Code No. P0131: Oxygen Sensor (front) Circuit Low Voltage <Except vehicles for Russia>


OPERATION



  • The sensor signal is inputted to the engine-ECU (terminal No. 38) from the oxygen sensor (front) output terminal (terminal No. 1).
  • The engine-ECU (terminal No. 39) applies an offset voltage of 0.5 V to the oxygen sensor (front) (terminal No. 2).

FUNCTION



  • The oxygen sensor (front) converts the concentration of oxygen in the exhaust emission into a voltage and inputs the signal to the engine-ECU.
  • When the air-fuel ratio is richer than the theoretical air-fuel ratio, the oxygen sensor (front) outputs a voltage of about 1 V. When it is leaner than the theoretical air-fuel ratio, it outputs a voltage of about 0 V.
  • In response to the signal, the engine-ECU controls the fuel injection amount so that the air-fuel ratio can be equivalent to the theoretical air-fuel ratio.

TROUBLE JUDGMENT


Check Conditions
  • More than 1 minute have passed since the engine starting sequence was completed.
  • Battery positive voltage is more than 11 V and is less than 16.5 V.
  • Oxygen sensor (front) offset voltage is more than 0.4 V and is less than 0.6 V.
Judgement Criterion
  • Oxygen sensor (front) output voltage is less than 0.2 V for 2 seconds.

FAIL-SAFE AND BACKUP FUNCTION



  • None

PROBABLE CAUSES



  • Failed oxygen sensor (front)
  • Open/short circuit or harness damage in oxygen sensor (front) circuit or loose connector contact
  • Failed engine-ECU

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. Connector check: B-32 oxygen sensor (front) connector

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

STEP 3. Perform voltage measurement at B-32 oxygen sensor (front) connector.

  • Disconnect connector, and measure at harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 2 and earth.
OK: 0.4 - 0.6 V

Q. Is the check result normal?
Go to Step 7.
Go to Step 4.

STEP 4. Connector check: B-26 engine-ECU connector

Q. Is the check result normal?
Go to Step 5.
Repair or replace the connector.

STEP 5. Check harness between B-32 (terminal No. 2) oxygen sensor (front) connector and B-26 (terminal No. 39) engine-ECU connector.

  • Check earthing line for open/short circuit.

Q. Is the check result normal?
Go to Step 6.
Repair the damaged harness wire.

STEP 6. 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 7. Connector check: B-26 engine-ECU connector

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

STEP 8. Check harness between B-32 (terminal No. 2) oxygen sensor (front) connector and B-26 (terminal No. 39) engine-ECU connector.

  • Check earthing line for damage.

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

STEP 9. Perform voltage measurement at B-32 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
  • Voltage between terminal No. 1 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 11.
Go to Step 10.

STEP 10. Check oxygen sensor (front) itself.



  • Oxygen sensor check (Refer to ).

Q. Is the check result normal?

    Check and repair harness between B-32 (terminal No. 1) oxygen sensor (front) connector and B-26 (terminal No. 38) engine-ECU connector.

    • Check output line for short circuit.
Replace oxygen sensor (front).

STEP 11. Check harness between B-32 (terminal No. 1) oxygen sensor (front) connector and B-26 (terminal No. 38) engine-ECU connector.

  • Check output line for open circuit and damage.

Q. Is the check result normal?
Go to Step 6.
Repair the damaged harness wire.