Inspection Procedure 29

Power supply system and ignition switch - IG system.

Power Supply And Ignition Switch - IG Circuit:

Connectors:

CIRCUIT OPERATION
- Battery positive voltage is applied to the MFI relay (terminals 1, 2).
- When the ignition switch is turned to the "ON" position, 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 PCM "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 4).
- A battery positive voltage is constantly supplied to the PCM (terminal 66) as the backup power.
- The PCM (terminals 42, 48) is grounded to the vehicle body.

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- 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 connector A-18X at MFI relay for damage.

Q: Is the connector in good condition?

YES: Go to Step 2.

NO: Repair or replace it. Refer to Harness Connector Inspection. Then confirm that the malfunction symptom is eliminated.










STEP 2. Check the MFI relay.
1. Remove the MFI relay.
2. Check for continuity between the MFI relay terminals 2 and 3.
- There should be continuity, (approximately 70 ohms)
3. Use jumper wires to connect MFI relay terminal 2 to the positive battery terminal and terminal 3 to the negative battery terminal.
4. Check the continuity between the MFI relay terminals 1 and 4 while connecting and disconnecting the jumper wire at the negative battery terminal.
- Should be less than 2 ohm. (Negative battery terminal connected)
- Should be open loop. (Negative battery terminal disconnected)

5. Install the MFI relay.

Q: Is the voltage normal?

YES: Go to Step 3.

NO: Replace the MFI relay. Then confirm that the malfunction symptom is eliminated.




STEP 3. Check the power supply voltage at MFI relay harness side connector A-18X.
1. Disconnect the connector A-18X and measure at the harness side.
2. Measure the voltage between terminal 1, 2 and ground.
- Voltage should be battery positive voltage.

Q: Is the voltage normal?

YES: Go to Step 4.

NO: Check harness connector C-04 at intermediate connector for damage, and repair or replace as required. Refer to Harness Connector Inspection. If intermediate connector is in good condition, repair harness wire between fusible link (3) and MFI relay connector A-18X terminal 1, 2 because of open circuit. Then confirm that the malfunction symptom is eliminated.




STEP 4. Check connector C-40 and C-41 at PCM for damage.

Q: Is the connector in good condition?

YES: Go to Step 5.

NO: Repair or replace it. Refer to Harness Connector Inspection. Then confirm that the malfunction symptom is eliminated.




STEP 5. Check the ignition switch-IG signal voltage at PCM harness side connector C-41.
1. Disconnect the connector C-41 and measure at the harness side.
2. Turn the ignition switch to the "ON" position.
3. Measure the voltage between terminal 98 and ground.
- Voltage should be battery positive voltage.
4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the voltage normal?

YES: Go to Step 6.

NO: Check harness connector C-04, C-66, C-84 and C-87 at intermediate connector for damage, and repair or replace as required. Refer to Harness Connector Inspection. If intermediate connectors are in good condition, repair harness wire between ignition switch connector C-58 terminal 2 and PCM connector C-41 terminal 98 because of open circuit. Then confirm that the malfunction symptom is eliminated.




STEP 6. Check the backup power supply voltage at PCM harness side connector C-40.
1. Disconnect the connector C-40 and measure at the harness side.
2. Measure the voltage between terminal 66 and ground.
- Voltage should be battery positive voltage.

Q: Is the voltage normal?

YES: Go to Step 7.

NO: Check harness connector C-17 and C-66 at intermediate connector for damage, and repair or replace as required. Refer to Harness Connector Inspection. If intermediate connectors are in good condition, repair harness wire between fusible link (18) and PCM connector C-40 terminal 66 because of open circuit. Then confirm that the malfunction symptom is eliminated.




STEP 7. Check the continuity at PCM harness side connector C-40.
1. Disconnect the connector C-40 and measure at the harness side.
2. Check for the continuity between terminal (42, 48) and ground.
- Should be less than 2 ohm.

Q: Is the continuity normal?

YES: Go to Step 8.

NO: Repair harness wire between PCM connector C-40 terminal (42, 48) and ground because of open circuit. Then confirm that the malfunction symptom is eliminated.




STEP 8. Check the power supply voltage at PCM harness side connector C-40.
1. Disconnect the connector C-40 and measure at the harness side.
2. Measure the voltage between terminal 49 and ground.
- Voltage should be battery positive voltage.

Q: Is the voltage normal?

YES: Go to Step 9.

NO: Repair harness wire between MFI relay connector A-18X terminal 3 and PCM connector C-40 terminal 49 because of open circuit. Then confirm that the malfunction symptom is eliminated.




STEP 9. Check the power supply voltage at PCM harness side connector C-40.
1. Disconnect the connector C-40 and measure at the harness side.
2. Using a jumper wire, connect terminal 49 to ground.
3. Measure the voltage between terminal (41, 47) and ground.
- Voltage should be battery positive voltage.

Q: Is the voltage normal?

YES: Replace the PCM. Then confirm that the malfunction symptom is eliminated.

NO: Repair harness wire between MFI relay connector A-18X terminal 4 and PCM connector C-40 terminal (41, 47) because of open circuit. Then confirm that the malfunction symptom is eliminated.