Inspection Procedure 6: Air Flow Sensor System










OPERATION



  • Power is supplied to the air flow sensor (terminal No. 2) from the ETACS-ECU (terminal No. 5) and is earthed to the engine-ECU (terminal No. 98) from the air flow sensor (terminal No. 3).
  • A power voltage of 5 V is applied to the air flow sensor (terminal No. 4) from the engine-ECU (terminal No. 122).
  • The air flow sensor (terminal No. 5) outputs a sensor signal, which is input into the engine-ECU (terminal No. 76).

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-06 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-06 air flow sensor connector.

  • Disconnect connector, and measure at the harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 2 and earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 4 .
Go to Step 3 .

STEP 3. Connector check: C-317 ETACS-ECU connector

Q. Is the check result normal?


    Check intermediate connector C-128, and repair if necessary. If intermediate connector is normal, check harness between the C-317 (terminal No. 5) ETACS-ECU connector and A-06 (terminal No. 2) air flow sensor connector.

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

STEP 4. Perform resistance measurement at A-06 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 6 .
Go to Step 5 .

STEP 5. Connector check: B-28 engine-ECU connector

Q. Is the check result normal?


    Check harness between the A-06 (terminal No. 3) air flow sensor connector and B-28 (terminal No. 98) engine-ECU connector.

    • Check earthing line for open circuit and damage.
Repair or replace the connector.

STEP 6. Perform voltage measurement at A-06 air flow sensor connector.

  • Disconnect connector, and measure at the harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 4 and earth.
OK: 4.9 - 5.1 V

Q. Is the check result normal?

Go to Step 10 .
Go to Step 7 .

STEP 7. Connector check: B-28 engine-ECU connector

Q. Is the check result normal?
Go to Step 8 .
Repair or replace the connector.

STEP 8. Check harness between A-06 (terminal No. 4) air flow sensor connector and B-28 (terminal No. 122) engine-ECU connector.

  • Check power supply line for open/short circuit.

Q. Is the check result normal?

Go to Step 9 .
Repair the damaged harness wire.

STEP 9. 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 10. Check harness between A-06 (terminal No. 4) air flow sensor connector and B-28 (terminal No. 122) engine-ECU connector.

  • Check power supply line for damage.

Q. Is the check result normal?

Go to Step 11 .
Repair the damaged harness wire.

STEP 11. Check harness between C-317 (terminal No. 5) ETACS-ECU connector and A-06 (terminal No. 2) air flow sensor connector.
note Before checking harness, check intermediate connector C-128, and repair if necessary.

  • Check output line for damage.

Q. Is the check result normal?

Go to Step 12 .
Repair the damaged harness wire.

STEP 12. Check harness between A-06 (terminal No. 5) air flow sensor connector and B-28 (terminal No. 76) engine-ECU connector.

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

Q. Is the check result normal?
Go to Step 13 .
Repair the damaged harness wire.

STEP 13. 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.