Inspection Procedure 7: Air Flow Sensor System










OPERATION



  • Power is supplied to the air flow sensor (terminal No. 4) from the engine control relay 1 (terminal No. 2) and is earthed to the engine-ECU (terminal No. 10) from the air flow sensor (terminal No. 3).
  • The air flow sensor (terminal No. 1) outputs a sensor signal, which is input into the engine-ECU (terminal No. 29).

FUNCTION



  • The air flow sensor outputs pulse signal that varies in accordance with the intake air volume.
  • In response to the signal, the engine-ECU controls fuel injection control, etc.

PROBABLE CAUSES



  • Failed air flow sensor
  • Open/short circuit or harness damage in air flow sensor circuit or loose connector contact
  • Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Connector check: A-08 air flow sensor connector

Q. Is the check result normal?

Go to Step 2 .
Repair or replace the connector.

STEP 2. Perform voltage measurement at A-08 air flow sensor connector.

  • Disconnect connector, and measure at the harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 4 and earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 4 .
Go to Step 3 .

STEP 3. Connector check: A-33X engine control relay 1 connector

Q. Is the check result normal?


    Check harness between the A-33X (terminal No. 2) engine control relay 1 connector and A-08 (terminal No. 4) air flow sensor connector.

    • Check power supply line for open/short circuit.
Repair or replace the connector.

STEP 4. Perform resistance measurement at A-08 air flow sensor.

  • Disconnect connector, and measure at the harness side.
  • Resistance between terminal No. 3 and earth.
OK: Continuity (2 Ω or less)

Q. Is the check result normal?

Go to Step 8 .
Go to Step 5 .

STEP 5. Connector check: B-18 engine-ECU connector

Q. Is the check result normal?
Go to Step 6 .
Repair or replace the connector.

STEP 6. Check harness between A-08 (terminal No. 3) air flow sensor connector and B-18 (terminal No. 69) engine-ECU connector.

  • Check earthing line for open circuit and damage.

Q. Is the check result normal?

Go to Step 7 .
Repair the damaged harness wire.

STEP 7. Check the trouble symptoms.

Q. Does trouble symptom persist?

Replace the engine-ECU.
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).

STEP 8. Check harness between A-33X (terminal No. 2) engine control relay 1 connector and A-08 (terminal No. 4) air flow sensor connector.

  • Check power supply line for damage.

Q. Is the check result normal?

Go to Step 9 .
Repair the damaged harness wire.

STEP 9. Check harness between A-08 (terminal No. 1) air flow sensor connector and B-18 (terminal No. 29) engine-ECU connector.

  • Check output line for open/short circuit and damage.

Q. Is the check result normal?
Go to Step 10 .
Repair the damaged harness wire.

STEP 10. Replace the air flow sensor.



  • After replacing the air flow sensor, re-check the trouble symptoms.

Q. Does trouble symptom persist?
Replace the engine-ECU.
The check is end.