Inspection Procedure 29
Power Supply And Ignition Switch-IG Circuit:
CIRCUIT OPERATION
- Battery positive voltage is applied to the MFI relay (terminals 3, 4).
- When the ignition switch is turned to "ON" position, the battery positive voltage is applied to the ECM (terminal 99)
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 47, 59)
- Battery positive voltage is constantly supplied to the ECM (terminal 60)
- The ECM (terminals 46, 58)
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 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 battery positive voltage.
If within specifications, go to Step 3.
If not within specifications, repair the harness wire between 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 ECM connector C-62
1. Disconnect connector C-62
2. Turn the ignition switch to ON" position.
3. Measure voltage between terminal 99
- Voltage should be 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-58
1. Disconnect connector C-58
2. Measure the voltage between terminal 60
- Voltage should be battery positive voltage. If within specifications, go to Step 5.
If not within specifications, check the harness wire and connector between the ECM
STEP 5. Check the ground line at ECM connector C-58
1. Disconnect connector C-58
2. Check for continuity between terminals 46, 58 and ground
Check for continuity between terminals 42, 48 and ground .
- Should be less than 2 ohms . If less than 2 ohms , go to Step 6.
If open circuit, repair the harness wire between the ECM connector C-58
STEP 6. Check the circuits at ECM connector C-58
1. Disconnect connector C-58
2. Using a jumper wire, connect ECM connector C-58 terminal 57
- An operation sound should be heard from the MFI relay.
3. Measure voltage between terminals 47, 59
- The voltage should be battery positive voltage when connector C-58 terminal 57
If within specifications, go to Step 7.
If not within specifications, repair the harness between ECM connector C-58
STEP 7. Check harness connectors C-58 and C-62 at the ECM
If harness connectors C-58, C-62
If harness connectors C-58, C-62
Then confirm that the malfunction symptom is eliminated.