Engine Control Module Power Supply Relay, Checking

Engine Control Module Power Supply Relay, Checking

Special tools, testers and auxiliary items required
- Multimeter.
- Wiring diagram.

Test requirements
- Fuse Strip S88 OK.
- Battery voltage at least 12.5 volts.
- All electrical consumers such as, lights and rear window defroster, switched off.
- Vehicles with automatic transmission, selector lever in position "P" or "N".
- A/C switched off.
- Ground (GND) connections between engine/transmission/chassis OK.
- Ignition switched off.

Test procedure
- Perform a preliminary check to verify the customers complaint. General Diagnosis

Start diagnosis
- Using a Multimeter , check the following wiring connections for voltage.

Motronic Engine Control Measure to
Module (ECM) Power Supply
Relay J271 socket
1/30 Engine Ground (GND)
3/T Engine Ground (GND)

Specified value: 12.5 V

If the specified value was not obtained:
- Check the Motronic Engine Control Module (ECM) Power Supply Relay J271 socket 1/30 and 3/T to the Battery A (+) terminal for an open circuit or short to Ground (GND).
- Check the electrical harness connectors for damage, corrosion, loose or broken terminals.
- If necessary, repair the wiring connection.

If no malfunctions are found in the wiring:

Checking Ground (GND)
- Using a Multimeter , check the Motronic Engine Control Module (ECM) Power Supply Relay J271 socket 4/86 to the Engine Control Module (ECM) J623 electrical harness connector terminal T94/69 for resistance.

Specified value: 1.5 Ohms.

If the specified value was not obtained:
- Check the Motronic Engine Control Module (ECM) Power Supply Relay J271 socket 4/86 to the Engine Control Module (ECM) J623 electrical harness connector terminal T94/69 for an open circuit or a short to Battery (+) or to Ground (GND).
- Check the electrical harness connector for damage, corrosion, loose or broken terminals.
- If necessary, repair the wiring connection.

If no malfunctions are found in the wiring and the voltage supply was OK:
- Replace the Motronic Engine Control Module (ECM) Power Supply Relay J271.
- Perform a road test to verify repair.

If the fault does not return:

Repair complete, Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
- End diagnosis.

If the fault does return and no malfunction is detected in the wiring and the voltage supply was OK:
- Replace the Engine Control Module (ECM) J623.
- Assembly is performed in the reverse of the removal.

Final procedures
After repair work, the following work steps must be performed in the mentioned sequence:
1. Check the DTC memory. Diagnostic Mode 03 - Read DTC Memory
2. If necessary, erase the DTC memory. Diagnostic Mode 04 - Erase DTC Memory
3. If the DTC memory was erased, generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

End of diagnosis.