Signal Too High

Signal too high

Checking the status




- Ignition on.
Activate the combustion fan.
There must be a buzzing sound from the combustion fan when it is activated.
The fault is permanent if the combustion fan does not start.
If the combustion fan starts, this is an indication that the fault was present previously but that it is not active at the moment, i.e. the fault is intermittent.





Continue - Checking the component and wiring

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Checking the component and wiring








- Ignition off
- Disconnect the connector in the heater.
Check the terminals. Check for contact resistance. Check for loose connections. Check for oxidation.
Check that the fan wheel for the combustion fan is not jammed or sticking and that it can rotate without resistance.
Check the cable between combustion preheater module (CPM) terminal #13 and the combustion fan terminal. Check for a short-circuit to supply voltage.
Check the cable between combustion preheater module (CPM) terminal #14 and the combustion fan terminal. Check for a short-circuit to supply voltage.
Remedy as necessary.

Other information
- Signal specification Signal Description, Combustion Preheater Module (CPM)
- Component specification [1][2]Auxiliary Cabin Heater
- Blower fan motor engine coolant heater, replacing Blower Fan Motor Engine Coolant Heater, Replacing
- Checking wiring and terminals Checking Wiring and Terminals









Continue - Verification

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Verification




Verification

Hint: After carrying out the repair, check that the fault has been remedied.








- Ignition off
- Reinstall the connectors, components etc.
- Ignition on.
Activate the combustion fan.
There must be a buzzing sound from the combustion fan when it is activated.





Does the combustion fan start?

Yes - Troubleshooting procedure complete

No - Fault-tracing information

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Fault-tracing information




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 component and wiring

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