Code No. P0131: Oxygen Sensor (front) Circuit Low Voltage




OPERATION




FUNCTION




TROUBLE JUDGMENT


Check Conditions
Judgement Criterion

FAIL-SAFE AND BACKUP FUNCTION




PROBABLE CAUSES




DIAGNOSIS PROCEDURE


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



  • Data list reference table (Refer to ).

  1. Item AC: Oxygen sensor (front)

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. Perform voltage measurement at oxygen sensor (front) connector.



  • Disconnect connector, and measure at harness side.
  • Ignition switch: "ON"
  • Voltage between terminal engine-ECU OFLE line and body earth.
OK: 0.4 - 0.6 V

Q. Is the check result normal?

Go to Step 5.
Go to Step 3.

STEP 3. Check harness between oxygen sensor (front) connector terminal and engine-ECU connector terminal OFLE.



  • Check earthing line for open/short circuit.

Q. Is the check result normal?

Go to Step 4.
Repair or replace the connector, or repair the damaged harness wire.

STEP 4. M.U.T.-III data list



  • Data list reference table (Refer to ).

  1. Item AC: Oxygen sensor (front)

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 5. Check harness between oxygen sensor (front) connector terminal and engine-ECU connector terminal OFLE.



  • 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. Perform voltage measurement at oxygen sensor (front) connector.



  • Use special tool test harness (MB991658) to connect connector, and measure at pick-up harness.
  • Engine: After warm-up
  • Transmission: Neutral <M/T> or P range <CVT>
  • Voltage between terminal engine-ECU O2FL line and earth.
OK:
    When the engine is 2,500 r/min, the output voltage should repeat 0.9 V or less <=> 1.1 to 1.5 V alternately.

Q. Is the check result normal?

Go to Step 8.
Go to Step 7.

STEP 7. Check oxygen sensor (front) itself.



  • Oxygen sensor (front) connector check.
  • Oxygen sensor check (Refer to ).

Q. Is the check result normal?


    Repair or replace the connector, or check and repair harness between oxygen sensor (front) connector terminal and engine-ECU connector terminal O2FL.

    • Check output line for short circuit.
Repair or replace the connector, or replace oxygen sensor (front).

STEP 8. Check harness between oxygen sensor (front) connector terminal and engine-ECU connector terminal O2FL.



  • Check output line for open circuit and damage.

Q. Is the check result normal?

Go to Step 4.
Repair or replace the connector, or repair the damaged harness wire.