Code No. P0102: Air flow Sensor Circuit Low Input


OPERATION



  • Power is supplied by the engine control relay (terminal No. 2) to the air flow sensor (terminal No. 3), and the air flow sensor (terminal No. 2) is earthed through the engine-ECU (terminal No. 155).
  • The air flow sensor (terminal No. 1) outputs a sensor signal, which is input into the engine-ECU (terminal No. 140).

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 EGR control, etc.

TROUBLE JUDGMENT


Check Conditions
  • Battery positive voltage is 8 - 16 V
  • 2 seconds later after the ignition switch has been in "ON" position or the engine has started up.
Judgment Criterion
  • The air flow sensor output voltage is 0.50 V or less.

FAIL-SAFE AND BACKUP FUNCTION



  • The control is performed using the previous value.
  • The DPF regeneration is prohibited.
  • The throttle valve is opened (Electrical discontinuity).
  • The EGR control is stopped (fully closed).
  • The AS&G control is prohibited.

PROBABLE CAUSES



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

DIAGNOSTIC PROCEDURE

STEP 1. M.U.T.-III data list

  • Refer to Data List Reference Table .

  1. Item 114: Air flow sensor

Q. Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
Go to Step 2 .

STEP 2. Connector check: A-07 air flow sensor connector

Q. Is the check result normal?
Go to Step 3 .
Repair or replace the connector.

STEP 3. Perform voltage measurement at A-07 air flow sensor connector.

  • Disconnect connector, and measure at harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 3 and earth.
OK: System voltage

Q. Is the check result normal?
Go to Step 5 .
Go to Step 4 .

STEP 4. Connector check: A-37X engine control relay connector

Q. Is the check result normal?

    Check and repair harness between A-37X (terminal No. 2) engine control relay connector and A-07 (terminal No. 3) air flow sensor connector.

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

STEP 5. Perform resistance measurement at A-07 air flow sensor connector.

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

Q. Is the check result normal?
Go to Step 9 .
Go to Step 6 .

STEP 6. Connector check: B-10 engine-ECU connector

Q. Is the check result normal?
Go to Step 7 .
Repair or replace the connector.

STEP 7. Check harness between A-07 (terminal No. 2) air flow sensor connector and B-10 (terminal No. 155) engine-ECU connector.

  • Check earthing line for open circuit and damage.

Q. Is the check result normal?
Go to Step 8 .
Repair the damaged harness wire.

STEP 8. M.U.T.-III data list

  • Refer to Data List Reference Table .

  1. Item 114: Air flow sensor

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

STEP 9. Connector check: A-37X engine control relay connector

Q. Is the check result normal?
Go to Step 10 .
Repair or replace the connector.

STEP 10. Check harness between A-37X (terminal No. 2) engine control relay connector and A-07 (terminal No. 3) air flow sensor connector.

  • Check power supply line for damage.

Q. Is the check result normal?
Go to Step 11 .
Repair the damaged harness wire.

STEP 11. Connector check: B-10 engine-ECU connector

Q. Is the check result normal?
Go to Step 12 .
Repair or replace the connector.

STEP 12. Check harness between A-07 (terminal No. 1) air flow sensor connector and B-10 (terminal No. 140) 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. Is the check result normal?
Check end.
Replace the engine-ECU.