Inspection Procedure 19: Engine-ECU Power Supply, Engine Control Relay, Ignition Switch-IG1 System

OPERATION

Battery voltage is applied to the engine control relay.
Engine-ECU connector terminal C/R applies current to the engine control relay coil by turning ON the power transistor in the unit in order to turn the relay ON.
When the engine control relay is turned ON, the battery power will be supplied from the engine control relay to the engine-ECU, sensor and actuator.

FUNCTION

When the ignition switch ON signal is input into the engine-ECU via ETACS-ECU, the engine-ECU turns ON the engine control relay. This causes battery voltage to be supplied to the engine-ECU, sensor and actuator.

PROBABLE CAUSES

Failed battery
Failed engine control relay
Failed ignition switch <Vehicles without KOS>
Failed KOS&OSS-ECU <Vehicles with KOS>
Open/short circuit or harness damage in engine control relay circuit, or loose connector contact.
Open/short circuit or harness damage in ignition switch (IG1) circuit, or loose connector contact.
Open circuit or harness damage in engine-ECU earth circuit, or loose connector contact.
Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Check battery.

Battery check (Refer to GROUP 54A - Battery - On-vehicle Service - Battery Test ).

Q. Is the check result normal?

	Go to Step 2.

	Replace the battery.

STEP 2. Check engine control relay itself.

Engine control relay continuity check (Refer to ).

Q. Is the check result normal?

	Go to Step 3.

	Replace the engine control relay.

STEP 3. Perform voltage measurement at engine control relay connector

Remove relay, and measure at relay box side.
Voltage between terminal battery line and earth

OK: System voltage

Q. Is the check result normal?

	Go to Step 4.

	Repair or replace the connector(s), or check and repair the harness of open circuit in power supply line between battery and engine control relay connector.

STEP 4. Perform voltage measurement at engine-ECU connector.

Disconnect connector, and measure at harness side.
Voltage between terminal C/R line and earth.

OK: System voltage

Q. Is the check result normal?

	Go to Step 5.

	Repair or replace the connector(s), or check and repair the harness of open circuit in C/R line between engine control relay connector and engine-ECU connector.

STEP 5. Perform voltage measurement at engine-ECU connector.

Disconnect connector, and measure at harness side.
Short-circuit engine-ECU harness side connector terminal C/R line to the earth.
Voltage between terminal BAT1 line and earth.

OK: System voltage

Q. Is the check result normal?

	Go to Step 8.

	Go to Step 6.

STEP 6. Check of short to earth, and open circuit in BAT1 line between engine control relay connector and engine-ECU connector.

Q. Is the check result normal?

	Go to Step 7.

	Repair the connector(s) or wiring harness.

STEP 7. Check of damage in C/R line between the battery and engine control relay connector.

Q. Is the check result normal?

	Repair or replace the connector(s), or check and repair the harness of damage in C/R line between engine control relay connector and engine-ECU connector.

	Repair the connector(s) or wiring harness.

STEP 8. Check of damage in BAT1 line between engine-ECU connector and engine control relay connector.

Q. Is the check result normal?

	Go to Step 9.

	Repair the connector(s) or wiring harness.

STEP 9. Check of damage in power supply line between battery and engine control relay connector.

Q. Is the check result normal?

	Go to Step 10.

	Repair the connector(s) or wiring harness.

STEP 10. Perform voltage measurement at engine-ECU connector.

Disconnect connector, and measure at harness side.
Ignition switch: ON
Voltage between terminal IGN and earth.

OK: System voltage

Q. Is the check result normal?

	YES : Go to Step 14 <Vehicles without KOS>.

	YES : Go to Step 15 <Vehicles with KOS>.

	Go to Step 11 <Vehicles without KOS>.

	Go to Step 12 <Vehicles with KOS>.

STEP 11. Check ignition switch itself.

Check ignition switch itself (Refer to GROUP 54A - Ignition switch - Inspection - Ignition Switch Check ).

Q. Is the check result normal?

	Repair or replace the connector(s), or check and repair the harness of short to earth, and open circuit in IGN line ignition switch connector and engine-ECU connector.

	Replace the ignition switch.

STEP 12. Check IG1 relay itself.

Check IG1 relay itself (Refer to GROUP 42B - On-vehicle Service - Relay Inspection ).

Q. Is the check result normal?

	Go to Step 13.

	Replace the IG1 relay.

STEP 13. Check of short to earth, and open circuit in IG1 line between IG1 relay connector and engine-ECU connector.

Q. Is the check result normal?

	Perform troubleshooting of OSS System (Refer to GROUP 42B - Troubleshooting - Trouble Symptom Chart ).

	Repair the connector(s) or wiring harness.

STEP 14. Check of damage in IGN line between ignition switch connector and engine-ECU connector.

Q. Is the check result normal?

	Go to Step 16.

	Repair the connector(s) or wiring harness.

STEP 15. Check of damage in IGN line between IG1 relay connector and engine-ECU connector.

Q. Is the check result normal?

	Go to Step 16.

	Repair the connector(s) or wiring harness.

STEP 16. Check of open circuit, and damage in GNDB, GNDE line between engine-ECU connector and body earth.

Q. Is the check result normal?

	Replace the engine-ECU.

	Repair the connector(s) or wiring harness.