Engine - Coolant Temperature Sensor/Switch: Testing and Inspection
Engine Coolant Temperature Sensor, Checking
Special tools, testers and auxiliary items required
• Multimeter (VAG1526) or Multimeter (VAG1715)
• Connector test kit (VAG1594)
• Wiring diagram
Test Prerequisites
• The respective fuses of Engine Control Module (ECM) (J623) must be OK:
• The parking brake button must be engaged in order to connect the electrical parking brake.
• Engine must be cold.
Function Test
- Connect diagnostic tester.
- Switch ignition on.
- Under address word 33, select "Diagnostic mode 1: Checking measured values."
- Select measuring value "PID 05: Coolant temperature".
- Check specified value of coolant temperature:
If specified value is obtained:
- Start engine and let run at idle.
Specified value: Temperature value must rise evenly
• The temperature increases 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 and the sensor should be replaced.
• Engine Coolant Temperature (ECT) Sensor (G62) is a temperature dependent resistance. If e.g. moisture in a harness connector leads to a false sensor signal (effect is like resistance connected in parallel), this falsification can still be in a range that is not recognized by the control module.
• If a malfunction regarding Engine Coolant Temperature (ECT) Sensor is stored, control module operates with a calculated replacement value.
If no realistic indication follows:
- Disconnect connector from Engine Coolant Temperature (ECT) Sensor (G62).
- Use adapter cables from connector test kit (VAG1594) to connect portable multimeter (VAG1526) to terminals 1 and 2 of sensor for resistance measurement.
Read-out examples:
Range A displays resistance values for the temperature range of 0 to 50 °C, range B displays resistance values for the temperature range of 50 to 100 °C.
• 30 °C corresponds to a resistance of 1500 to 2000 ohms
• 80 °C corresponds to a resistance of 275 to 375 ohms
If specified value is not obtained, replace engine coolant temperature sensor.
- Read readiness code => [ Readiness Code, Reading ] Monitors, Trips, Drive Cycles and Readiness Codes. If DTC memory was erased, readiness code must be generated again => [ Readiness Code, Generating ] Monitors, Trips, Drive Cycles and Readiness Codes
If specified value is obtained:
- Connect test box (VAG1598/31) to wiring harness of Engine Control Module (ECM).
- Disconnect connector from Engine Coolant Temperature (ECT) Sensor.
The following wire connections must be checked for short circuit to B+, Ground (GND) and for open circuit
- Repair open circuit in wiring or short circuit if necessary.
- In addition, check both wires to each other for short circuit.
Specified value: infinite ohms (no continuity)
If no malfunction is found in wires:
- If no malfunction was recognized for the previous tests.
- Replace Engine Control Module (ECM).
- Read readiness code => [ Readiness Code, Reading ] Monitors, Trips, Drive Cycles and Readiness Codes. If DTC memory was erased, readiness code must be generated again => [ Readiness Code, Generating ] Monitors, Trips, Drive Cycles and Readiness Codes.