Test Point 12

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 stabilised.

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