Code No. P0031: Linear A/F Sensor Heater Circuit Low Input




OPERATION




FUNCTION




TROUBLE JUDGEMENT


Check Conditions
Judgement Criterion
Check Conditions
Judgement Criterion

FAIL-SAFE AND BACKUP FUNCTION




PROBABLE CAUSES




DIAGNOSIS PROCEDURE


STEP 1. Check linear A/F sensor itself.



  • Linear A/F sensor connector check.
  • Linear A/F sensor check (Refer to ).

Q. Is the check result normal?

Go to Step 2.
Repair or replace the connector, or replace the linear A/F sensor.

STEP 2. Perform voltage measurement at linear A/F sensor connector.



  • Disconnect connector, and measure at harness side.
  • Power supply mode of electric motor switch: ACC
  • Voltage between terminal power supply line and body earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 3.

    Repair or replace the connector, or check and repair harness between linear A/F sensor connector terminal and engine control relay connector terminal.

    • Check power supply line for open/short circuit.

STEP 3. Perform voltage measurement at engine-ECU connector.



  • Disconnect engine-ECU harness, and connect special tool power plant ECU check harness (MB992110) to measure at connector for inspection.
  • Power supply mode of electric motor switch: ACC
  • Voltage between terminal LHFL and body earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 4.

    Repair or replace the connector, or check and repair harness between linear A/F sensor connector terminal and engine-ECU connector terminal LHFL.

    • Check earthing line for open/short circuit.

STEP 4. Check harness between linear A/F sensor connector terminal and engine control relay connector terminal.



  • Check power supply line for damage.

Q. Is the check result normal?

Go to Step 5.
Repair or replace the connector, or repair the damaged harness wire.

STEP 5. Check harness between linear A/F sensor connector terminal and engine-ECU connector terminal LHFL.



  • Check earthing line for damage.

Q. Is the check result normal?

Go to Step 6.
Repair or replace the connector, or repair the damaged harness wire.

STEP 6. M.U.T.-III diagnosis code



  • Reconfirmation of diagnosis code.

Q. Is diagnosis code stored?

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