Coolant Temperature Sensor/Switch (For Computer): Testing and Inspection

Engine Coolant Temperature Sensor, Checking

CAUTION!
• Cooling system is under pressure.

• Danger of scalding when opening!

• Use only gold-plated terminals when servicing terminals in the electrical harness connector of Engine Coolant Temperature (ECT) Sensor (G62).

Special tools, testers and auxiliary items required

• Multimeter.

• jumper wire.

• Wiring diagram.

Test requirements

• The Motronic Engine Control Module (ECM) (J623) fuses OK.

• Battery voltage at least 12.5 volts.

• All electrical consumers such as, lights and rear window defroster, switched off.

• Vehicles with automatic transmission, shift selector lever into position "P" or "N".

• A/C switched off.

• Ground (GND) connections between engine/transmission/chassis OK.

• Ignition switched off.

• Engine cold.

Function test

- Connect the scan tool.

- Switch the ignition on.

- Using the scan tool, check the coolant temperature:





If the specified value is not obtained:

- Continue test according to the following table:





If the specified value was obtained:

- Start the engine and let it run at idle.

The temperature value must increase uniformly in increments of 1.0° C.

If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent.

- Replace the Engine Coolant Temperature (ECT) Sensor (G62).

Procedure

- Remove the rear engine cover - 2 -.





- Loosen clamps and remove the left air duct hose - arrows -.





- Loosen clamps and remove the right air guide hose - arrows -.





- Disconnect the vacuum hose - 1 - from the intake manifold.

- Remove the screws- arrows - and the air duct.





- Disconnect the Engine Coolant Temperature (ECT) Sensor (G62) electrical harness connector - 1 -.





Checking internal resistance

- Using a multimeter, check the Engine Coolant Temperature (ECT) Sensor (G62) terminals 1 to 2 for resistance.





Use the chart below for the specified values:

• Area A: Resistance values 0 to 50° C.

• Area B: Resistance values 50 to 100° C.

Specified values:





• Range A, 30° C equals a resistance of 1.5 to 2.0 kohms

• Range B, 80° C equals a resistance of 275 to 375ohms

If any of the specified values was not obtained:

- Replace the Engine Coolant Temperature (ECT) Sensor (G62).

°Testing if display is approx. - 40.0 C:

- Disconnect the Engine Coolant Temperature (ECT) Sensor (G62) electrical harness connector - 1 -.





- Using a jumper wire, connect the Engine Coolant Temperature (ECT) Sensor (G62) electrical harness connector terminals 1 to 2.

- Check the value indicated on the scan tool display.





If the value jumps to approx. 140.0° C

- End diagnosis and switch the ignition off.

- Replace the Engine Coolant Temperature (ECT) Sensor (G62).

If indication remains at approx. -40.0° C:

°Testing if display approx. 140.0 C:

- Disconnect the Engine Coolant Temperature (ECT) Sensor (G62) electrical harness connector - 1 -.





If indication jumps to approx. -40.0° C:

- End diagnosis and switch ignition off.

- Replace the Engine Coolant Temperature (ECT) Sensor (G62).

If indication remains at approx. 140.0° C:

Checking wiring

If the manufacturers test box is being used. Perform the following step.

- Install the test box.

If the manufacturers test box is not being used. Perform the following step.

- Remove the Motronic Engine Control Module (ECM) (J623). Refer to => [ Engine Control Module, Removing and Installing ] Engine Control Module, Removing and Installing.

- Using a Multimeter, check the Engine Coolant Temperature (ECT) Sensor (G62) electrical harness connector terminals to the Motronic Engine Control Module (ECM) (J623) electrical harness connector T60a terminals for an open circuit according to the wiring diagram.









Specified value: 1.5 ohms Max.

If the specification was not obtained:

- Check the wiring for a short circuit to each other, Battery (+), Ground (GND), or an open circuit.

- If necessary, repair the faulty wiring connection.

If no malfunction is detected in the wiring:

- Replace the Motronic Engine Control Module (ECM) (J623). Refer to => [ Engine Control Module, Removing and Installing ] Engine Control Module, Removing and Installing.

Assembly is performed in the reverse order of removal.

Final procedures

After repair work, the following work steps must be performed in the following sequence:

1. Check the DTC memory. Refer to => [ Diagnostic Mode 03 - Read DTC Memory ] Diagnostic Mode 03 - Read DTC Memory.

2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Mode 04 - Erase DTC Memory.

3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code ] Monitors, Trips, Drive Cycles and Readiness Codes.

- End of diagnosis.