Inspection Procedure 28

Power Supply And Ignition Switch-IG Circuit:

Connectors:

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 PCM (terminal 98).
When the battery positive voltage is applied, the PCM turns the power transistor in the control module "ON" and grounds the MFI relay coil. With this, the MFI relay turns "ON" and the battery positive voltage is supplied to the PCM (terminal 41, 47) from the MFI relay (terminal 1).

- A battery positive voltage is constantly supplied to the PCM (terminal 66) as the backup power.
- The 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 PCM ground wire.
- 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.

- When the jumper wire is connected to the negative battery terminal, the continuity is (0 ohms) and when disconnected, the continuity is gone.

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 C-59.
1. Disconnect connector C-59 and measure at the harness side.




2. Connect terminal 3 and ground, and terminal 4 and ground via a 20-ohms resistor.

Measure the current at this time.
- The current should be 0.5 ampere or more.

If within specifications, go to Step 3.

If not within specifications, repair the harness wire between the MFI relay connector C-59 and fusible link (2). Then confirm that the malfunction symptom is eliminated.

STEP 3. Check the ignition switch-IG signal line at the PCM connector C-91.
1. Disconnect connector C-91 and measure at the harness side.
2. Turn the ignition switch "ON".




3. Measure voltage between terminal 98 and ground.
- Voltage should be approximately 12 volts (battery positive voltage).

4. Turn the ignition switch "OFF".
If within specifications, go to Step 4.

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

STEP 4. Check the backup power supply line at the PCM connector C-90.
1. Disconnect connector C-90 and measure at the harness side.




2. Measure the voltage between terminal 66 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 PCM and the fusible link (6), and repair or replace. Refer to vehicle level Testing and Inspection. Then confirm that the malfunction symptom is eliminated.

STEP 5. Check the ground line at the PCM connector C-90.
1. Disconnect the connector C-90 and measure at the harness side.




2. Check for continuity between terminal 42, 48 and ground.

- There should be continuity (0 ohms).

If continuity, go to Step 6.

If no continuity, repair the harness wire between the PCM connector C-90 and the ground. Then confirm that the malfunction symptom is eliminated.




STEP 6. Check the circuits at the PCM connector C-90.
1. Disconnect connector C-90 and check at the harness side.
2. Using a jumper wire, connect terminal 49 to ground, and activate the MFI relay.

- An operation sound should be heard from the MFI relay.




3. Measure voltage between terminal 41, 47 and ground.
- The voltage should be approximately 12 volts (battery positive voltage) when terminal 49 is grounded.

If within specifications, go to Step 7.

If not within specifications, check the intermediate connector C-14, and repair or replace if needed. Refer to vehicle level Testing and Inspection. If the intermediate connector C-14 is in good condition, repair the harness between the PCM connector C-90 and the MFI relay connector C-59. Then confirm that the malfunction symptom is eliminated.




STEP 7. Check harness connectors C-90, C-91 at the PCM for damage.
If harness connectors C-90, C-91 are damaged, repair or replace it. Refer to vehicle level Testing and Inspection.

If harness connectors C-90, C-91 are in good condition, replace the PCM.

Then confirm that the malfunction symptom is eliminated.