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

Engine Coolant Temperature (ECT) Sensor, Checking


NOTE: If a DTC relating to the Engine Coolant Temperature (ECT) sensor -G62- is stored in DTC memory, the Engine Control Module (ECM) uses a replacement value when starting the engine (starting temperature replacement value). After this, the temperature rises according to a mapping specification stored in the Engine Control Module (ECM). For a warm engine, a fixed replacement value is indicated after a certain period of time. This fixed replacement value is also dependent on the intake air temperature.


Special tools and equipment
- VAG1551 scan tool (or VAG1552 mobile scan tool) with VAG1551/3B cable
- VAG1598/31 test box
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram

Test requirement
- Engine must be cold.

Test sequence


NOTE: When servicing terminals 3 and 4 in the harness connector for the coolant temperature sensor, use only gold-plated terminals.


- Connect VAG1551 scan tool (VAG1552). Then switch ignition on and select the Engine Control Module (ECM) using address word 01.

Connecting scan tool and selecting ECM. Refer to " Scan Tool Testing/Scan Tool Connecting and Initial Checks " 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. Press -Q- button to confirm input.

Indicated on display:


Read measuring value block
Enter display group number XXX


- Press 0, 0 and 4 for the function "display group number 4", and then press Q to exit from input mode.

Indicated on display: (1 to 4 = display fields)


Read measuring value block 4 ->
1 2 3 4


- Read coolant temperature value in display field 3.

Display Group 4:

- Start engine and let run at idle. The temperature should climb uniformly

If specified value is not obtained:
- Press the -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.
- Replace Engine Coolant Temperature (ECT) sensor -G62- with Engine Coolant Temperature (ECT) sensor -G2-.


NOTE: The temperature rises in increments of 1.0 °C.


- Check DTC memory, repair any malfunctions and then erase DTC memory.

Evaluation display group 4, display field 3 - coolant temperature







Continuation of test if indication is approx. -40.0 °C:







- Disconnect 4-pin connector from Engine Coolant Temperature (ECT) sensor -G62- with Engine Coolant Temperature (ECT) sensor -G2- (arrow)







- Bridge terminals 3 + 4 of connector using adapter cables from VAG1594 connector test kit, and observe what is indicated on display.

If indication jumps to approx. 140.0 °C:
- Press the -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.
- Replace Engine Coolant Temperature (ECT) sensor -G62- with Engine Coolant Temperature (ECT) sensor -G2-.
- Check DTC memory, repair any malfunctions and then erase DTC memory.

If indication remains approx. -40.0 °C:
- Press the -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.
- Check wires according to wiring diagram.

Continuation of test if indication is approx. -40 °C:







- Disconnect 4-pin connector from Engine Coolant Temperature (ECT) sensor -G62- with Engine Coolant Temperature (ECT) sensor -G2- (arrow)

If indication jumps to approx. -40.0 °C:
- Press the -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.
- Replace Engine Coolant Temperature (ECT) sensor -G62- with Engine Coolant Temperature (ECT) sensor -G2-.
- Check DTC memory, repair any malfunctions and then erase DTC memory.

If indication remains at approx. 140.0 °C:
- Press the -> button.
- Press buttons -0- and -6- to select ".End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.
- Check wires according to wiring diagram.

Checking wiring







- Connect VAG1598/31 test box to control module wiring harness. Engine Control Module (ECM) is not connected.







- Disconnect 4-pin connector from Engine Coolant Temperature (ECT) sensor -G62- with Engine Coolant Temperature (ECT) sensor -G2- (arrow)







- Check wires between test box and 4-pin connector for open circuits according to wiring diagram.

Terminal 3 + socket 93
Terminal 4 + socket 108

Wire resistance: max: 1.5 Ohms

- Use wiring diagram to check wire between test box and 4-pin connector terminal 3 for short circuit to wire of terminal 4 and to vehicle Ground (GND).

Terminal 4 + socket 93
Terminal 3 + vehicle Ground (GND)

Specification: Infinity Ohms

- Also check both wires for short circuit to B+. Specification: Infinity Ohms

If no malfunctions are found in wire:







- Measure resistance at Engine Coolant Temperature (ECT) sensor -G62-, terminals C (signal) and D (Ground -GND-).







Range A shows the resistance values for the temperature range from 0-50 °C, and range B shows the values for the temperature range from 50-100 °C.

Read-out examples:
- 30 °C corresponds to a resistance of 1500 to 2000 Ohms
- 80 °C corresponds to a resistance of 275 to 375 Ohms

specified value is not obtained:
- Replace Engine Coolant Temperature (ECT) sensor -G62- with Engine Coolant Temperature (ECT) sensor -G2-.
- Check DTC memory, repair any malfunctions and then erase DTC memory.

If no malfunctions are found in the wires and the resistance values are OK:
- Replace Engine Control Module (ECM).

After successful repair:
- Read readiness code. Refer to Monitors, Trip and/or Drive Cycle (Readiness Codes)/Reading Readiness Code. Testing and Inspection
If DTC memory was erased or the Engine Control Module (ECM) was disconnected from the continuous B+ supply, the readiness code must be re-generated. Refer to Monitors, Trip and/or Drive Cycle (Readiness Codes)/Generating Readiness Code. Testing and Inspection