Inspection Procedure 30

Power Supply And Ignition Switch-IG Circuit:

Connectors: A-21X, C-49, C-53, C-60 <M/T>, C-54, C-57 <A/T>:

CIRCUIT OPERATION
- Battery positive voltage is applied to the MFI relay (terminals 3, 4).
- When the ignition switch is turned "ON," the battery positive voltage is applied to the ECM (terminal 82) or PCM (terminal 98) .
When the battery positive voltage is applied, the ECM or PCM turns the power transistor in the ECM or PCM "ON" and grounds the MFI relay coil. With this, the MFI relay turns "ON" and the battery positive voltage is supplied to the ECM (terminals 12, 25) or PCM (terminal 41, 47) from the MFI relay (terminal 1).

- Battery positive voltage is constantly supplied to the ECM (terminal 80) or PCM (terminal 66) as the backup power.
- The ECM (terminals 13, 26) or PCM (terminal 42, 48) is grounded to the vehicle body.

TROUBLESHOOTING HINTS
The most likely causes for this case:
- Malfunction of the ignition switch.
- Malfunction of the MFI relay.
- Improper connector contact, open circuit or short-circuited harness wire.
- Disconnected ECM ground wire.
- Disconnected PCM ground wire.
- Malfunction of the ECM.
- Malfunction of the PCM.

DIAGNOSIS

STEP 1. Check the MFI relay.
1. Remove the MFI relay.
2. Check for continuity between the MFI relay terminals 2 and 4.
- There should be continuity (approximately 70 ohms)

3. Use jumper wires to connect MFI relay terminal 4 to the positive battery terminal and terminal 2 to the negative battery terminal.
4. Check the continuity between the MFI relay terminals 1 and 3 while connecting and disconnecting the jumper wire at the negative battery terminal.
- Should be less than 2 ohms. (Negative battery terminal connected)
- Should be open circuit. (Negative battery terminal disconnected)

5. Install the MFI relay.

If the check above meets the specification go to step 2.

If the check above does not meet the specification, replace the MFI relay. Then confirm that the malfunction symptom is eliminated.

STEP 2. Check the power supply line at the MFI relay connector A-21X.
1. Disconnect connector A-21X and measure at the harness side.
2. Measure voltage between terminal 3 and ground, and terminal 4 and ground.
- Voltage should be approximately 12 volts (battery positive voltage).

If within specifications, go to Step 3.

If not within specifications, repair the harness wire between the MFI relay connector A-21X and battery. Then confirm that the malfunction symptom is eliminated.

STEP 3. Check the ignition switch-IG signal line at the ECM connector C-60 or PCM connector
C-57 .
1. Disconnect connector C-60 or C-57 and measure at the harness side.
2. Turn the ignition switch to "ON" position.
3. Measure voltage between terminal 82 or 98 and ground.
- Voltage should be approximately 12 volts (battery positive voltage).

4. Turn the ignition switch to "LOCK" (OFF) position.

If within specifications, go to Step 4.

If not within specifications, check the harness wire between the ECM or PCM and the ignition switch, and repair or replace. Refer to Harness Connector Inspection. Then confirm that the malfunction symptom is eliminated.

STEP 4. Check the backup power supply line at ECM connector C-60 or PCM connector C-54 .
1. Disconnect connector C-60 or C-54 and measure at the harness side.
2. Measure the voltage between terminal 80 (C-60) or 66 (C-59) and ground.
- Voltage should be approximately 12 volts (battery positive voltage).

If within specifications, go to Step 5.

If not within specifications, check the harness wire and connector between the ECM or PCM and the battery, and repair or replace. Refer to Harness Connector Inspection. Then confirm that the malfunction symptom is eliminated.

STEP 5. Check the ground line at ECM connector
C-49 or PCM connector C-54 .
1. Disconnect connector C-49 or C-54 and measure at the harness side.
2. Check for continuity between terminals 13, 26 (C-49) and ground .
Check for continuity between terminals 42, 48 (C-54) and ground .
- Should be less than 2 ohms.

If open circuit, go to Step 6.

If less than 2 ohms, repair the harness wire between the ECM connector C-49 or PCM connector C-54 and the ground. Then confirm that the malfunction symptom is eliminated.

STEP 6. Check the circuits at ECM connector C-49, C-53 or PCM connector C-54 .
1. Disconnect connector C-53 or C-54 and check at the harness side.
2. Using a jumper wire, connect ECM connector C-53 terminal 38 (C-53) or PCM connector C-54 terminal 49 (C-54) to ground, and activate the MFI relay.
- An operation sound should be heard from the MFI relay.

3. Disconnect connector C-49 or C-54 and measure at the harness side.

4. Measure voltage between terminals 12, 25 or 41, 47 and ground.
- The voltage should be approximately 12 volts (battery positive voltage) when connector C-53 terminal 38 (C-49) or C-54 terminal 49 (C-54) is grounded.

If within specifications, go to Step 7.

If not within specifications, repair the harness between ECM connector C-49 or PCM connector C-54 and MFI relay connector A-21X. Then confirm that the malfunction symptom is eliminated.

STEP 7. Check harness connectors C-49, C-53 and C-60 at the ECM or harness connectors C-54 and C-57 at the PCM for damage.
If harness connectors C-49, C-53, C-60 or C-54, C-57 are in good condition, replace the ECM or PCM.

If harness connectors C-49, C-53, C-60 or C-54, C-57 are damaged, repair or replace it. Refer to Harness Connector Inspection.

Then confirm that the malfunction symptom is eliminated.