P0131

DTC P0131: Heated Oxygen Sensor Circuit Low Voltage (bank 1, sensor 1)

Right Bank Heated Oxygen Sensor (Front) Circuit Part 1:

Right Bank Heated Oxygen Sensor (Front) Circuit Part 2:

CIRCUIT OPERATION
- A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the PCM (terminal No. 92) from the output terminal (terminal No. 4) of the right bank heated oxygen sensor (front).
- Terminal No. 2 of the right bank heated oxygen sensor (front) is grounded with PCM (terminal No. 69).

TECHNICAL DESCRIPTION
- The right bank heated oxygen sensor (front) detects the concentration of oxygen in the exhaust gas; it converts those data to voltage, and inputs the resulting signals to the PCM.
- When the right bank heated oxygen sensor (front) begins to deteriorate, the heated oxygen sensor signal response becomes poor.
- The PCM forcibly varies the air/fuel mixture to make it leaner and richer, and checks the response speed of the right bank heated oxygen sensor (front) In addition, the PCM also checks for an open circuit in the right bank heated oxygen sensor (front) output line.

DESCRIPTIONS OF MONITOR METHODS
Right bank heated oxygen sensor (front) output voltage stays low when air/fuel ratio is forced to be rich The above procedure is repeated when oxygen sensor is inactive

MONITOR EXECUTION
Continuous

MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

Other Monitor (There is no temporary DTC stored in memory for the item monitored below)
- Heated oxygen sensor heater (front) monitor.
- Misfire monitor.
- Fuel system monitor.

Sensor (The sensor below is determined to be normal)
- Mass airflow sensor.
- Engine coolant temperature sensor.
- Intake air temperature sensor.
- Barometric pressure sensor.
- Throttle position sensor.
- Accelerator pedal position sensor.

DTC SET CONDITIONS

Logic Flow Chart:

Logic Flow Chart

Check Conditions
- 3 minutes or more have passed since the engine starting sequence was completed
- Right bank heated oxygen sensor (front) signal voltage has continued to be 0.2 volt or lower.
- Engine coolant temperature is higher than 76 °C (169 °F).
- Engine speed is higher than 1,200 r/min
- Volumetric efficiency is higher than 25 percent.
- Mass airflow sensor output is 8 g/sec or more.
- At least 20 seconds have passed since fuel shut off control was canceled.
- Monitoring time: 10 seconds.

Judgement Criteria
- Making the air/fuel ratio 15 percent richer for 10 seconds does not result in raising the heated oxygen sensor (front) output voltage beyond 0.2 volt

OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle - Procedure 6 - Other Monitor. OBD-II Drive Cycle Pattern Lists

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Right bank heated oxygen sensor (front) failed.
- Short circuit in right bank heated oxygen sensor (front) output line.
- Connector damage.
- PCM failed.

DIAGNOSIS

Required Special Tools:
- MB991958: Scan tool (MUT-III Sub Assembly)
- MB991824: V.C.I
- MB991827: USB Cable
- MB991910: Main Harness A

- MD998464: Test Harness




STEP 1. Using scan tool MB991958, check data list item 39: Heated Oxygen Sensor Bank 1, Sensor 1 (right front).

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.

1. Connect scan tool MB991958 to the data link connector.
2. Start the engine and run at idle.
3. Set scan tool MB991958 to the data reading mode for item 39, Heated Oxygen Sensor Bank 1, Sensor 1 (right front).
- Warm up the engine When the engine is revved, the output voltage should measure 0.6 to 1.0 volt.
- Warm up the engine When the engine is idling, the output voltage should repeat 0.4 volt and 0.6 to 1.0 volt alternately.

4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the sensor operating properly?

YES: It can be assumed that this malfunction is intermittent. Refer to How to Use Troubleshooting/Inspection Service Points.

NO: Go to Step 2.







STEP 2. Check the right bank heated oxygen sensor (front).

1. Disconnect the right bank heated oxygen sensor (front) connector B-09 and connect test harness special tool, MD998464, to the connector on the right bank heated oxygen sensor (front) side.
2. Warm up the engine until engine coolant temperature reaches 80 °C (176 °F) or higher.
3. Perform a tracing for 5 minutes or more with the engine speed of 4,500 r/min.
4. Connect a digital voltage meter between terminal No. 2 (black clip) and terminal No. 4 (white clip).
5. While repeatedly revving the engine, measure the right bank heated oxygen sensor (front) output voltage.

Standard value: 0.6 - 1.0 volt

CAUTION:
- Be very careful when connecting the jumper wire; incorrect connection can damage the oxygen sensor
- Be careful the heater is broken when voltage of beyond 8 V is applied to the oxygen sensor heater

NOTE: If the sufficiently high temperature (of approximate 400 °C or more) is not reached although the oxygen sensor is normal, the output voltage would be possibly low although the rich air-fuel ratio Therefore, if the output voltage is low, use a jumper wire to connect the terminal No. 1 (red clip of special tool) and the terminal No. 3 (blue clip of special tool) of the oxygen sensor with a (+) terminal and (-) terminal of 8 V power supply respectively, then check again.

Q: Is the voltage between 0.6 and 1.0 volt?

YES: Go to Step 3.

NO: Replace the right bank heated oxygen sensor (front). Then go to Step 5.







STEP 3. Check harness connector B-09 at right bank heated oxygen sensor (front) and connector B-22 at PCM for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 4.

NO: Repair or replace it. Refer to Harness Connector Inspection. Then go to Step 5.







STEP 4. Check for short circuit to ground between right bank heated oxygen sensor (front) connector B-09 (terminal No. 4) and PCM connector B-22 (terminal No. 92).

Q: Is the harness wire in good condition?

YES: Replace the PCM. Then go to Step 5.

NO: Repair it. Then go to Step 5.

STEP 5. Test the OBD-II drive cycle.

1. Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Procedure 6 - Other Monitor. OBD-II Drive Cycle Pattern Lists
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0131 set?

YES: Retry the troubleshooting.

NO: The inspection is complete.