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

Special tools, testers and auxiliary items:
- VAG 1551/1552 scan tool with VAG 1551/3 adapter cable.
- VAG 1598/18 test box.
- Multimeter (Fluke 83 or equivalent).
- Connector test kit VW 1594.
- Wiring diagram.

Test conditions:
- Engine cold

Test sequence:
- Connect VAG 1551/1552 scan tool and select "Engine Electronics" address word 01. Testing and Inspection When doing this ignition must be switched on.




Indicated on display
- Press buttons -0- and -8- to select "Read Measuring Value Block" function 08 and press -Q- button to confirm input.




Indicated on display
- Press buttons -0-, -0- and -1- to input display group 001 and press -Q- button to confirm input.




Indicated on display (1-4 = Display fields)
- Check the specification for coolant temperature sensor (display field 2).





Continuation
- Start engine and run at idle speed.
- The temperature value must increase uniformly.

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


WARNING:! The cooling system is pressurized when the engine is warm. When opening the expansion tank, wear gloves and other appropriate protection, cover the cap with a cloth, and open carefully to relieve system pressure slowly.


- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06 and press -Q- button to confirm input.
- Switch ignition off.


NOTES:
- Display on VAG 1551 scan tool jumps by 1.5°C increments.
- If irregular engine running occurs in certain temperature ranges and the temperature value does not increase without interruption, the temperature signal is temporarily interrupted and the sensor must be replaced.

Evaluating display group 001




Check wiring





- Connect VAG 1598/18 test box to ECM wiring harness (arrow).





- Disconnect 2-pin connector from Engine Coolant Temperature (ECT) sensor -G62-.





- Check wiring between test box and 2-pin connector for open circuit according to wiring diagram.
- Terminal 1 and test box socket 14.
- Terminal 2 and test box socket 33.
Resistance: max. 1.5 ohms.
- Check wire between ECM connector and 2-pin connector terminal 2 for short circuit to wire terminal 1 and to vehicle Ground (GND), according to wiring diagram.
Terminal 2 and test box socket 14
Specification: infinite ohms.
- Additionally, check both wires for short circuit to battery positive (B+).
Specification: infinite ohms.

If no malfunction in wire is detected:
- Perform resistance measurement at ECT sensor -G62- terminals 1 and 2, resistance values See Fig. 1.





Fig. 1 Resistance graph

The diagram is valid for Engine Coolant Temperature (ECT) sensor -G62- and Intake Air Temperature (IAT) sensor -G72-.
Scale A shows resistance values for temperature range 0°-50°C (32°-122°F) and scale B the values for temperature range 50°-100°C (122°-212°F).
Examples:
- 30°C (86°F) corresponds to a resistance from 1500-2000 ohms.
- 80°C (176°F) corresponds to a resistance from 275-375 ohms.

If the specification is not attained:
- Replace ECT sensor -G62-.
- Read the readiness code. If DTC memory has been erased, verify repair via appropriate display group See Readiness code, creating. Testing and Inspection