Checking The PCM Power And Grounds

CONTROL RELAY
Failure of the control relay could interrupt power supply to the fuel pump, injectors and ECM, 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.

Fig. 1 Relay Test:

1. Supply 12 VDC to relay terminals 8 (-) and 10 (+). Using a voltmeter, check for voltage between terminals 4 (+) and 8 (-) and between terminals 5 (+) and 8 (-). Refer to Fig. 1.

Voltage
12 VDC

Fig. 2 Relay Test:

2. Supply 12 VDC to relay terminals 6 (-) and 9 (+). Using an ohmmeter, check for continuity between terminals 2 and 3. Refer to Fig. 2.

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

Fig. 3 Relay Test:

3. Supply 12 VDC to relay terminals 7 (-) and 3 (+). Using a voltmeter, check for voltage between terminals 2 (+) and supply battery ground terminal. Refer to Fig. 3.

Voltage
12 VDC when terminal 7 is connected.
0 VDC when terminal 7 is NOT connected.

Power Supply Circuit:

KEY "ON" POWER CIRCUIT
1. Disconnect the negative battery cable and the ECM connector.
2. Reconnect the negative battery cable and turn the key to the ON position.
3. Using a volt meter, check for voltage between ECM harness connector terminal 110 and ground.

Voltage
System voltage.

4. Turn the key to the OFF position and disconnect the control relay.
5. Using a volt meter, check for voltage between relay harness connector terminal 10 and ground.

Voltage
System voltage.

6. Disconnect the negative battery cable and the ECM connector.
7. Using an ohm meter check for continuity between relay harness connector 8 and ECM harness connectors 63 and 66.

Continuity
Should exist.

8. Using an ohm meter check for continuity between relay harness connector 4 and ECM harness connectors 102 and 107.

Continuity
Should exist.

9. Using an ohm meter check for continuity between relay harness connector 5 and ECM harness connectors 102 and 107.

Continuity
Should exist.

9. Using an ohm meter check for continuity between relay harness connector 4 and ground.

Continuity
Should not exist.


10. Using an ohm meter check for continuity between relay harness connector 5 and ground.

Continuity
Should not exist.

Back-up And Voltage Signal Circuit:

KEY "OFF" POWER CIRCUIT
1. Using a volt meter, check the voltage between ECM harness terminal 103 and ground.

Voltage
System voltage.

2. Disconnect the negative battery cable and the ECM connector.
3. Using an ohm meter, check for continuity between the positive battery terminal and ECM harness terminal 103.

Continuity
Should exist.

4. Using an ohm meter, check for continuity between chassis ground (not the negative battery terminal) and ECM harness terminal 103.

Continuity
Should not exist.

ECU Ground Circuit:

GROUND CIRCUIT
1. Disconnect the ECM connector.
2. Using an ohm meter, check for continuity between ECM harness terminal 101 and ground.

Continuity
Should exist.

3. Using an ohm meter, check for continuity between ECM harness terminal 106 and ground.

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 ECM. Check for looseness at all harness junctions and test for an intermittent failure.