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

Component locations, refer to "Component Locations, Overview". Locations
Test requirement
- Engine cold

Test sequence
- Connect VAS 5051 vehicle diagnostic, testing and information system or V.A.G 1551 scan tool and select "Address word" 01 for control module for engine electronics.

When indicated on display

Rapid data transfer HELP
Select function XX

- Press buttons "08" for the function "read Measuring Value Block" and press Q button to confirm input.

When indicated on display

Read Measuring Value Block Q
Input Display Group Number

- Press buttons "004" for "Display group number 04" and confirm with the Q - button.

Indicated on display

Read Measuring Value Block 4 ->
1 2 3 4

- Check display in display field 3.

Display Group 4:

If no realistic display occurs in display field 3:

NOTE: Do not confuse the coolant temperature sensor which transmits its signal to the engine control module with the coolant temperature sensor, which sends its signal to the A/C.

- Disconnect connector from coolant temperature sensor.

Coolant temperature sensor with square connector





- Connect multimeter between sensor terminals 1 and 3 for a resistance measurement.

Coolant temperature sensor with oval connector





- Connect multimeter between sensor terminals 3 and 4 for a resistance measurement.

All models
Range A shows the resistance values for the temperature range of 0 - 50 °C range B shows the value for the temperature range of 50 - 100 °C.





Examples:
- 30 °C corresponds to a resistance of 1500 - 2000 ohm
- 80 °C corresponds to a resistance of 275 - 375 ohm

If the specified value is met:
- Connect test box VAG 1598/31 at wiring harness to engine control module, the engine control module is not to be connected.

Coolant temperature sensor with square connector





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

Harness connector Terminal Text box V.A.G 15981 socket
1(Signal) 108
3 93

Coolant temperature sensor with oval connector





- Check the following wire connections for open circuit and short circuit between Ground and B+:

Harness connector terminal text box V.A.G 1598/1 socket
3 108
4(Signal) 93

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

If no malfunctions are found in wires:
- Replace engine control module.