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

Engine Coolant Temperature (ECT) Sensor -G62-, Checking

Special tools and equipment
- VAG 1551 Scan Tool or VAG 1552 with cable
- VAG 1551/3
- Test box VAG 1598/22
- Hand multimeter VAG 1526 or multimeter VAG 1715
- Adapter set VAG 1594
- Wiring diagram

NOTE: The engine control module will use the intake air temperature as a replacement value for an engine start (start temperature replacement value) as soon as there is a malfunction stored in the DTC memory, which affects the engine coolant temperature (ECT) sensor -G62-. The temperature then rises according to a model stored in the control module. When the engine has reached normal working temperature a fixed replacement value will be displayed after a certain period. This fixed value is also dependent upon the intake air temperature.

Test conditions
- Engine must be cold.

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

Indicated on display

Rapid data transfer HELP
Select function XX

- Press keys 0 and 8 for function "Read Measuring Value Block" and confirm entry with Q key.

Indicated on display

Read Measuring 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 to 4 Display zones)

Read Measuring Value Block 4 ->
1 2 3 4

If the specification is not obtained:
- Read off coolant temperature value in display zone 3.
Specification: approx. coolant temperature
- Perform check according to following table:

Display1) Cause
Approx. -46 degree C Open circuit or short to positive
Approx. 141 degree C Short to Ground
1) If a temperature is displayed which deviates greatly from the ambient temperature of the sensor, check sensor wiring for transfer resistances.

If the specification is obtained:
- Start engine and run at idle speed. Temperature value must increase uniformly.

NOTE:
- Temperature rises in steps of 1.5 degree 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 sensor must be replaced.

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

Continuation of check when display approx. -46 degree C:







- Pull 4 pin connector -1- off coolant temperature sensor -G62- -2-.
- Bridge connector contacts 1+3 using auxiliary cables from VAG 1594 and observe display.

If display jumps to approx. 141 degrees C:
- Press -> key.
- Press keys 0 and 6 for "End data transfer" function and confirm input with Q key.
- Switch ignition off.
- Replace engine coolant temperature (ECT) sensor -G62-.

If display jumps to approx. -46 degree C:
- Press -> key.
- Press keys 0 and 6 for "End data transfer" function and confirm input with Q key.
- Switch ignition off.
- Check wiring using wiring diagram.

Continuation of check when display approx. 141 degree C:







- Pull 4 pin connector -1- off engine coolant temperature (ECT) sensor -G62- -2-.

If display jumps to approx. -46 degree C:
- Press -> key.
- Press keys 0 and 6 for "End data transfer" function and confirm input with Q key.
- Switch ignition off.
- Replace engine coolant temperature (ECT) sensor -G62-.

If display remains at approx. 141 degree C:
- Press -> key.
- Press keys 0 and 6 for "End data transfer" function and confirm input with Q key.
- Switch ignition off.
- Check wiring using wiring diagram

Checking wiring







- Connect test box VAG 1598/22 to control module wiring harness.







- Check wires between test box and 4-pin connector for open circuit according to wiring diagram.
Contact 4 + vehicle ground
Contact 3 + socket 53
Wire resistance: max. 1.5 Ohm
- Check wires for short circuit to each other as well as to vehicle Ground.
- Check both wires for short to battery positive.

If no malfunction 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 to 50 degree C and scale B the values for temperature range 50 to 100 degree C.

Examples:
- 30 degree C is in range A and corresponds to a resistance of 1.5 to 2.0 kOhm
- 80 degree C is in range B and corresponds to a resistance of 275 to 375 Ohm

If the specification is not obtained:
- Replace engine coolant temperature (ECT) sensor -G62-.

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