Coolant Temperature Sensor/Switch (For Computer): Testing and Inspection

Engine Coolant Temperature (ECT) Sensor G62, Checking

Special tools, testers and auxiliary items required
- Multimeter V.A.G 1526 or equivalent.
- Test Box 105 Pin VAG1598/42.
- Adapter Lead Vag1598/39 VAG1598/39.
- Adapter cable V.A.G 1598/39-1.
- connector test kit V.A.G 1594 C

NOTE: Use only gold-plated terminals when servicing terminals in harness connector of Engine Coolant Temperature (ECT) Sensor G62.

Test requirements
- Fuses for Engine Control Module (ECM) J623 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.

Function test
- Connect the diagnostic tester.
- Switch ignition on.
- Select "Diagnostic mode 1: Check measured values".
- Select measured value "PID 05: Coolant temperature".
- Check specified value of coolant temperature:







If specified value is not obtained:
- Continue test according to the following table:







If specified value is obtained:
- Start engine and let it run at idle.

Temperature value must increase uniformly in increments of 1.0 degree C.

If the engine shows problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent.
- Replace Engine Coolant Temperature (ECT) Sensor G62.

Testing if display approx. -40.0 degrees C:







- Disconnect the electrical harness connector - 1 - from the Engine Coolant Temperature (ECT) Sensor G62.
- Using adapter cables from connector test kit V.A.G 1594 C , bridge electrical connector terminals 1 + 2 together and observe indication on display.

If indication jumps to approx. 140.0 degrees C:
- End diagnosis and switch ignition off.
- Replace Engine Coolant Temperature (ECT) Sensor G62.

CAUTION:
- Cooling system is under pressure.
- Danger of scalding when opening.

If indication remains at approx. -40.0 degrees C:
- Check the wiring for a short circuit to Battery positive (+) or an open circuit.
- If necessary, repair the wiring connection.
- End diagnosis and switch ignition off.

Testing if display approx. 140.0 degrees C:
Testing if display approx. -40.0 degrees C:







- Disconnect the electrical harness connector - 1 - from the Engine Coolant Temperature (ECT) Sensor G62.

If indication jumps to approx. -40.0 degrees C:
- End diagnosis and switch ignition off.
- Replace Engine Coolant Temperature (ECT) Sensor G62.

CAUTION:
- Cooling system is under pressure.
- Danger of scalding when opening.

- End diagnosis and switch ignition off.

If indication remains at approx. 140.0 degrees C:

Checking wiring
- Connect the Test Box 105 Pin VAG1598/42 to the wiring harness of the Engine Control Module (ECM) J623. The ECM is not connected.







- Using the Test Box 105 Pin VAG1598/42 and Multimeter V.A.G 1526 A or equivalent, check the following wiring connection for an open circuit.

Terminal Test box socket
1 10
2 14

Specified resistance 1.5 Ohms 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 the wiring:







- Using multimeter V.A.G 1526 B or equivalent, check Engine Coolant Temperature (ECT) Sensor G62 electrical connector terminals 1+2 for resistance.
- Area A: Resistance values for temperature range 0 to 50 degrees C.
- Area B: Resistance values for temperature range 50 to 100 degrees C.







Read-out examples:
- 30 degrees C is in range A and corresponds to a resistance of 1.5 to 2.0 k Ohms
- 80 degrees C is in range B and corresponds to a resistance of 275 to 375 Ohms

If the specification is not obtained:
- Replace Engine Coolant Temperature (ECT) Sensor G62.

If the specification is obtained:
- Replace the Engine Control Module (ECM) J623.

Final procedures
After repair work, the following work steps must be performed in the mentioned sequence:
1. Check the DTC memory.
2. If necessary, erase the DTC memory.
3. If the DTC memory was erased, generate readiness code.

- End diagnosis and switch the ignition off.