Signal Too Low
Signal too low
Checking water flow
Check if the lines to and from the heater are blocked or if the heater is damaged so that through flow is restricted in some way.
Remedy as necessary.
Was a fault detected?
Yes - Verification
No - Checking coolant temperature sensor
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Checking coolant temperature sensor
- Start engine.
- Read off coolant temperature in the heater.
Check the engine coolant temperature (ECT) reading is correct. Compare with the actual coolant temperature of the engine.
Is the temperature reading OK?
Yes - Checking component and cables
No - Checking component and cables
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Checking component and cables
Check engine coolant temperature sensor resistance. For resistance values, see Component resistance values Component Resistance Values.
Remedy as necessary.
Other information:
- To access/replace Coolant temperature sensor see Replacing overheat protection, thermostat flame sensor and coolant temperature sensor Service and Repair.
- For other values, see Signal specification Additional heater 912-D/B Signal Specification Additional Heater 912-D/B.
Continue - Verification
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Checking component and cables
Check fuel pump (FP) and control module connector for contact resistance and oxidation according to Checking wiring and terminals. Permanent fault Checking Wiring and Terminals. Permanent Fault.
Check cable between control module #13 and fuel pump (FP) terminal 1 for an intermittent open-circuit according to Checking wiring and terminals. Intermittent faults Checking Wiring and Terminals. Intermittent Faults.
Check cable between control module #11 and fuel pump (FP) terminal 2 for an intermittent open-circuit according to Checking wiring and terminals. Intermittent faults Checking Wiring and Terminals. Intermittent Faults.
Note! Diagnostic trouble code (DTC) HEA-815 Combustion fan signal and/or diagnostic trouble code (DTC) HEA-822 water pump signal is stored if there is a fault in the power cable.
Remedy as necessary.
Other information:
- To access the control module/connect breakout box see.
- To access/replace the fuel pump (FP) see Replacing fuel pump Service and Repair.
- To access/replace the overheat protection thermostat see Replacing overheat protection, thermostat flame sensor and coolant temperature sensor Service and Repair.
Continue - Verification
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Verification
Verification
Hint: After carrying out the repair, check that the fault has been remedied.
- Ignition off.
- Reinstall connectors, components etc.
- Ignition on.
- Activate heater.
Check heater function according to Test driving of Additional heater/Parking heater Initial Inspection and Diagnostic Overview.
Does the heater function?
Yes - VERIFIED
No - VERIFICATION FAILED
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VERIFICATION FAILED - Fault-tracing information
VERIFIED - FAULT FOUND
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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 water flow
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