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

Control Relay And Ignition Switch-IG Circuit:

Failure of the control relay could interrupt power supply to the fuel pump, injectors and ECU, resulting in start failure.

CAUTION: Use caution when connecting jumper wires to the relay. If the polarity is incorrectly connected, the relay will be damaged.


COMPONENT TEST
1. Supply 12 VDC to relay terminals 8 (-) and 6 (+). Using a voltmeter, check for voltage between terminals 2 (+) and 8 (-) and between terminals 1 (+) and 8 (-). Refer to Fig. 1.

Voltage
12 VDC


2. Supply 12 VDC to relay terminals 10 (-) and 7 (+). Using an ohmmeter, check for continuity between terminals 3 and 4.

Continuity
Should exist when voltage is supplied.
Should NOT exist when voltage is NOT supplied.


3. Supply 12 VDC to relay terminals 9 (-) and 3 (+). Using a voltmeter, check for voltage between terminals 3 (+) and 4 (-).

Voltage
12 VDC when terminal 9 is connected.
0 VDC when terminal 9 is NOT connected.

HARNESS TEST
1. Disconnect the negative battery cable and the ECU connector.
2. Reconnect the negative battery cable and turn the key to the ON position.
3. Using a volt meter, check the voltage between ECU harness terminal 6 and ground.

Voltage
System voltage.

4. Turn the key to the OFF position.
5. Disconnect the control relay connector.
6. Using an volt meter, check the voltage between relay harness terminal 6 and ground.

Voltage
System voltage.

7. Using a ohm meter, check for continuity between relay harness terminal 8 and ECU harness connector terminals 15 and 12.

Continuity
Should exist.

8. Using a ohm meter, check for continuity between relay harness terminal 1 and ECU harness connector terminals 4 and 9.

Continuity
Should exist.

9. Using a ohm meter, check for continuity between relay harness terminal 2 and ECU harness connector terminal 10.

Continuity
Should exist.


If any of the previous tests produce unsatisfactory results, the harness will need to be repaired or replaced. Once repairs have been completed, road test the vehicle to confirm that the repair has corrected the problem.
If the same problem reoccurs, it is possible that there is an intermittent failure of the component or the ECU. Check for looseness at all harness junctions and test for an intermittent failure.