Engine Temperature Sensor: Testing and Inspection

Engine Coolant Temperature (ECT) Sensor, Checking

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

Recommended special tools and equipment
- V.A.G 1526 multimeter or V.A.G 1715 multimeter
- V.A.G 1594 connector test kit
- Wiring diagram

Test requirements







- 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. Refer to Diagnostic Tester, Connecting. Diagnostic Tester, Connecting
- 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.
- Check wires to control module.

If specified value is obtained:
- Start engine and let run at idle.
- Check specified value of coolant temperature at idle:







NOTE:
- The temperature increases 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 and the sensor should be replaced.

- End diagnosis and switch ignition off.

Check wires to control module
- Connect test box (1598/42) to Engine Control Module (ECM) -J623-wiring harness using adapter cable (V.A.G 1598/39-1). Refer to Connecting test box for wiring test. Test Box, Connecting 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. 1.5 ohm

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

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 degree C, range B displays resistance values for the temperature range of 50 to 100 degree C.

Read-out examples:
- 30 degree C corresponds to a resistance of 1500 to 2000 ohm
- 80 degree C corresponds to a resistance of 275 to 375 ohm

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

WARNING:
- The cooling system is under pressure.
- Danger of scalding when opening.

- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Refer to Diagnostic Mode 4: Reset/Erase Diagnostic Data.
- Generate readiness code. Refer to Readiness Code, Generating. 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-.