Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Checking wiring
- Connect test box to control module wiring harness. Refer to 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 Ω
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 Ω
Vehicles with 154-pin control module
- Connect adapter cable (V.A.G 1598/39-1) to test box (V.A.G 1598/42).
- 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 Ω
Continue for all vehicles
- Check wires for short circuit to each other, to vehicle Ground (GND) and to B+.
Specified value: ∞ Ω
If no malfunctions are found 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.
Continue for all vehicles
See diagram for specified value
Range A displays resistance values for the temperature range of 0 to 50 ° C, range B displays resistance values for the temperature range of 50 to 100 ° C.
Read-out examples:
- 30 ° C corresponds to a resistance of 1500 to 2000 Ω
- 80 ° C corresponds to a resistance of 275 to 375 Ω
If specified value is not obtained:
- Replace Engine Coolant Temperature (ECT) Sensor -G62- with Engine Coolant Temperature (ECT) Sensor -G2-:
- Vehicles with engine code ALH, Overview of component locations. Refer to item 10 in Component Locations, overview (vehicles with engine code ALH)
- Vehicles with engine code BEW, Overview of component locations. Refer to item 8 in Component Locations, overview (vehicles with engine code BEW) .
- Erase DTC memory of control module for Diesel-Direct fuel injection system. Refer to Diagnostic mode 4: Reset/erase diagnostic data .
- Generate readiness code.
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-. Refer to Control module for Diesel-Direct Fuel Injection System, replacing .
- Generate readiness code.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.