Signal Too High / Signal Missing
Signal too high / Signal missing
Checking the fan motor and the passenger compartment temperature sensor
- Ignition on
- Check that the fan is functioning. Place a small, thin piece of paper in front of the ventilation grille for the passenger compartment temperature sensor.
If the paper is sucked against the grille, the fan is working.
Note! The fan is only activated at passenger compartment temperatures in excess of -10 °C (14 °F).
Is the fan working?
Yes - Checking connectors and wiring
No - Checking components and connectors
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Checking components and connectors
- Ignition off
- Disconnect the climate control module (CCM).
Check that the fan rotates freely and is not blocked by any objects.
Check the fan connector. Check for contact resistance and oxidation.
Note! From and including w50 2001, the fan is connected directly to connector C with no wiring in-between.
Try replacing the fan if no other fault is found.
Remedy as necessary.
Other information:
- To access and replace the control module, see Climate control module (CCM), replacing Service and Repair
- To access or replace the blower fan motor, see Blower fan motor passenger compartment temperature sensor, replacing Service and Repair
- For other values, see Signal specification Signal Specification
- Checking wiring and terminals Checking Wiring And Terminals.
Continue - Checking connectors and wiring
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Checking connectors and wiring
Note! From and including w50 2001, the fan is connected directly to connector C with no wiring in-between.
Check the wiring between the climate control module (CCM) and fan motor. Check for an intermittent short-circuit to ground and supply voltage.
Check the wiring for the control module. Check for an intermittent open-circuit.
Check connector C. Check for contact resistance and loose connections.
Other information:
- To access and replace the control module, see Climate control module (CCM), replacing Service and Repair
- To access or replace the blower fan motor, see Blower fan motor passenger compartment temperature sensor, replacing Service and Repair
- For other values, see Signal specification Signal Specification
- Checking wiring and terminals Checking Wiring And Terminals.
Continue - Verification
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Verification
Hint: After carrying out the repair, check that the fault has been remedied.
- Ignition off
- Reinstall the connectors, components etc.
- Ignition on
- Use a thin piece of paper in front of the fan to see whether the fan is blowing (on the reverse of the control module).
The fan is functioning if the paper moves.
Is the fan working?
Yes - VERIFIED
No - VERIFICATION FAILED
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VERIFIED - FAULT FOUND
VERIFICATION FAILED - Fault-tracing information
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Information
Fault-tracing information
The fault should have been detected and remedied. As this is not the case fault-tracing has failed.
Exit fault-tracing for this diagnostic trouble code (DTC) or make another attempt.
Do you want to exit fault-tracing?
Yes - Exit fault-tracing
No - Attempt New Test
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Attempt New Test - Checking the fan motor and the passenger compartment temperature sensor
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Information
Fault-tracing information
If the fault is intermittent, do not verify fault-tracing if the fault does not recur.
It is possible to view the information again, or leave fault-tracing for this diagnostic trouble code (DTC).
Do you want to view the information again?
Yes - Attempt New Test
No - FAULT FOUND
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Attempt New Test - Checking the fan motor and the passenger compartment temperature sensor
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