Main Relay Test

Symptom Of Fault.
The engine fails to start





Diagnostic Procedure.
1. Check the operation of the main relay

- Connect an ISAT scan tool.
- Ignition switch in ON position.
- Select "ACTIVATE".
- Select "MAIN RELAY". The main relay is activated for 10 seconds at a frequency of 1 Hz. If a longer activation time is required, the command will have to be repeated.
- Listen for the sound of the main relay and idle air control valve working. They should both click at a frequency of 1 Hz (once a second).

Does only the main relay click?

YES: Continue with point 2.
NO: Neither the main relay nor the idle air control valve clicks. Continue with point 5.





2. Check fuse 16B

Is the fuse OK?

YES: Continue with point 3.
NO: Change the fuse and continue with point 3.

3. Forcibly supply the main relay with power

- Connect a jumper lead between fuses 4 and 16B.

Does the idle air control valve click?

YES: Continue with point 4.
NO Repair or replace the lead between fuse 16 and crimped connection J67.





4. Check the main relay

- Remove the main relay.
- Connect a jumper lead between pins 30 and 87 on the relay holder.

The idle air control valve should click.

Does the valve click?

YES: Change the main relay.
NO: Check the lead between pin 87 and fuse 16B and the lead between pin 30 and battery positive (B+). Repair or replace the leads if necessary.

5. Check the main relay

- Remove the main relay.
- Connect the test lamp to pins 85 and 86 of the relay holder.
- Ignition switch in ON position.
- Select "ACTIVATE".
- Select "MAIN RELAY".

The test lamp should flash.

Does the test lamp flash?

YES: Change the main relay.
NO: Proceed to point 6.





6. Check the main relay's power supply

- Connect the test lamp to pin 86 of the relay holder and a good grounding point.
The test lamp should light up.

Is the test lamp on?

YES: Continue with point 7.
NO: Check the lead between pin 86 and battery positive (B+). Repair or replace it if necessary.

7. Check the main relay's connection to ground

- Check and if necessary repair or replace the lead between pin 85 of the relay holder and pin 31 of the control module.

Is the lead OK?

YES: Continue at "Before Replacing a Control Module". Component Tests and General Diagnostics
NO: Rectify the fault.