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

Voltage Supply, Checking

Special tools, testers and auxiliary items required

• Multimeter.

• Wiring diagram.

Test requirements

• The Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) (J248) fuses 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 sequence

- Remove the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) Power Supply Relay (J317).

Checking voltage

- Using a Multimeter, check the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) Power Supply Relay (J317) socket 2/30 to Ground (GND).

Specified value: battery voltage.

If the specified value was not obtained:

- Check the wiring connections from the Battery to the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) Power Supply Relay (J317) socket 2/30 for an open circuit or a short circuit.

- Check the wiring connections for damage, corrosion, loose or broken terminals.

- If necessary, repair the faulty wiring connection.

If the specified value was obtained:

- Switch the ignition on.

- Using a Multimeter, check the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) Power Supply Relay (J317) socket 6/87 to Ground (GND).

Specified value: battery voltage.

If the specified value was obtained:

Checking wiring

If the manufacturers test box is being used, perform the following step.

- Install the test box. Refer to => [ 68 Pin Test Box Adapter, Installing ] 68 Pin Test Box Adapter, Installing.

If the manufacturers test box is not being used, perform the following step.

- Remove the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) (J248). Refer to => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.

- Using a Multimeter, check the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) Power Supply Relay (J317) socket 9/85 to the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) (J248) electrical harness connector T80 terminal 33 for resistance.





Specified value: 2.0 ohms Max.

If the specification was not obtained:

- Check the wiring for a short circuit to each other, Battery (+), and Ground (GND).

- Check the electrical harness connector for damage, corrosion, loose or broken terminals.

- If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring:

Checking activation

- Switch the ignition on.

- Using a Multimeter, check the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) Power Supply Relay (J317) socket 6/87 to the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) (J248) electrical harness connector T80 terminal 33 for voltage.





- Switch the ignition off.

Specified value: 0.5 V Max.

If the specified value was obtained:

- Replace the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) Power Supply Relay (J317).

If the specified value was not obtained:

- Check the wiring connection for an open circuit, short circuit to Battery (+) or Ground (GND).

- Check the wiring connection for damage, corrosion, loose or broken terminals.

- If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring and voltage supply was not OK:

- Replace the Diesel Direct Fuel Injection (DFI) Engine Control Module (ECM) (J248). Refer to => [ Engine Control Module, Replacing ] Engine Control Module, Replacing.

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 ] Readiness Code.

End of diagnosis