Engine Temperature Sensor: Testing and Inspection
Engine Coolant Temperature (ECT) Sensor, Checking
Recommended special tools and equipment
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram
Test requirement
- Engine must be cold.
- The respective fuses of Diesel-Direct fuel injection system must be OK:
- Battery voltage must be at least 11.5 Volts.
Function test
- Connect diagnostic tester. Diagnostic Tester, Connecting
- Switch ignition on.
- Under address word 33, select "Diagnostic mode 1: Check measured values."
- Select the measuring value "PID 05: Coolant temperature".
- Check specified value of coolant temperature:
PID Diagnostic Text Specified Value:
05: Coolant temperature approx. coolant temperature
If specified value is not obtained:
- End diagnosis and switch ignition off.
- Check wires according to wiring diagram.
If specified value is obtained:
- Start engine and let run at idle.
- Check specified value of coolant temperature at idle:
NOTE: The temperature increases in increments of 1.0° C.
- If the engine indicates problems in certain temperature ranges and if the temperature does not climb uniformly, the temperature signal is intermittent and the sensor must be replaced.
Checking wiring
- Connect test box to control module wiring harness, connect test box for wiring test. Test Box, Connecting For Wiring Test
Vehicles with 80-pin control module
- Check wires between test box and 4-pin connector for open circuit according to wiring diagram.
Terminal 1 + socket 70
Terminal 3 + socket 54
Wire resistance: max. 1.5 Ohm
Vehicles with 121-pin control module
- Check wires between test box and 4-pin connector for open circuit according to wiring diagram.
Terminal 3 + socket 112
Terminal 4 + socket 104
Wire resistance: max. 1.5 Ohm
Vehicles with 154-pin control module
- Check wires between test box and 4-pin connector for open circuit according to wiring diagram.
Terminal 3 + socket 52
Terminal 4 + socket 53
Wire resistance: max. 1.5 Ohm
Continuation for all vehicles
- Also check wires for short circuit to each other, to vehicle Ground (GND) and to B+.
Specified value: Infinite Ohm
If no malfunctions are detected in wires:
Vehicles with 80-pin control module
- Disconnect 4-pin connector from Engine Coolant Temperature (ECT) Sensor -G62- with Engine Coolant Temperature (ECT) Sensor -G2- (arrow).
- Perform a resistance measurement at Engine Coolant Temperature (ECT) Sensor -G62- terminal 1 (Ground -GND-) and 3 (signal).
Vehicles with 121-pin control module
- Disconnect connector at coolant temperature sensor.
- Measure resistance between terminals 3 + 4 on sensor.
Vehicles with 154-pin control module
- Disconnect connector at coolant temperature sensor.
- Measure resistance between terminals 3 + 4 on sensor.
Continuation for all vehicles
See diagram for specified value.
Range A displays resistance values for the temperature range of 0...50 degree C, range B displays resistance values for the temperature range of 50...100 degree C.
Read-out examples:
Continuation for all vehicles
30° C corresponds to a resistance of 1500 to 2000 Ohm
80° C corresponds to a resistance of 275 to 375 Ohm
If specified value is not obtained:
- Replace Engine Coolant Temperature (ECT) Sensor -G62- with Engine Coolant Temperature (ECT) Sensor -G2-.
- Erase DTC memory of control module for Diesel- Direct fuel injection system, Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 4: Reset/Erase Diagnostic Data
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
If no malfunctions are detected in the wires and the resistance values are OK:
- Replace Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) -J248-
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes