Checking Engine Coolant Temperature Sensor

CHECKING ENGINE COOLANT TEMPERATURE SENSOR





Condition

- Diagnostic Trouble Codes (DTCs) in Motronic 4.4 absent.
- Diagnostic trouble codes (DTCs) in AW 50-42 absent.
- Engine at normal operating temperature.
- The fault is permanent.

Possible Source

- Faulty sensor signals.





Check Engine Coolant Temperature

- START the engine and idle it.
- Read off Engine Coolant Temperature (ECT).

Engine coolant temperature (ECT) should be approx. 80° to 105°C (176° to 221°F), at normal operating temperature.

If reading is OK:
- Proceed to Checking Timing Retardation Due to Knock section.

If reading is incorrect:
- Proceed to test step below.





Check Engine Coolant Temperature Sensor Signal

WARNING! Before fault-tracing, disconnect Engine Cooling Fan (FC) Relay connector A so that the engine cooling fan (FC) will not run. Diagnostic trouble code (DTC) EFI-514 engine cooling fan (FC) low-speed, signal may be stored. After fault-tracing the connecter must be reconnected.

- Connect multimeter 999 6525 with temperature box 999 5281 and temperature sensor 999 5282.
- Carefully remove the expansion tank cover.

WARNING! The water may be extremely hot.

- Clamp the hose between the radiator and thermostat housing using a hose clip and disconnect the hose from the thermostat housing.
- Insert sensor in thermostat housing and reinstall hose.
- Remove hose clip.
- Go into scrolling values list.
- START engine and run to normal operating temperature.
- The engine should be warm enough for the thermostat to open.
- Check that the engine coolant temperature (ECT) is within bounds.

Is the temperature within bounds?

Yes:
- Check the engine cooling system.
- If there are no faults proceed to Checking Timing Retardation Due to Knock section.

No:
- Replace the Engine Coolant Temperature (ECT) Sensor.