Inspection Procedure 16: Engine-ECU Power Supply System

OPERATION

The battery voltage is applied to the engine control relay connector terminal.
The engine-ECU connector terminal C/R makes the power transistor in the unit be in "ON" position and makes currents go on the engine control relay coil, and that makes the relay be in "ON" position.
When the engine control relay is in "ON" position, the battery voltage is supplied to the engine-ECU connector terminal BAT1 and terminal BAT2, the sensor and the actuator from the engine control relay connector terminal.
The engine-ECU connector terminal GNDB, terminal GNDE and terminal SGND is earthing to the vehicle body.

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 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 ETACS-ECU
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 connector check.
Engine control relay continuity check (Refer to ).

Q. Is the check result normal?

	Go to Step 3.

	Repair or replace the connector, or 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 power supply lines and body earth

OK: System voltage

Q. Is the check result normal?

	Go to Step 4.

	Repair or replace the connector, or check and repair harness between battery and engine control relay connector terminal. Check power supply line for open/short circuit.

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

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

OK: System voltage

Q. Is the check result normal?

	Go to Step 5.

	Repair or replace the connector, or check and repair harness between engine control relay connector terminal and engine-ECU connector terminal C/R. Check signal line for open/short circuit.

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

Disconnect connector, and measure at harness side.
Short-circuit engine-ECU connector terminal C/R to the body earth.
Voltage between terminal BAT1, BAT2 and body earth.

OK: System voltage

Q. Is the check result normal?

	Go to Step 8.

	Go to Step 6.

STEP 6. Check harness between engine control relay connector terminal and engine-ECU connector terminal BAT1, BAT2.

Check output line for open/short circuit.

Q. Is the check result normal?

	Go to Step 7.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 7. Check harness between the battery and engine control relay connector terminal.

Check power supply line for damage.

Q. Is the check result normal?

	Repair or replace the connector, or check and repair harness between engine control relay connector terminal and engine-ECU connector terminal C/R. Check signal line for damage.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 8. Check harness between engine-ECU connector terminal BAT1, BAT2 and engine control relay connector terminal.

Check output line for damage.

Q. Is the check result normal?

	Go to Step 9.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 9. Check harness between battery and engine control relay connector terminal.

Check power supply line for damage.

Q. Is the check result normal?

	Go to Step 10.

	Repair or replace the connector, or repair the damaged harness wire.

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

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

OK: System voltage

Q. Is the check result normal?

	YES : Go to Step 15 <Vehicles without KOS>.

	YES : Go to Step 16 <Vehicles with KOS>.

	Go to Step 11.

STEP 11. Perform voltage measurement at ETACS-ECU connector.

Disconnect connector, and measure at harness side.
Ignition switch: ON
Voltage between terminal IG1 and body earth.

OK: System voltage

Q. Is the check result normal?

	Go to Step 14.

	NO : Go to Step 12 <Vehicles without KOS>.

	NO : Go to Step 13 <Vehicles with KOS>.

STEP 12. Check ignition switch itself.

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

Q. Is the check result normal?

	Repair or replace the connector, or check and repair harness between ignition switch connector terminal and ETACS-ECU connector terminal IG1. Check signal line for open/short circuit.

	Repair or replace the connector, or replace the ignition switch.

STEP 13. Check harness between OSS-ECU connector terminal IG1 and ETACS-ECU connector terminal IG1.

Check power supply line for open/short circuit.

Q. Is the check result normal?

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

	Repair or replace the connector, or repair the damaged harness wire.

STEP 14. Continuity check on ETACS-ECU connectors

Disconnect connectors, and measure at the ETACS-ECU side.
Continuity test between terminal IG1 and IGN.

note

Connect the (+) side of circuit tester to terminal IGN.

OK: Continuity

Q. Is the check result normal?

	Repair or replace the connector, or check and repair harness between ETACS-ECU connector terminal IGN and engine-ECU connector terminal IGN. Check signal line for open/short circuit.

	Repair or replace the connector, or replace the ETACS-ECU.

STEP 15. Check harness between ignition switch connector terminal and ETACS-ECU connector terminal IG1.

Check signal line for damage.

Q. Is the check result normal?

	Go to Step 17.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 16. Check harness between OSS-ECU connector terminal IG1 and ETACS-ECU connector terminal IG1.

Check signal line for damage.

Q. Is the check result normal?

	Go to Step 17.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 17. Continuity check on ETACS-ECU connectors

Disconnect connectors, and measure at the ETACS-ECU side.
Continuity test between terminal IG1 and IGN.

note

Connect the (+) side of circuit tester to terminal IGN.

OK: Continuity

Q. Is the check result normal?

	Go to Step 18.

	Repair or replace the connector, or replace the ETACS-ECU.

STEP 18. Check harness between ETACS-ECU connector terminal IGN and engine-ECU connector terminal IGN.

Check signal line for damage.

Q. Is the check result normal?

	Go to Step 19.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 19. Check harness between engine-ECU connector terminal GNDB, GNDE, SGND and body earth.

Check earthing line for open circuit and damage.

Q. Is the check result normal?

	Replace the engine-ECU.

	Repair or replace the connector, or repair the damaged harness wire.