Code No. P0031: Right Bank Oxygen Sensor (front) Heater Circuit Low Input












OPERATION



  • Power is supplied to the heater power terminal (terminal No. 1) of the right bank oxygen sensor (front) connector from the engine control relay (terminal No. 2).
  • The heater (terminal No. 3) of the right bank oxygen sensor (front) connector is controlled by the power transistor in the engine-ECU (terminal No. 33).

FUNCTION



  • The power supply to the right bank oxygen sensor (front) heater is controlled by the ON/OFF control of the power transistor in the engine-ECU.
  • Heating the right bank oxygen sensor (front) heater enables the right bank oxygen sensor (front) to provide good response even when the exhaust emission temperature is low.

TROUBLE JUDGEMENT


Check Conditions
  • More than 2 seconds have passed since the engine starting sequence was completed.
  • While the right bank oxygen sensor (front) heater is on.
  • Battery positive voltage is 11 - 16.5 V.
Judgement Criterion
  • The right bank oxygen sensor (front) heater current has continued to be lower than 0.17 A for 2 seconds.
Check Conditions
  • More than 2 seconds have passed since the engine starting sequence was completed.
  • While the right bank oxygen sensor (front) heater is off.
  • Battery positive voltage is 11 - 16.5 V.
Judgement Criterion
  • The right bank oxygen sensor (front) heater voltage has continued to be lower than 2.0 V for 2 seconds.

PROBABLE CAUSES



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

DIAGNOSIS PROCEDURE


STEP 1. Connector check: B-126 right bank oxygen sensor (front) connector


Q. Is the check result normal?

Go to Step 2 .
Repair or replace the connector.

STEP 2. Perform resistance measurement at B-126 right bank oxygen sensor (front) connector.



  • Disconnect connector, and measure at sensor side.
  • Resistance between terminal No. 1 and No. 3.
OK: 4.5 - 8.0 Ω (at 20°C)

Q. Is the check result normal?

Go to Step 3 .
Replace the right bank oxygen sensor (front).

STEP 3. Perform voltage measurement at B-126 right bank oxygen sensor (front) connector.



  • Disconnect connector, and measure at harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 1 and earth.
OK: System voltage

Q. Is the check result normal?

Go to Step 5 .
Go to Step 4 .

STEP 4. Connector check: A-33X engine control relay connector


Q. Is the check result normal?


    Check intermediate connector A-13, and repair if necessary. If intermediate connector is normal, check and repair harness between B-126 (terminal No. 1) right bank oxygen sensor (front) 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 5. Connector check: B-29 engine-ECU connector


Q. Is the check result normal?

Go to Step 6 .
Repair or replace the connector.

STEP 6. Check harness between B-126 (terminal No. 3) right bank oxygen sensor (front) connector and B-29 (terminal No. 33) engine-ECU connector.



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

Q. Is the check result normal?

Go to Step 7 .
Repair the damaged harness wire.

STEP 7. Check harness between B-126 (terminal No. 1) right bank oxygen sensor (front) connector and A-33X (terminal No. 2) engine control relay connector.


note Before checking harness, check intermediate connector A-13, 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. M.U.T.-III diagnosis code



  • Reconfirmation of diagnosis code.

Q. Is diagnosis code set?

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