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 -G62-.
Special tools and workshop equipment required
- Multimeter.
- Wiring diagram.
Test Requirements
- The Engine Control Module (ECM) -J623- fuses OK.
- Battery voltage at least 12.5 V.
- 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.
Test Procedure
-- Perform a preliminary check to verify the customer's complaint. Refer to PRELIMINARY CHECK .
-- Connect the scan tool.
-- Switch the ignition on.
-- Using the scan tool, check the coolant temperature:
| Diagnostic text | Specified value | |||
|---|---|---|---|---|
| Coolant temperature | approx. ambient temperature | |||
If a temperature is indicated which differs greatly from the ambient temperature of the sensor, check the sensor and wiring for contact resistances and open circuits.
If the specified value is obtained:
-- Start the engine and let it run at idle.
The temperature value must increase uniformly in increments of 10 °C.
If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent and the sensor should be replaced.
-- Replace the the Engine Coolant Temperature (ECT) Sensor - G62-. Refer to ENGINE COOLANT TEMPERATURE SENSOR .
-- End diagnosis and switch the ignition off.
If the indications do not resemble description:
Checking internal resistance
-- Disconnect electrical harness connector -1- from the Engine Coolant Temperature (ECT) Sensor -G62-.
-- Using a multimeter, check the Engine Coolant Temperature (ECT) Sensor -G62- for resistance between terminals -1- and -2-.
Specified value: 450 to 1000 Ω.
If specified value is not obtained:
-- Replace the the Engine Coolant Temperature (ECT) Sensor - G62-. Refer to ENGINE COOLANT TEMPERATURE SENSOR .
If specified value is obtained:
Checking voltage
-- Using a Multimeter --, check the Engine Coolant Temperature (ECT) SensorG62 electrical harness connector for voltage.
| Engine Coolant Temperature (ECT) SensorG62Harness Connector Terminals | Specified Value |
|---|---|
| 1 to 2 | Battery positive (+) |
Specified value: Battery voltage.
If specified value is obtained:
-- Replace the Engine Coolant Temperature (ECT) Sensor -G62-. Refer to ENGINE COOLANT TEMPERATURE SENSOR .
If the specified value was not obtained:
Checking wiring connections
If the manufacturers test box is being used, perform the following step.
-- Connect the Test Box 105 Pin VAG1598/42 with Adapter Cable1598/39-1. Refer to Component Locations Overview .
If the manufacturers test box is not being used, perform the following step.
-- Remove the Engine Control Module (ECM) -J623-. Refer to ENGINE CONTROL MODULE, REPLACING .
-- 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 terminals for resistance.
| Engine Coolant Temperature (ECT) Sensor G62Harness Connector Terminal | Engine Control Module (ECM)J623 |
|---|---|
| 1 | 40 |
| 2 | 43 |
Specified value: 1.5 Ω max.
If the specification is not obtained:
-- Check the wiring for a short circuit to Battery positive (+) or an open circuit.
-- If necessary, repair the wiring connection.
If no malfunctions are found in wires:
-- Replace the Engine Control Module (ECM) -J623-. Refer to ENGINE CONTROL MODULE, REPLACING .
-- Assembly is performed in the reverse of the removal.
After repair work, the following work steps must be performed in the following sequence:
- Check the DTC memory. Refer to DIAGNOSTIC MODE 03 - READ DTC MEMORY .
- If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
- If the DTC memory was erased, generate readiness code. Refer to READINESS CODE .