Engine Coolant Temperature Sensor, Checking

Engine Coolant Temperature Sensor, Checking

Observe all safety precautions: => [ Safety Precautions ] Safety Precautions

View clean working conditions: => [ Clean Working Conditions ] Clean Working Conditions

Prior to repair work, perform a preliminary check to verify the condition. Refer to => [ Preliminary Check ] Preliminary Check.


• 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 connections between engine/transmission/chassis OK.

• Ignition switched off.

• Engine cold.

Start diagnosis

Engine must be at room temperature.

- Connect the scan tool.

- Switch the ignition on.

- Using the scan tool, check the coolant temperature:






If the specified value was obtained:

- Start the engine and let it run at idle.

The temperature value must increase uniformly in increments of approximately 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 the Engine Coolant Temperature (ECT) Sensor (G62). Refer to the repair information.

Checking internal resistance

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

- 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:

Specified value:






If the specified values were Not obtained:

- Replace the Engine Coolant Temperature (ECT) Sensor (G62). Refer to the repair information.

If the specified values were obtained:

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 the repair information.

- 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 T60 terminals for a circuit fault, refer to the chart below.






Specified values: 1.5 ohms Max.

If the specified value was Not obtained:

- Check the wiring for an open, high resistance or short circuit.

- Check the electrical harness connector for damage, corrosion, loose or broken terminals.

- If necessary, repair the faulty wiring connection.

If no malfunction is detected in the wiring and sensor resistance is OK:

- Replace the Motronic Engine Control Module (ECM) (J623). Refer to the repair information.

Final procedures

After the 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 Modes 01 - 0A.

2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 0A.

3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code ] Readiness Code.