Coolant Temperature Sensor/Switch (For Computer): Testing and Inspection
ENGINE COOLANT TEMPERATURE SENSOR, CHECKING
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
NOTE: If the engine is warmed to operating temperature with the vehicle stationary, and the time taken to reach operating temperature is too long, it can lead to DTC P0116 or P0125 being stored in DTC memory In this case, erase DTC memory and bring engine to operating temperature during a test drive.
Test conditions
- Engine cold
Test sequence
- Connect VAG 1551/1552 scan tool and select "Engine Electronics" address word 01. When doing this the ignition must be switched on. Refer to"On-Board Diagnostics II With VAG 1551". Testing and Inspection
Indicated on display
Rapid data transfer HELP
Select function XX
- Press buttons -0- and -8- to select "Read Measuring Value Block" function 08 and press -Q- button to confirm input.
Indicated on display
Read Measuring Value Block HELP
Input display group number XXX
- Press buttons -0-, -0- and -1- for display group 001 and press -Q- button to confirm input.
Indicated on display (1-4 = Display fields)
Read Measuring Value Block 1 ->
1 2 3 4
- Check the specification for engine coolant temperature sensor (display field 2).
- 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.
- 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
Checking wiring
- Connect VAG 1598/18 test box to ECM wiring harness.
- Disconnect 4-pin connector -1- from ECT sensor -G62- -2-.
- Check wiring between test box and 4-pin connector for open circuit according to wiring diagram.
- Terminal 1 and test box socket 33
- Terminal 3 and test box socket 14
Resistance: maximum 1.5 Ohms
- Check wiring between test box and 4-pin connector terminal 3 for short circuit to terminal 1 or to Ground (GND), according to wiring diagram.
- Terminal 3 and test box socket 33
- Terminal 3 and vehicle Ground (GND)
Specification: Infinity Ohms
- Additionally, check both wires for short circuit to battery Positive (B+).
Specification: Infinity Ohms
If no malfunction in wiring is detected:
- Perform resistance measurement at ECT sensor -G62- terminals 1 and 3, resistance values.
Resistance Graph
The diagram applies to 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 shows 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, repair must be verified via appropriate display group See, Readiness code, creating. Refer to "On-Board Diagnostics II With VAG 1551". Testing and Inspection