Signal Too Low

Signal too low

Checking the function of the overheat protection thermostat




- Ignition on.
Activate the heater. Read off the temperature at the overheat protection thermostat.
On activation of the heater sequence, the heater starts up and operates for approximately 2 min 30 s.
Do not interrupt the heater sequence. The heater is switched off automatically after approximately 2 min 30 s.
Check that the temperature rises when activating the heater.
The temperature should cycle between outside temperature -125°C depending on the status of the heater.





Continue - Checking the component and wiring

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Checking the component and wiring








- Ignition off
- Disconnect the connector for the overheat protection thermostat.
Check the terminals. Check for contact resistance. Check for loose connections. Check for oxidation.
Check the resistance of the overheat protection thermostat.
Check the cable between control module terminal #5 and the terminal for the overheat protection thermostat. Check for a short-circuit to ground.
Check the cable between control module terminal #6 and the terminal for the overheat protection thermostat. Check for a short-circuit to ground.
Remedy as necessary.

Other information
- Component specification [1][2]Auxiliary Cabin Heater
- Signal specification Signal Description, Combustion Preheater Module (CPM)
- Overheat protection thermostat/engine coolant temperature sensor, replacing Overheat Protection Thermostat/Engine Coolant Temperature Sensor, 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 heater.
On activation of the heater sequence, the heater starts up and operates for approximately 2 min 30 s.
Do not interrupt the heater sequence. The heater is switched off automatically after approximately 2 min 30 s.
Read off the temperature at the overheat protection thermostat.
Check that the temperature rises when activating the heater. The temperature should cycle between outside temperature -125°C depending on the status of the heater.





Does the temperature rise?

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 function of the overheat protection thermostat

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