Inspection Procedure 21: Engine-ECU Power Supply, Engine Control Relay, Ignition Switch-IG1 System

OPERATION

The battery voltage is applied to the engine control relay (terminal No. 1 and No. 3).
The engine-ECU (terminal No. 107) 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 (terminal No. 77 and No. 92), the sensor and the actuator from the engine control relay (terminal No. 4).
The engine-ECU (terminal No. 75 and No. 76) is earthing to the vehicle body.

FUNCTION

When the ignition switch ON signal is input to the engine-ECU, the engine-ECU places the engine control relay in the ON position. Accordingly, the battery voltage is supplied to the engine-ECU, sensor and actuator.

PROBABLE CAUSES

Failed engine control relay
Open/short circuit and damage in engine control relay circuit or loose connector contact
Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Check battery voltage.

Measure battery voltage during cranking.

OK: 8 V or more

Q. Is the check result normal?

	Go to Step 2 .

	Check battery (Refer to GROUP 54A - Battery - On-vehicle Service - Battery test ).

STEP 2. Connector check: B-206 engine control relay connector

Q. Is the check result normal?

Go to Step 3 .

Repair or replace the connector.

STEP 3. Check engine control relay.

Check engine control relay (Refer to ).

Q. Is the check result normal?

	Go to Step 4 .

	Replace the engine control relay.

STEP 4. Perform voltage measurement at B-206 engine control relay connector.

Remove relay, and measure at J/B side.
Voltage between terminal No. 1 and earth, also between terminal No. 3 and earth.

OK: System voltage

Q. Is the check result normal?

Go to Step 5 .

Check power supply line for open/short circuit.

STEP 5. Connector check: A-35 engine-ECU connector.

Q. Is the check result normal?

Go to Step 6 .

Repair or replace the connector.

STEP 6. Perform voltage measurement at A-35 engine-ECU connector.

Disconnect engine-ECU connector, and connect special tool power plant ECU check harness (MB991987), and then measure the voltage on the check connector.
Ignition switch: ON
Voltage between terminal No. 77 and earth also between terminal No. 92 and earth.

OK: System voltage

Q. Is the check result normal?

Check earthing line for short circuit.

Go to Step 7 .

STEP 7. Check harness between B-206 (terminal No. 2) engine control relay connector and A-35 (terminal No. 77 and terminal No. 92) engine-ECU connector.

note

Before checking harness, check intermediate connector B-212 and repair if necessary.

Check output line for open/short circuit and damage.

Q. Is the check result normal?

Go to Step 8 .

Repair the damaged harness wire.

STEP 8. Perform voltage measurement at A-35 engine-ECU connector.

Disconnect connector and measure at harness side.
Ignition switch: ON
Voltage between terminal No. 122 and earth.

OK: System voltage

Q. Is the check result normal?

Go to Step 11 .

Go to Step 9 .

STEP 9. Connector check: B-240 ignition switch connector

Q. Is the check result normal?

Go to Step 10 .

Repair or replace the connector.

STEP 10. Check ignition switch.

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

Q. Is the check result normal?

Check output line for open/short circuit.

Replace the ignition switch.

STEP 11. Check harness between B-206 (terminal No. 2) engine control relay connector and A-35 (terminal No. 107) engine-ECU connector.

note

Before checking harness, check intermediate connector B-212, and repair if necessary.

Check power supply line for open circuit damage.

Q. Is the check result normal?

Go to Step 12 .

Repair the damaged harness wire.

STEP 12. Check harness between B-206 (terminal No. 1 and No. 3) engine control relay connector and battery.

note

Before checking harness, check intermediate connector B-208, and repair if necessary.

Check power supply line for damage.

Q. Is the check result normal?

Go to Step 13 .

Repair the damaged harness wire.

STEP 13. Check harness between B-240 (terminal No. 2) ignition switch connector and A-35 (terminal No. 122) engine-ECU connector.

Check output line for damage.

Q. Is the check result normal?

Go to Step 14 .

Repair the damaged harness wire.

STEP 14. Check harness between A-35 engine-ECU connector and body earth.

Check and repair harness between A-35 (terminal N0. 75) engine-ECU connector and body earth.
Check and repair harness between A-35 (terminal No. 76) engine-ECU connector and body earth.

note

Before checking harness, check intermediate connector A-14, and repair if necessary.

Check earthing line for open circuit damage.

Q. Is the check result normal?

Replace the engine-ECU then perform the variant coding (Refer to GROUP 00 - Precautions Before Service - How to Perform Variant Coding

Repair the damaged harness wire.