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

Engine Coolant Temperature (ECT) Sensor, Checking

Special tools and equipment
- Scan tool VAG 1551 or vehicle system tester VAG 1552 with cable VAG 1551/3
- Test box VAG 1598/31
- Hand multimeter VAG 1526 or multimeter VAG 1715
- Adapter set VAG 1594
- Wiring diagram

Test conditions
- Engine must be cold.

Test sequence
- Connect the scan tool VAG 1551 (VAG 1552). Then switch ignition on and select engine control module with the "Address word" 01.
(Connecting scan tool and selecting engine control module). Refer to "VAG 1551 Scan Tool" [1][2][3][4][5]Connecting VAG 1551 Scan Tool

Indicated on display:


Rapid data transfer HELP
Select function XX


- Press keys 0 and 8 for the function "Read measured value block" and confirm entry with Q key.

Indicated on display:


Read measured value block HELP
Input display group number XX


- Press keys 0, 0 and 4 for "Display group number 4" and confirm entry with Q key.

Indicated on display: (1-4 = Display zones)


Read measured value block 4 ->
1 2 3 4


- Read off coolant temperature value in display zone 3.
Specification: approx. coolant temperature

If the specification is not obtained:
- Perform check according to following table:







If the specification is obtained:
- Start engine and run at idling speed.
The temperature value must increase uniformly


NOTE:
- Temperature increases in steps of 1.0 °C.
- If irregular engine running occurs in certain temperature ranges and the temperature figure does not increase without interruption, the temperature signal is temporarily interrupted and the sender must be replaced.


- Press -> key.
- Press keys 0 and 6 for the function "End output" and confirm entry with the Q key.

Continuation of check when display approx. -48 °C:







- Pull the 4-pin connector off Engine Coolant Temperature (ECT) sensor (G62) with coolant temperature gauge sender (G2) (arrow).







- Bridge connector contacts 3 + 4 using adapter cables from VAG 1594 and observe display.


If display jumps to approx. 143 °C:
- Press -> key.
- Press keys 0 and 6 for the "End data transfer" function and confirm input with the Q key.
- Switch off ignition.
- Replace Engine Coolant Temperature (ECT) sensor (G62).


If display remains at approx. -48 °C
- Press -> key.
- Press keys 0 and 6 for the "End data transfer" function and confirm input with the Q key.
- Switch off ignition.
- Check wiring using wiring diagram

Continuation of check when display approx. 143 °C:







- Pull the 4 pin connector off Engine Coolant Temperature (ECT) sensor (G62) with coolant temperature gauge sender (G2) -arrow-.

If display jumps to approx. -48 °C:
- Press -> key.
- Press keys 0 and 6 for the "End data transfer" function and confirm input with the Q key.
- Switch off ignition.
- Replace Engine Coolant Temperature (ECT) sensor (G62).

If display remains at approx. 143 °C:
- Press -> key.
- Press keys 0 and 6 for the "End data transfer" function and confirm input with the Q key.
- Switch off ignition.
- Check wiring using wiring diagram

Checking wiring







- Connect test box VAG 1598/31 to control module wiring harness. The engine control module remains disconnected.







- Pull 4-pin connector off Engine Coolant Temperature (ECT) sensor (G62) with coolant temperature gauge sender (G2) (arrow).







- Check wiring between test box and 4-pin connector for open circuit using wiring diagram.
Contact 3 + socket 93
Contact 4 + socket 108
Wire resistance: Max. 1.5 ohms
- Check wiring between test box and 4-pin connector contact 3 for short circuit to wire contact 4 and to vehicle Ground using wiring diagram.
Contact 3 + socket 108
Contact 3 + vehicle Ground
Specification: Infinity ohms
- Additionally check both wires for short to battery positive.

If no fault in wire is detected:







- Perform resistance measurement on Engine Coolant Temperature (ECT) sensor (G62) contact C (signal) and D (Ground).







Scale A shows resistance values for temperature range 0 - 50 °C and scale B the values for temperature range 50 - 100 °C.

Examples:
- 30 °C is in range A and corresponds to a resistance of 1.5 - 2.0 kOhms
- 80 °C is in range B and corresponds to a resistance of 275 - 375 ohms

If the specification is not obtained:
- Replace Engine Coolant Temperature (ECT) sensor (G62).

If there is no fault in the wiring and the resistance measurement values are OK.:
- Replace engine electronics control module.