Engine Coolant Temperature Sensor 1, Checking

Engine Coolant Temperature Sensor 1, Checking

• 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 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.

Test procedure

- Observe safety precautions. Refer to => [ Safety Precautions ] Safety Precautions

- Observe Clean Working Conditions. Refer to => [ Clean Working Conditions ] Clean Working Conditions

- Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] Preliminary Check

Start diagnosis

- Connect the scan tool.

- Switch the ignition On.

- Using the scan tool, check the coolant temperature:






If indication remains at approx. -40.0° C:

- 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 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 values:






If the specified values were Not obtained:

- Replace the Engine Coolant Temperature (ECT) Sensor (G62) Refer to the Repair Information.

°Testing if display is approx. - 40.0 C

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

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

- Turn the ignition On.

- Check the value indicated on the scan tool display.

If the value jumps to approx. 140.0° C

- Switch the ignition Off.

- Replace the Engine Coolant Temperature (ECT) Sensor (G62) Refer to the Repair Information.

If indication remains at approx. -40.0° C:

Checking wiring

- Remove the 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 Engine Control Module (ECM) (J623) electrical harness connector T60 terminals for an open circuit or a short to voltage, refer to the chart below.






Specified values: 1.5 ohms Max. and 0 volts with key on and ECM disconnected (no short to voltage).

If the specified value was Not obtained:

- Check the wiring for an open or short circuit to Battery (+).

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

- If necessary, repair the faulty wiring connection.

If the specified value was obtained:

- Using a multimeter, check terminal 2 of the ECT sensor to engine ground.

Specified value: 1.5 ohms Max

If the specified value was Not obtained:

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

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

- If necessary, repair the faulty wiring connection.

If the specified value was obtained:

- Replace the Engine Control Module (ECM) (J623). Refer to the Repair Information.

°Testing if display approx. 140.0 C

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

- Turn the ignition switch ON.

If indication jumps to approx. -40.0° C:

- Switch ignition Off.

- Replace the Engine Coolant Temperature (ECT) Sensor (G62) Refer to the Repair Information.

If the value remains at approx. 140.0° C

Checking wiring

- Remove the Engine Control Module (ECM) (J623) and disconnect the ECM connectors. Refer to the Repair Information.

- Disconnect the ECT harness connector at the sensor.

- Using a multimeter, check the signal circuit of the Engine Coolant Temperature (ECT) Sensor (G62) electrical harness connector terminal 1 to engine ground.

Specified value: OL or no continuity.

If the specified value was Not obtained:

- Check the wiring for a short circuit to ground.

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

- If necessary, repair the faulty wiring connection.

If the specified value was obtained:

- Replace the 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 - 09.

2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 09.

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