Engine Coolant Temperature Sensor, Checking: Notes
- 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.
- jumper wire.
- Wiring diagram.
Test requirements
- The Motronic Engine Control Module (ECM) - J220- 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.
Test procedure
-- Perform a preliminary check to verify the customers complaint. Refer to GENERAL DIAGNOSIS .
Start diagnosis
Function test
-- Connect the scan tool.
-- Switch the ignition on.
-- Using the scan tool, check the coolant temperature:
| Diagnostic text | Specified value | |||
|---|---|---|---|---|
| Coolant temperature | Approx. coolant temperature | |||
If the specified value is not obtained:
-- Continue test according to the following table:
| Indicated | Cause | Test |
|---|---|---|
| approx. -40.0° C | Open circuit or short circuit to (B+) | Testing if display is approx. - 40.0° C: |
| approx. 140.0° C | Short circuit to Ground (GND) | Testing if display approx. 140.0° C: |
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-.
Checking internal resistance
-- Disconnect the Engine Coolant Temperature (ECT) Sensor -G62- electrical harness connector -arrow-.
-- 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 kΩ
- Range B, 80° C equals a resistance of 275 to 375Ω
If any of the specified values was not obtained:
-- Replace the Engine Coolant Temperature (ECT) Sensor - G62-.