Main Relay (Computer/Fuel System): Testing and Inspection

Motronic Engine Control Module Power Supply Relay, Checking

Special tools, testers and auxiliary items required

• Multimeter

• wiring diagrams

Test requirements

• The fuse for the engine electronics OK.

• The Ground (GND) connections at the engine and transmission OK.

• The battery voltage at least 12.5 V.

• The generator OK.

• The ignition is switched off.

Test sequence

- Switch the ignition on.

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





Specified value: approx. battery voltage.

- Switch the ignition off.

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





- Switch ignition on.

Specified value: 12.5. battery voltage.

- Switch the ignition off.

If the specified values are not obtained:

- Using the Multimeter, check previously checked wiring connections for continuity.

Specified value: Wire resistance max 1.5 ohms.

- If necessary, repair the wiring connection.

If no malfunctions are found in the wiring:

- Replace the Motronic Engine Control Module (ECM) Power Supply Relay (J271).

Final procedures

After the repair work, the following work steps must be performed in the following sequence:

1. Check the DTC memory. Refer to => [ Diagnostic Mode 03 - Read DTC Memory ] Diagnostic Mode 03 - Read DTC Memory.

2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Mode 04 - Erase DTC Memory.

3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code, Setting ] Readiness Code, Setting.

End of Diagnosis.