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

Voltage Supply Relay, Checking

Observe all safety precautions: => [ Safety Precautions ] Generic Scan Tool

View clean working conditions: => [ Clean Working Conditions ] Clean Working Conditions

Prior to repair work, perform a preliminary check to verify the condition. Refer to => [ Preliminary Check ] Preliminary Check.

Use only gold-plated terminals when servicing any component with gold-plated electrical harness connector terminals.

For wiring diagrams, component locations, and connector views, Refer to the applicable wiring diagram.

Special tools, testers and auxiliary items required

• Multimeter

• Wiring diagram

Test requirements

• The engine control module fuses OK

• Battery voltage at least 12.5 volts

• All electrical consumers switched off

• Vehicles with automatic transmission, shift selector lever in park or neutral

• A/C switched off

• Ground connections between engine/transmission/chassis OK

• Ignition switched off

Test procedure

- Remove the engine control module power supply relay.

Checking the supply voltage

- Using a multimeter, measure the voltage of the engine control module power supply relay circuit (socket 1/30).

Specified value: battery voltage.

If the specified value was not obtained:

- Check the power supply circuit to the engine control module power supply relay for an open circuit or a short circuit.

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

- Repair as necessary.

- Switch the ignition on.

- Using a multimeter, measure the voltage of the engine control module power supply relay ignition circuit (socket 3/86).

Specified value: battery voltage.

If the specified value was not obtained:

- Check the ignition circuit to the engine control module power supply relay for an open circuit or a short circuit.

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

Checking wiring

- Remove the engine control module. Refer to the service manual for removal and installation procedures.

- Using a multimeter, measure the resistance of the circuit between the power supply relay and the engine control module. Refer to the applicable wiring diagram.

Specified value: 1.5 ohms Max.

If the specification was not obtained:

- Check the wires for a short circuit to each other, a short to battery voltage, and a short to ground.

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

- Repair as necessary.

If no malfunction is found in the wiring and voltage supply was OK:

- Replace the engine control module power supply relay.

Final procedures

After 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 Modes 01 - 09.

2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 09.

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