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Inspection procedure 21: 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 case: )
  • Battery failed.
  • Ignition switch failed <Vehicles without KOS>
  • KOS&OSS-ECU 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.
  • ETACS-ECU failed.
  • ECM failed.

 
 
DIAGNOSIS
STEP 1. Check the battery.
Refer to GROUP 54A, Battery - On-vehicle Service - Battery Test .
Are there any abnormalities?
Replace the battery. Then confirm that the malfunction symptom is eliminated.
Go to Step 2.
 
STEP 2. Check the MFI relay.
Refer to MFI Relay Continuity Check .
Is the MFI relay normal?
Go to Step 3.
Replace the MFI relay. Then confirm that the malfunction symptom is eliminated.
 
STEP 3. Measure the power supply voltage at MFI relay harness side connector.
(1) Remove 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 4.
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 4. Measure the ignition switch-IG signal voltage at ECM harness side connector.
(1) Disconnect the ECM 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?
Go to Step 9.
Go to Step 5.
 
STEP 5. Measure the ignition switch-IG signal voltage at ETACS-ECU harness side connector.
(1) Disconnect the ETACS-ECU connector and measure at the harness side.
(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between terminal IGS 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?
Go to Step 8.
: Go to Step 6.
: Go to Step 7.
 
STEP 6. 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 short to ground and open circuit in IG1 to IGS line between ignition switch connector and ETACS-ECU connector. Then confirm that the malfunction symptom is eliminated.
 
STEP 7. Check of short to ground and open circuit in IG1 to IGS line between KOS&OSS-ECU connector and ETACS-ECU connector.
Is the harness wire in good condition?
Check the OSS System. Refer to GROUP 42B, Diagnosis - Trouble Symptom Chart .
Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.
 
STEP 8. Check the continuity at ETACS-ECU side connectors.
(1) Disconnect the ETACS-ECU connector and measure at the ETACS-ECU side.
(2) Check for the continuity between terminal IGS and EIG1.
noteConnect the (+) side of circuit tester to terminal EIG1.
  • Continuity
Does continuity exist?
Repair or replace the connector(s), or check and repair the harness of short to ground and open circuit in EIG1 to IGN line between ETACS-ECU connector and ECM connector. Then confirm that the malfunction symptom is eliminated.
Replace the ETACS-ECU. Then confirm that the malfunction symptom is eliminated.
 
STEP 9. Check the continuity at ETACS-ECU side connectors.
(1) Disconnect the ETACS-ECU connector and measure at the ETACS-ECU side.
(2) Check for the continuity between terminal IGS and EIG1.
noteConnect the (+) side of circuit tester to terminal EIG1.
  • Continuity
Does continuity exist?
: Go to Step 10.
: Go to Step 11.
Replace the ETACS-ECU. Then confirm that the malfunction symptom is eliminated.
 
STEP 10. Check of harness damage in IG1 to IGS line between ignition switch connector and ETACS-ECU connector.
Is the harness wire in good condition?
Go to Step 12.
Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.
 
STEP 11. Check for harness damage in IG1 to IGS line between KOS&OSS-ECU connector and ETACS-ECU connector.
Is the harness wire in good condition?
Go to Step 12.
Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.
 
STEP 12. Check for harness damage in EIG1 to IGN line between ETACS-ECU 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. Measure the backup power supply voltage at ECM harness side connector.
(1) Disconnect the ECM 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 14.
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 14. Check the continuity at ECM harness side connector.
(1) Disconnect the ECM 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 15.
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 ground. Then confirm that the malfunction symptom is eliminated.
 
STEP 15. Measure the power supply voltage at ECM harness side connector.
(1) Disconnect the ECM 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 16.
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 16. Measure the power supply voltage at ECM harness side connector.
(1) Disconnect the ECM connector and measure at the harness side.
(2) Short-circuit the terminal C/R 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 19.
Go to Step 17.
 
STEP 17. Check of short to ground and open circuit in BAT1 line between MFI relay connector and ECM connector.
Is the harness wire in good condition?
Go to Step 18.
Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.
 
STEP 18. 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 19. 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.