Engine - Coolant Temperature Sensor/Switch: Testing and Inspection

Diagnostic Procedures


Engine Coolant Temperature Sensor, Checking

• Use only gold-plated terminals when servicing terminals in harness connector.

Special tools, testers and auxiliary items required

• Multimeter (VAG1526) or Multimeter (VAG1715)

• Connector test kit (VAG1594)

• Wiring diagram

Test Prerequisites

• Fuses in E-box (plenum chamber, left) must be OK:





• For vehicles with automatic transmission, selector lever must be in P.

• Battery voltage must be at least 11.5 volts.

• Ground (GND) connections between engine and chassis must be OK.

• Engine must be cold.

Function Test

- Connect diagnostic tester.

- Switch ignition on.

- Under address word 33, select "Diagnostic mode 1: Check measured values."

- Select the measuring value "PID 05: Coolant temperature".

- Check specified value of coolant temperature:





If specified value is not obtained:

- End diagnosis and switch ignition off.

- Control Module Wires, Checking.

If specified value is obtained:

- Start engine and let run at idle.

- Check specified value of coolant temperature at idle:





• 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.

- Switch ignition off.

Control Module Wires, Checking

- Connect test box ((VAG1598/42)) to Engine Control Module (ECM) (J623) wiring harness using adapter cable ((VAG1598/39-1)) , connecting test box for wiring test.

- Disconnect 2-pin connector - 1 - from Engine Coolant Temperature (ECT) Sensor (G62).





- Check wires between test box and 2-pin connector for open circuit according to wiring diagram.





Terminal 1+socket 52

Terminal 2+socket 53

Wire resistance: max. 1.5ohms

- Also check wires for short circuit to each other, to vehicle Ground (GND) and to B+.

Specified value: infinite ohms

If no malfunctions are found in wires:

- Measure resistance between terminals on sensor.

See diagram for specified value





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.

Read-out examples:

• 30 °C corresponds to a resistance of 1500 to 2000 ohms

• 80 °C corresponds to a resistance of 275 to 375ohms

If specified value is not obtained:

- Replace Engine Coolant Temperature (ECT) Sensor (G62).

CAUTION!
• The cooling system is under pressure.

• Danger of scalding when opening!

- Erase DTC memory of Engine Control Module (ECM) --> [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 09.

- Generate readiness code --> [ Readiness Code ] Monitors, Trips, Drive Cycles and Readiness Codes.

If no malfunctions are detected in the wires and the resistance values are OK:

- Replace Engine Control Module (ECM) (J623) --> [ Engine Control Modules, Replacing ] Engine Control Modules, Replacing.