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

Engine Coolant Temperature Sensor, Checking

Special tools and equipment
- VAG 1551/1552 Scan Tool using VAG 1551/3 adapter cable
- VAG 1598/18 Test Box
- Fluke 83 multimeter (or equivalent)
- VW 1594 Adapter kit
- Wiring diagram


NOTE: If an engine reaches operating temperature while stationary or takes too long to reach operating temperature due to unfavorable conditions, this can lead to DTC P0116 or P0125 being stored in DTC memory. If so, erase DTC memory and bring the engine to operating temperature during a test drive.


Test conditions
- Engine cold

Test sequence
- Connect VAG 1551 (VAG 1552) Scan Tool. Refer to Scan Tool Testing/VAG 1551 Scan Tool Testing and Inspection
- With ignition switched on but engine not running, press buttons -0- and -1- to select "Engine electronics" address word 01.

Display will appear as shown


Rapid data transfer HELP
Select function XX


- Press buttons -0- and -8- to select "Read measuring value block".
- Press -Q- button to enter selection.

Display will appear as shown


Read measuring value block HELP
Input display group number XXX


- Press buttons -0-, -0- and -1- to select "Display group number 1".
- Press -Q- button to enter selection.

Display will appear as shown (1 to 4 = Display fields)


Read measuring value block 1 ->
1 2 3 4


- Check specification for Engine Coolant Temperature sensor (Display field 2).

The temperature must match the specified values.


NOTE:
- The display on the scan tool jumps by 1.5 °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.


Evaluating display group 1







Continuation:

If the specification not obtained:
- Press -> key.
- Press buttons -0- and -6- to select "End output" and confirm entry with -Q- button.
- Switch ignition off.
- Remove insulation tray.
- Check vacuum line from intake manifold to cooling system vacuum valve.

Wiring, checking







- Connect VAG 1598/18 Test Box to ECM wiring harness.







- Disconnect 2-pin Engine Coolant Temperature sensor -G62-.







- Check wiring for open circuit between Test Box and 2-pin connector using wiring diagram, connect as follows:
terminal 1 + socket 14
terminal 2 + socket 33
- wire resistance: 1.5 Ohms maximum
- Using wiring diagram, check for short between control module connector and 2-pin connector terminal 2 and wire terminal 1 and GND
terminal 2 + socket 14
- specification: infinity Ohms
- Additionally check both wires for short to battery positive.
- specification: infinity Ohms

If wiring OK:
- Measure resistance at Engine Coolant Temperature sensor -G62- terminals 1 + 2.

If specification not obtained:
- Replace Engine Coolant Temperature sensor -G62-.
- Read-out Readiness code Refer to Monitors, Trip and/or Drive Cycle (Readiness Codes)/Readiness Code Checking. Testing and Inspection

If DTC memory has been erased:
- Create Readiness code Refer to Monitors, Trip and/or Drive Cycle (Readiness Codes)/Readiness Code Generating Testing and Inspection