Code No. P0137: Right Bank Oxygen Sensor (rear) Circuit Low Voltage

OPERATION

The sensor signal is inputted to the engine-ECU (terminal No. 56) from the right bank oxygen sensor (rear) output terminal (terminal No. 4).
The right bank oxygen sensor (rear) (terminal No. 2) is earthed with engine-ECU (terminal No. 57).

FUNCTION

The right bank oxygen sensor (rear) 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 right bank oxygen sensor (rear) 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

Right bank oxygen sensor (rear) offset voltage is 0.4 - 0.6 V.
Battery positive voltage is 11 - 16.5 V.
3 minutes or more have passed since the engine starting sequence was completed.

Judgment Criterion

Right bank oxygen sensor (rear) output voltage is lower than 0.2 V for 2 seconds.

PROBABLE CAUSES

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

DIAGNOSIS PROCEDURE

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

Refer to Data List Reference Table .

Item AD: Right bank oxygen sensor (rear)

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-125 right bank oxygen sensor (rear) connector

Q. Is the check result normal?

	Go to Step 3 .

	Repair or replace the connector.

STEP 3. Perform resistance measurement at B-125 right bank oxygen sensor (rear) connector.

Disconnect connector, and measure at harness side.
Resistance between terminal No. 2 and earth.

OK: Continuity (2 Ω or less)

Q. Is the check result normal?

	Go to Step 7 .

	Go to Step 4 .

STEP 4. Connector check: B-29 engine-ECU connector

Q. Is the check result normal?

	Go to Step 5 .

	Repair or replace the connector.

STEP 5. Check harness between B-125 (terminal No. 2) right bank oxygen sensor (rear) connector and B-29 (terminal No. 57) engine-ECU connector.

Check earthing line for open circuit and damage.

Q. Is the check result normal?

	Go to Step 6 .

	Repair the damaged harness wire.

STEP 6. M.U.T.-III data list

Refer to Data List Reference Table .

Item AD: Right bank oxygen sensor (rear)

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. Perform voltage measurement at B-125 right bank oxygen sensor (rear) connector.

Use special tool test harness (MD998464) to connect connector, and measure at pick-up harness.
Transmission: 2nd range
Drive with wide open throttle.
Engine: 3,500 r/min or more
Voltage between terminal No. 4 and earth.

OK:
The output voltage should repeat 0 to 0.8 V alternately.

Q. Is the check result normal?

	Go to Step 10 .

	Go to Step 8 .

STEP 8. Check right bank oxygen sensor (rear) itself.

Check right bank oxygen sensor (rear) itself (Refer to ).

Q. Is the check result normal?

	Go to Step 9 .

	Replace the right bank oxygen sensor (rear).

STEP 9. Connector check: B-29 engine-ECU connector

Q. Is the check result normal?

	Check and repair harness between B-125 (terminal No. 4) right bank oxygen sensor (rear) connector and B-29 (terminal No. 56) engine-ECU connector. Check output line for short circuit and damage.

	Repair or replace the connector.

STEP 10. Connector check: B-29 engine-ECU connector

Q. Is the check result normal?

	Go to Step 11 .

	Repair or replace the connector.

STEP 11. Check harness between B-125 (terminal No. 4) right bank oxygen sensor (rear) connector and B-29 (terminal No. 56) engine-ECU connector.

Check output line for open circuit.

Q. Is the check result normal?

	Go to Step 6 .

	Repair the damaged harness wire.