin 69.
Display: < 5 ohm
NOTE: The wire is routed via two plug connections.
8. Remove the air-conditioning compressor relay.
9. Connect ohmmeter to terminal 85 and DME connector pin 62.
Display: < 5 ohm
NOTE: The wire is routed via one plug connection.
Test point 12
Motor of fresh-air blower
Voltage too low
Voltage too high
Fault code 31
Diagnosis conditions
No control module fault stored.
Supply voltage OK.
Nominal blower voltage > 3 volts.
Nominal blower voltage stabilized.
Voltage too low
NOTE: Voltage too low means that the measured blower voltage lies below the nominal blower voltage.
1. Check the heating activation relay.
Battery positive voltage must be present at terminal 87 when the ignition is switched on.
2. Unplug connector C from the heating/air-conditioning control.
3. Connect voltmeter to C 14 (positive) and ground. Switch on ignition.
Display: Battery voltage
4. Push connector C on the heating/air-conditioning control.
5. Connect voltmeter to C 14 (positive) and C 11 (negative).
Maximum blower speed
Display: approx. 12 V
Minimum blower speed
Display: approx. 0 V
6. Connect voltmeter to C 14 (positive) and C 16 (negative).
Maximum blower speed
Display: approx. 5 V
Minimum blower speed
Display: approx. 9 V
7. Check driver.
Connect voltmeter to positive and pin 3 on driver connector.
Display: Battery voltage
Connect voltmeter to positive and pin 1 on driver connector.
Maximum blower speed
Display: approx. 5 V
Minimum blower speed
Display: approx. 9 V
Connect voltmeter to positive and pin 2 on the driver connector.
Maximum blower speed
Display: approx. 12 V
Minimum blower speed
Display: approx. 0 V
8. Check wiring from heating/air-conditioning control to driver for continuity.
9. Check blower motor.
Voltage too high
NOTE: A higher blower voltage can only be caused by a short to ground on the wires to pins 1 or 2 of the driver.
1. Unplug connector C from the heating/air-conditioning control.
2. Unplug connector from the driver.
3. Connect ohmmeter to C 16 and ground.
Display: Infinity ohm
4. Unplug connector from the fan motor.
5. Connect ohmmeter to driver connector pin 2 and ground.
Display: Infinity ohm
Test point 13
Control module
Control module faulty
Fault code 32
Replace the heating/air-conditioning control.
Test point 14
Sun sensor
Short to B+
Short to ground
Fault code 33
Diagnosis conditions
No control module fault stored.
No fault with supply voltage (5 volts).
Short to B+/ Short to ground
1. Remove sun sensor.
2. Remove plug connection from sun sensor.
3. Connect voltmeter on sleeve side to pin 2 (negative) and pin 3 (positive).
Switch on ignition.
Display: approx. 4.5 - 5 volts
If 0 volts is displayed, check wiring to the heating/air-conditioning control A 12 and B 18 for continuity.
Check wiring to the heating/air-conditioning control B 18 for short to ground.
NOTE: The wiring to the heating/air-conditioning unit is routed via two plug connections.
If the wiring is OK, replace the heating/air-conditioning control.
4. Connect ohmmeter to sun sensor pins 2 and 3.
Sun sensor not in darkness
Display: approx. 1.3 Mohm
Sun sensor in darkness
Display: approx. 240 kohm