Inspection Procedure 34: Air/Fuel Ratio Sensor (Lambda sensor) System <Vehicle with DPF>










OPERATION



  • Power is supplied to the heater power terminal (terminal No. 2) of the air/fuel ratio sensor connector from the engine control relay (terminal No. 2).
  • The heater (terminal No. 5) of the air/fuel ratio sensor connector is controlled by the power transistor in the engine-ECU (terminal No. 89).
  • The oxygen concentration signal is inputted to the engine-ECU (terminal No. 71) from the air/fuel ratio sensor output terminal (terminal No. 1).
  • The power voltage is earthed to the engine-ECU (terminal No. 136) from the air/fuel ratio sensor (terminal No. 3).
  • The pump current is inputted to the engine-ECU (terminal No. 114) from the air/fuel ratio sensor output terminal (terminal No. 6).
  • The Lambda value signal is inputted to the engine-ECU (terminal No. 92) from the air/fuel ratio sensor output terminal (terminal No. 4).

FUNCTION



  • The air/fuel ratio sensor is used to detect the oxygen concentration in the exhaust gas.
  • The engine-ECU calculates the quantity and start of extended injection based on this output signal.
  • Air/fuel ratio sensor heater control the current applied to the air/fuel ratio sensor heater circuit in accordance with signals from the engine-ECU.

PROBABLE CAUSES



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

DIAGNOSIS PROCEDURE

STEP 1. Connector check: B-124 air/fuel ratio sensor connector

Q. Is the check result normal?
Go to Step 2 .
Repair or replace the connector.

STEP 2. Perform voltage measurement at B-124 air/fuel ratio sensor connector.

  • Disconnect connector, and measure at 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: A-33X engine control relay connector

Q. Is the check result normal?

    Check intermediate connector A-11 repair if necessary. If intermediate connector is normal, check and repair harness between B-124 (terminal No. 2) air/fuel ratio sensor connector and A-33X (terminal No. 2) engine control relay connector.

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

STEP 4. Perform voltage measurement at B-28 engine-ECU connector.

  • Disconnect connector, and measure at harness side.
  • Using a jumper wire, connect terminal No. 131 to earth.
  • Ignition switch: ON
  • Voltage between terminal No. 89 and earth.
OK: System voltage

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 intermediate connector A-10, and repair if necessary. If intermediate connector is normal, check and repair harness between B-124 (terminal No. 5) air/fuel ratio sensor connector and B-28 (terminal No. 89) engine-ECU connector

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

STEP 6. Connector check: B-28 engine-ECU connector

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

STEP 7. Check harness between B-124 (terminal No. 2) air/fuel ratio sensor connector and A-33X (terminal No. 2) engine control relay connector.
note Before checking harness, check intermediate connector A-11, and repair if necessary.

  • Check power supply line for damage.

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

STEP 8. Check harness between B-124 (terminal No. 5) air/fuel ratio sensor connector and B-28 (terminal No. 89) engine-ECU connector.
note Before checking harness, check intermediate connector A-10, and repair if necessary.

  • Check earthing line for damage.

Q. Is the check result normal?
Go to Step 9 .
Repair the damaged harness wire.

STEP 9. Check harness between B-124 (terminal No.3) air/fuel ratio sensor connector and B-28 (terminal No. 136) engine-ECU connector.
note Before checking harness, check intermediate connector A-10, and repair if necessary.

  • Check earthing line for open circuit and damage.

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

STEP 10. Check harness between B-124 (terminal No. 1) air/fuel ratio sensor connector and B-28 (terminal No. 71) engine-ECU connector.
note Before checking harness, check intermediate connector A-10, and repair if necessary.

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

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

STEP 11. Check harness between B-124 (terminal No. 4) air/fuel ratio sensor connector and B-28 (terminal No. 92) engine-ECU connector.
note Before checking harness, check intermediate connector A-10, and repair if necessary.

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

Q. Is the check result normal?
Go to Step 12 .
Repair the damaged harness wire.

STEP 12. Check harness between B-124 (terminal No. 6) air/fuel ratio sensor connector and B-28 (terminal No. 114) engine-ECU connector.
note Before checking harness, check intermediate connector A-10, and repair if necessary.

  • 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/fuel ratio sensor.

  • After replacing the air/fuel ratio sensor, re-check the trouble symptoms.

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