With Generic Scan Tool

Engine Coolant Temperature (ECT) Sensor, Checking

Recommended special tools and equipment
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram

Test requirements







- The respective fuses of Motronic Engine Control Module (ECM) - J220- must be OK.
- Parking brake must be engaged or else daylight driving lights will be switched on.
- Engine must be cold.

Function test
- Connect diagnostic tester. Diagnostic Tester, Connecting
- Switch ignition on.
- Under address word 33, select "Diagnostic mode 1: Checking measuring values."
- Select the measuring value "PID 05: Coolant temperature".
- Check specified value of coolant temperature:







If specified value is obtained:
- Start engine and let run at idle. The temperature should climb uniformly

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.

If no realistic indication follows:
- Disconnect connector at coolant temperature sensor.

Coolant temperature sensor with square connector:







- Connect multimeter between terminal 1 and 3 of sensor for resistance measurement.

Coolant temperature sensor with oval connector:







- Connect multimeter between terminal 3 and 4 of sensor for resistance measurement.

All:
Range A displays resistance values for the temperature range of 0...50 degree C, range B displays resistance values for the temperature range of 50...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 coolant temperature sensor.

If specified value is obtained:
- Connect test box to control module wiring harness, connect test box for wiring test. Test Box, Connecting For Wiring Test

Coolant temperature sensor with square connector:







- Check the following wire connections for open circuit and short circuit to Ground (GND) and B+:

Harness connector VAG1598/31 test box
Terminal Socket
1(signal) 93
3 108

Coolant temperature sensor with oval connector:







- Check the following wire connections for open circuit and short circuit to Ground (GND) and B+:

Harness connector VAG1598/31 test box
Terminal Socket
3 108
4(signal) 93

All:
- Check both wires to each other for short circuit.
- Repair open circuit or short circuit if necessary.

If no wiring faults are found:
- Replace Engine Control Module (ECM).