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Inspection procedure 22: Power supply system and ignition switch-IG system
 
 
 
 
CIRCUIT OPERATION
  • Battery positive voltage is applied to the MFI relay.
  • When the ignition switch is turned to the "ON" position, battery positive voltage is applied to the ECM terminal IGN. When battery positive voltage is applied, the ECM terminal C/R turns the power transistor in the ECM "ON" and grounds the MFI relay coil. With this, the MFI relay turns "ON" the battery positive voltage is supplied to the ECM terminal BAT1 from the MFI relay.
  • A battery positive voltage is constantly supplied to the ECM terminal BACK as the backup power.
  • The ECM terminals GNDB and GNDE are grounded to the vehicle body.
 
 
COMMENT
  • When the ignition switch "ON" signal is input into the ECM via ETACS-ECU, the ECM turns "ON" the MFI relay. This causes battery positive voltage to be supplied to the ECM, sensor and actuator.
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be stored are:)
  • Ignition switch failed <Vehicles without KOS>
  • IG1 relay failed <Vehicles with KOS>.
  • MFI relay failed.
  • Open or shorted ignition switch-IG circuit, harness damage or connector damage.
  • Open or shorted MFI relay control circuit, harness damage or connector damage.
  • Open or shorted power supply circuit, harness damage or connector damage.
  • Open or shorted battery backup line, harness damage or connector damage.
  • ECM failed.

 
 
DIAGNOSIS
STEP 1. Check the MFI relay.
Refer to MFI Relay Continuity Check .
Is the MFI relay normal?
Go to Step 2.
Replace the MFI relay. Then confirm that the malfunction symptom is eliminated.
 
STEP 2. Measure the power supply voltage at MFI relay harness side connector.
(1) Disconnect the MFI relay and measure at the relay box side.
(2) Measure the voltage between terminals power supply line and ground.
  • Voltage should be battery positive voltage.
Is battery positive voltage (approximately 12 volts) present?
Go to Step 3.
Repair or replace the connector(s), or check and repair the harness of open circuit and short circuit to ground in power supply line between fusible link and MFI relay connector. Then confirm that the malfunction symptom is eliminated.
 
STEP 3. Measure the ignition switch-IG signal voltage at ECM harness side connector.
(1) Disconnect the connector and measure at the harness side.
(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between terminal IGN line and ground.
  • Voltage should be battery positive voltage.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is battery positive voltage (approximately 12 volts) present?
<Vehicles without KOS> : Go to Step 6.
<Vehicles with KOS> : Go to Step 7.
<Vehicles without KOS> : Go to Step 4.
<Vehicles with KOS> : Go to Step 5.
 
STEP 4. Check the ignition switch
Refer to GROUP 54A, ignition switch - Inspection - Ignition Switch Continuity Check .
Are there any abnormalities?
Replace the ignition switch. Then confirm that the malfunction symptom is eliminated.
Repair or replace the connector(s), or check and repair the harness of open circuit and short circuit to ground in power supply line between ignition switch connector and ECM connector. Then confirm that the malfunction symptom is eliminated.
 
STEP 5. Check of open circuit and short circuit to ground between IG1 relay connector and ECM connector.
Is the harness wire in good condition?
Repair or replace the connector(s), or check and repair the harness of open circuit and short circuit to ground in power supply line between IG1 relay connector and ECM connector. Then confirm that the malfunction symptom is eliminated.
Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.
 
STEP 6. Check of harness damage in IGN line between ignition switch connector and ECM connector.
Is the harness wire in good condition?
Go to Step 8.
Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.
 
STEP 7. Check for harness damage in IGN line between IG1 relay connector and ECM connector.
Is the harness wire in good condition?
Go to Step 8.
Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.
 
STEP 8. Measure the power supply voltage at ECM harness side connector.
(1) Disconnect the connector and measure at the harness side.
(2) Measure the voltage between terminal BACK and ground.
  • Voltage should be battery positive voltage.
Is battery positive voltage (approximately 12 volts) present?
Go to Step 9.
Repair or replace the connector(s), or check and repair the harness of open circuit and short circuit to ground in BACK line between fusible link and ECM connector. Then confirm that the malfunction symptom is eliminated.
 
STEP 9. Check the continuity at ECM harness side connector.
(1) Disconnect the connector and measure at the harness side.
(2) Check for the continuity between terminals GNDB, GNDE and ground.
  • Continuity (2 ohms or less).
Does continuity exist?
Go to Step 10.
Repair or replace the connector(s), or check and repair the harness of open circuit and damage in GNDB, GNDE line between ECM connector and body ground. Then confirm that the malfunction symptom is eliminated.
 
STEP 10. Measure the power supply voltage at ECM harness side connector.
(1) Disconnect the connector and measure at the harness side.
(2) Measure the voltage between terminal C/R and ground.
  • Voltage should be battery positive voltage.
Is battery positive voltage (approximately 12 volts) present?
Go to Step 11.
Repair or replace the connector(s), or check and repair the harness of open circuit and short circuit to ground in C/R line between MFI relay connector and ECM connector. Then confirm that the malfunction symptom is eliminated.
 
STEP 11. Measure the power supply voltage at ECM harness side connector.
(1) Disconnect the connector and measure at the harness side.
(2) Short-circuit the terminal C/R line of the ECM harness connector to the ground.
(3) Measure the voltage between terminal BAT1 and ground.
  • Voltage should be battery positive voltage.
Is battery positive voltage (approximately 12 volts) present?
Go to Step 14.
Go to Step 12.
 
STEP 12. Check of open circuit and short circuit to ground in BAT1 line between MFI relay connector and ECM connector.
Is the harness wire in good condition?
Go to Step 13.
Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.
 
STEP 13. Check of harness damage in power supply line between fusible link and MFI relay connector.
Is the harness wire in good condition?
Repair or replace the connector(s), or check and repair the harness of damage in C/R line between MFI relay connector and ECM connector. Then confirm that the malfunction symptom is eliminated.
Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.
 
STEP 14. Check of harness damage in BAT1 line between MFI relay connector and ECM connector.
Is the harness wire in good condition?
Replace the ECM (Refer to, Removal and Installation ). Then confirm that the malfunction symptom is eliminated.
Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.