Engine Coolant Temperature Sensor, Checking

Engine Coolant Temperature Sensor, Checking

Recommended Special Tools, Workshop Equipment, Testers, Measuring Instruments and Auxiliary Items
- V.A.G 1526 portable multimeter or V.A.G 1715 multimeter
- Adapter set V. A. G 1594
- Wiring diagram

Test Conditions
- The corresponding fuses of Motronic Engine Control Module (ECM) -J220- must be OK
- The parking brake must be applied, otherwise the daytime running lights are switched on.
- Engine must be cold.

Function Test
- Connect diagnostic tester. Diagnostic Tester, Connecting
- Switch ignition on.
- Under address word 33, select "Diagnostic mode 1: Checking measuring values."
- Select the measuring value "PID 05: Coolant temperature".
- Check specified value of coolant temperature:







If the specification is not obtained:
- Perform the test according to the following table:







1) If a temperature is displayed that deviates strongly from the sensor ambient temperature, check sensor wires for contact resistance.

If the specification is obtained:
- Start the engine and run at idle speed.

The temperature value must increase steadily

NOTE:
- Temperature increases in increments of 1.0 degree C.
- if the engine shows problems in certain temperature ranges and the temperature does not climb uniformly, the temperature signal is intermittent and the sensor must be replaced.

Continuation of Test If Display Shows Approx. -40 degrees C:
- Disconnect connector at Engine Coolant Temperature (ECT) Sensor.

Coolant temperature sensor with square connector:







- Bridge terminals 1 + 3 of connector using the corresponding adapter cables and observe the indication on display.

Coolant temperature sensor with oval connector:







- Bridge terminals 3+4 of connector using the corresponding adapter cables and observe the indication on display.

All Vehicles

If display jumps to approx. 143 degrees C:
- End diagnosis and switch ignition off.
- Replace Engine Coolant Temperature (ECT) Sensor -G62- with Engine Coolant Temperature (ECT) Gauge Sensor -G2-.
- Erase DTC memory of ECM. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Generate Readiness Code

If display stays at approx. -40 degrees C:
- End diagnosis and switch ignition off.
- Check wiring according to wiring diagram.

Continuation of Test If Display Shows Approx. 143 degrees C:
- Disconnect 4-pin connector -1 - from Engine Coolant Temperature (ECT) Sensor -G62- (- 2 -).

If display jumps to approx. -40 degrees C:
- End diagnosis and switch ignition off.
- Replace Engine Coolant Temperature (ECT) Sensor -G62- with Engine Coolant Temperature (ECT) Gauge Sensor -G2-.
- Erase DTC memory of ECM. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Generate Readiness Code

If display stays at approx. 143 degrees C:
- End diagnosis and switch ignition off.
- Check wiring according to wiring diagram.

Checking Wiring
- Connect test box to control module wiring harness. Test Box, Connecting For Wiring Test

Coolant temperature sensor with square connector:
- Check wires between test box and 4-pin connector for open circuit according to wiring diagram.

Terminal 1 + Socket 108
Terminal 3 + Socket 93







Wiring resistance: max. 1.5 Ohms

Coolant temperature sensor with oval connector:
- Check wires between test box and 4-pin connector for open circuit according to wiring diagram.

Terminal 3 + Socket 108

Terminal 4 + Socket 93







Wiring resistance: max. 1.5 Ohms

All vehicles
- Also check wires for short circuit to each other, to vehicle Ground (GND) and to B+.

Specification: Infinity Ohms

If no fault is detected in the wiring:

Coolant temperature sensor with square connector:







- Connect multimeter between terminal 1 and 3 of sensor for resistance measurement.

Coolant temperature sensor with oval connector:







- Connect multimeter between terminal 3 and 4 of sensor for resistance measurement.

All vehicles
Area A shows resistance values for temperature range 0 to 50 degrees C, area B shows values for temperature range 50 to 100 degrees C.







Example:
- 30 degrees C corresponds to a resistance of 1500 to 2000 Ohms
- 80 degrees C corresponds to a resistance of 275 to 375 Ohms

If the specification is not obtained:
- Replace Engine Coolant Temperature (ECT) Sensor -G62- with Engine Coolant Temperature (ECT) Gauge Sensor -G2-.
- Erase DTC memory of ECM. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Generate Readiness Code

If no malfunctions are detected in the wires and the resistance values are OK:
- Replace Motronic Engine Control Module (ECM) -J220-.