Engine Coolant Temperature Sensor Checking
Engine Coolant Temperature Sensor 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 (G83).
Special tools, testers and auxiliary items required
• Multimeter.
• Jumper wire.
• Wiring diagram.
• 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 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 the Engine Coolant Temperature (ECT) Sensor (G62). Refer to the Repair Information.
Checking internal resistance
- Disconnect the the Engine Coolant Temperature (ECT) Sensor (G62) electrical harness connector.
- Using a multimeter, check the the Engine Coolant Temperature (ECT) Sensor (G62) terminals 1 to 2 for resistance.
Use the chart below for the specified values:
If any of the specified values was not obtained:
- Replace the the Engine Coolant Temperature (ECT) Sensor (G62). Refer to the Repair Information.
°Testing if display is approx. - 40.0 C:
- Disconnect the the Engine Coolant Temperature (ECT) Sensor (G62) electrical harness connector.
- Using a jumper wire, connect the 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 the Engine Coolant Temperature (ECT) Sensor (G62). Refer to the Repair Information.
If indication remains at approx. -40.0° C:
°Testing if display approx. 140.0 C:
- Disconnect the the Engine Coolant Temperature (ECT) Sensor (G62) electrical harness connector.
- Turn the ignition ON.
If indication jumps to approx. -40.0° C:
- Replace the the Engine Coolant Temperature (ECT) Sensor (G62) Refer to the Repair Information.
- Switch ignition OFF.
If indication remains at approx. 140.0° C:
Checking wiring
- Remove the Engine Control Module (ECM) (J623). Refer to the Repair Information.
- Using a multimeter, check the the Engine Coolant Temperature (ECT) Sensor (G62) electrical harness connector terminals to the Engine Control Module (ECM) (J623) electrical harness connector T94 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 high resistance, an open or a short to voltage or ground.
- 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 the voltage supply was Not OK:
- Replace the Engine Control Module (ECM) (J623). Refer to the Repair Information.
Final procedures
After repair work, the following work steps must be performed in the mentioned 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.