Code No. P0131: Oxygen Sensor Circuit Low Voltage <Vehicles with catalytic converter>

OPERATION

The sensor signal is inputted to the engine-ECU <M/T> or engine-A/T-ECU <A/T> (terminal No. 108) from the oxygen sensor output terminal (terminal No. 4).
The oxygen sensor (terminal No. 2) is earthed with engine-ECU <M/T> or engine-A/T-ECU <A/T> (terminal No. 96).

FUNCTION

The oxygen sensor converts the concentration of oxygen in the exhaust emission into a voltage and inputs the signal to the engine-ECU <M/T> or engine-A/T-ECU <A/T>.
When the air-fuel ratio is richer than the theoretical air-fuel ratio, the oxygen sensor 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 <M/T> or engine-A/T-ECU <A/T> controls the fuel injection amount so that the air-fuel ratio can be equivalent to the theoretical air-fuel ratio.

TROUBLE JUDGMENT

Check Conditions

DTC No. P0130 and P0132 are not shown.
The engine coolant temperature is approximately 76°C or more.

Judgment Criterion

Oxygen sensor output voltage is 0.2 V or less.

PROBABLE CAUSES

Failed oxygen sensor
Short circuit in oxygen sensor circuit or loose connector contact
Failed engine-ECU <M/T> or engine-A/T-ECU <A/T>

DIAGNOSIS PROCEDURE

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

Refer to Data List Reference Table .

Item AC: Oxygen sensor

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: C-21 oxygen sensor connector

Q. Is the check result normal?

	Go to Step 3 .

	Repair or replace the connector.

STEP 3. Perform resistance measurement at C-21 oxygen sensor 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: D-246 engine-ECU <M/T> connector or D-217 engine-A/T-ECU <A/T> connector

Q. Is the check result normal?

	Go to Step 5 .

	Repair or replace the connector.

STEP 5. Check harness between C-21 (terminal No. 2) oxygen sensor connector and D-246 (terminal No. 96) engine-ECU <M/T> connector or D-217 (terminal No. 96) engine-A/T-ECU <A/T> connector.

note

Before checking harness, check intermediate connectors D-111 and D-225, and repair if necessary.

Check earthing line for 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 AC: Oxygen sensor

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 <M/T> or engine-A/T-ECU <A/T>.

STEP 7. Perform voltage measurement at C-21 oxygen sensor connector.

Use special tool test harness (MB991316) to connect connector, and measure at pick-up harness.
Engine: After warm-up
Transmission: Neutral <M/T> or P range <A/T>
Voltage between terminal No. 4 and earth.

OK:
When the engine is 2,500 r/min, 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 oxygen sensor itself.

Check oxygen sensor itself (Refer to ).

Q. Is the check result normal?

	Go to Step 9 .

	Replace oxygen sensor.

STEP 9. Connector check: D-246 engine-ECU <M/T> connector or D-217 engine-A/T-ECU <A/T> connector

Q. Is the check result normal?

	Check intermediate connector D-225, and repair if necessary. If intermediate connector is normal, check and repair harness between C-21 (terminal No. 4) oxygen sensor connector and D-246 (terminal No. 108) engine-ECU <M/T> connector or D-217 (terminal No. 108) engine-A/T-ECU <A/T> connector. Check output line for short circuit and damage.

	Repair or replace the connector.

STEP 10. Connector check: D-246 engine-ECU <M/T> connector or D-217 engine-A/T-ECU <A/T> connector

Q. Is the check result normal?

	Go to Step 6 .

	Repair or replace the connector.