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. 3).
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. 4).

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 more than 11 V and is less than 16.5 V.

Judgement Criterion

The right bank oxygen sensor (front) heater current is less 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 more than 11 V and is less than 16.5 V.

Judgement Criterion

The right bank oxygen sensor (front) heater voltage is less than 2.0 V for 2 seconds.

FAIL-SAFE AND BACKUP FUNCTION

None

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: A-140 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 A-140 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 A-140 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-20X engine control relay connector

Q. Is the check result normal?

	Check and repair harness between A-140 (terminal No. 1) right bank oxygen sensor (front) connector and A-20X (terminal No. 3) engine control relay connector. Check power supply line for open/short circuit.

	Repair or replace the connector.

STEP 5. Connector check: C-169 engine-ECU connector

Q. Is the check result normal?

	Go to Step 6 .

	Repair or replace the connector.

STEP 6. Perform voltage measurement at C-169 engine-ECU connector.

Disconnect connector, and measure at harness side.
Ignition switch: ON
Voltage between terminal No. 4 and earth.

OK: System voltage

Q. Is the check result normal?

	Go to Step 7 .

	Check and repair harness between A-140 (terminal No. 3) right bank oxygen sensor (front) connector and C-169 (terminal No. 4) engine-ECU connector. Check earthing line for open/short circuit.

STEP 7. Check harness between A-140 (terminal No. 3) right bank oxygen sensor (front) connector and C-169 (terminal No. 4) engine-ECU connector.

Check earthing line for damage.

Q. Is the check result normal?

	Go to Step 8 .

	Repair the damaged harness wire.

STEP 8. Connector check: A-20X engine control relay connector

Q. Is the check result normal?

	Go to Step 9 .

	Repair or replace the connector.

STEP 9. Check harness between A-140 (terminal No. 1) right bank oxygen sensor (front) connector and A-20X (terminal No. 3) engine control relay connector.

Check power supply line for damage.

Q. Is the check result normal?

	Go to Step 10 .

	Repair the damaged harness wire.

STEP 10. M.U.T.-III diagnosis code

Reconfirmation of diagnosis code.

Q. Is the 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 ).