Motronic Engine Control Module Power Supply Relay J271, Checking

Motronic Engine Control Module Power Supply Relay J271, Checking

Special tools, testers and auxiliary items required
- Multimeter
- wiring diagrams

Test requirements
- The Motronic Engine Control Module (ECM) J623 fuses OK.
- Fuse SB26 OK.
- The Ground (GND) connections at the engine and transmission OK.
- The battery voltage at least 12.5 V.
- The generator OK.

Test procedure
- Perform a preliminary check to verify the customers complaint. Preliminary Check

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

Motronic Engine Control Measure to
Module (ECM) Power Supply
Relay J271 socket
3/86 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 3/86 to the Battery 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:
- Using a Multimeter, check the following wiring connection for voltage.

Motronic Engine Control Measure to
Module (ECM) Power Supply
Relay J271 socket
1/30 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 to the Battery 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)
If the manufacturers test box is being used. Perform the following step.
- Install the test box.

If the manufacturers test box is not being used. Perform the following step.
- Remove the Motronic Engine Control Module (ECM) J623.
- Using a Multimeter, check the following wiring connection for resistance.

Motronic Engine Control Module Motronic Engine Control Module
(ECM) Power Supply Relay J271 (ECM) J623 electrical harness
socket connector T94 or test box socket
4/85 69

Specified value: 1.5 Ohms.

If the specified value was not obtained:
- Check the Motronic Engine Control Module (ECM) Power Supply Relay J271 socket 4/85 to the Motronic Engine Control Module (ECM) J623 electrical harness connector T94 terminal 69 for an open circuit or a short to Battery (+).
- 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 Motronic 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