P0131
DTC P0131: Heated Oxygen Sensor Circuit Low VoltageHeated Oxygen Sensor (Front) Circuit Part 1:
Heated Oxygen Sensor (Front) Circuit Part 2:
CIRCUIT OPERATION
- A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the ECM (terminal No.71) from the output terminal (terminal No.4) of the heated oxygen sensor (front).
- Terminal No.2 of the heated oxygen sensor (front) is grounded with ECM (terminal No.49).
TECHNICAL DESCRIPTION
- The heated oxygen sensor (front) detects the concentration of oxygen in the exhaust gas; it converts this data to voltage, and inputs the resulting signals to the ECM.
- When the heated oxygen sensor (front) begins to deteriorate, the heated oxygen sensor signal response becomes poor.
- The ECM forcibly varies the air/fuel mixture to make it leaner and richer, and checks the response speed of the heated oxygen sensor (front). In addition, the ECM also checks for an open circuit in the heated oxygen sensor (front) output line.
DESCRIPTIONS OF MONITOR METHODS
- 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)
- Volume airflow sensor
- Engine coolant temperature sensor
- Intake air temperature sensor
- Barometric pressure sensor
- Throttle position sensor
- Accelerator position sensor
DTC SET CONDITIONS
Logic Flow Chart:
Logic Flow Chart
Check Conditions
- After 2 seconds or more pass from the time when the monitor determines normally for detecting an open circuit.
- Heated oxygen sensor (front) signal voltage has continued to be 0.2 volt or lower.
- Engine coolant temperature is higher than 76 degrees C (169 degrees F).
- Volume airflow sensor output frequency is 56 Hz or more.
- At least 20 seconds have passed since fuel shut off control was canceled.
- Monitoring time: 8 seconds.
Judgment Criterion
- Making the air/fuel ratio 15 percent for 8 seconds richer 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 - Pattern 11. OBD-II Drive Cycle Pattern Lists
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Heated oxygen sensor (front) deteriorated.
- Short circuit in heated oxygen sensor (front) output line.
- Connector damage.
- ECM failed.
DIAGNOSIS
Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991911: Main Harness B
- MD998464: Test Harness
STEP 1. Using scan tool MB991958, check data list item 11: Heated Oxygen Sensor (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 11, Heated Oxygen Sensor (front).
- Warm up the engine. When the engine is revved, the output voltage should be 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.
NO: Go to Step 2.
STEP 2. Check the heated oxygen sensor (front).
1. Disconnect the heated oxygen sensor (front) connector B-113 and connect test harness special tool, MD998464, to the connector on the heated oxygen sensor (front) side.
2. Warm up the engine until engine coolant temperature reaches 80 degrees C (176 degrees F) or higher.
3. Perform a racing 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 heated oxygen sensor (front) output voltage.
Standard value: 0.6 - 1.0 volt
CAUTION:
- Be very careful when connecting the jumper wires; incorrect connection can damage the heated oxygen sensor.
- Be careful the heater is broken when voltage of beyond 8 volts is applied to the heated oxygen sensor heater.
NOTE: If the sufficiently high temperature [of approximate 400 degrees C (752 degrees F) or more] is not reached although the heated 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) and the terminal No.3 (blue clip) of the heated oxygen sensor with the positive terminal and the negative terminal of 8 volts power supply respectively, then check again.
Q: Is the measured voltage between 0.6 and 1.0 volt?
YES: Go to Step 3.
NO: Replace the heated oxygen sensor (front). Then go to Step 5.
STEP 3. Check harness connector B-113 at heated oxygen sensor (front) and connector C-117 at ECM for damage.
Q: Is the harness connector in good condition?
YES: Go to Step 4.
NO: Repair or replace it. Then go to Step 5.
STEP 4. Check for short circuit to ground between heated oxygen sensor (front) connector B-113 (terminal No.4) and ECM connector C-117 (terminal No.71).
Q: Is the harness wire in good condition?
YES: Replace the ECM. 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 - Pattern 11. 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.