DTC P0131: Heated Oxygen Sensor (front) Circuit Low Voltage

CIRCUIT OPERATION

• A voltage corresponding to the oxygen concentration in the exhaust gas is sent to the ECM (terminal No. 38) from the output terminal (terminal No. 3) of the heated oxygen sensor (front).
  
• Terminal No. 4 of the heated oxygen sensor (front) is grounded with ECM (terminal No. 39).
  
• The ECM applies an offset voltage of 0.5 volt to terminal No. 4 of the heated oxygen sensor (front).
  

TECHNICAL DESCRIPTION

• The 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 ECM.
  
• When the heated oxygen sensor (front) begins to deteriorate, the heated oxygen sensor signal response becomes poor.
  
• The ECM checks for the heated oxygen sensor (front) output voltage.
  

DESCRIPTIONS OF MONITOR METHODS

Heated oxygen sensor (front) output voltage is under the specified range.

MONITOR EXECUTION

Continuous

MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

• Heated oxygen sensor (front) heater monitor
  
• Misfire monitor
  
• Fuel system monitor
  

• Mass airflow sensor
  
• Engine coolant temperature sensor
  
• Intake air temperature sensor
  
• Barometric pressure sensor
  
• Throttle position sensor
  
• Accelerator pedal position sensor
  

DTC SET CONDITIONS

• Heated oxygen sensor offset voltage is between 0.4 and 0.6 volt.
  
• Battery positive voltage is between 11 and 16.5 volts.
  
• More than 60 seconds have passed since the engine starting sequence was completed.
  

• Heated oxygen sensor (front) output voltage is less than 0.2 volt for 2 seconds.
  

FAIL-SAFE AND BACKUP FUNCTION

• None
  

OBD-II DRIVE CYCLE PATTERN

Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 22 .

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)

• Heated oxygen sensor (front) failed.
  
• Open or shorted circuit in heated oxygen sensor (front) output line, or harness damage.
  
• Open circuit in heated oxygen sensor (front) ground line, or harness damage.
  
• Connector damage.
  
• ECM failed.
  

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 AC, 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 or less and 0.6 to 1.0 volt alternately. (4)Turn the ignition switch to the "LOCK" (OFF) position. Q. Is the sensor operating properly? It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions . Go to Step 2.

(3)Measure the voltage between terminal No. 3 and ground by backprobing. Warm up the engine. When the engine is 2,500 r/min, the output voltage should repeat 0.4 volt or less and 0.6 to 1.0 volt alternately. (4)Turn the ignition switch to the "LOCK" (OFF) position. Q. Is the measured voltage within the specified range? Go to Step 3. Go to Step 8.

	Go to Step 4.

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 14.

(1)Disconnect all ECM connectors. Connect the power plant ECU check harness special tool MB992110 between the separated connectors. (2)Start the engine and run at idle.

(3)Measure the voltage between terminal No. 38 and ground. Warm up the engine. When the engine is 2,500 r/min, the output voltage should repeat 0.4 volt or less and 0.6 to 1.0 volt alternately. (4)Turn the ignition switch to the "LOCK" (OFF) position. Q. Is the measured voltage within the specified range? Go to Step 5. Go to Step 7.

	Go to Step 6.

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 14.

	It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions .

	Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP 42B, Diagnosis - ID Code Registration Necessity Judgment Table <Vehicles with KOS> or GROUP 42C, Diagnosis - ID Codes Registration Judgment Table <Vehicles with WCM> . Then go to Step 14.

	Check harness connector A-54 at intermediate connector for damage, and repair or replace as required. Refer to GROUP 00E, Harness Connector Inspection . If intermediate connector is in good condition, repair harness wire between heated oxygen sensor (front) connector C-44 (terminal No. 3) and ECM connector B-108 (terminal No. 38) because of open circuit or harness damage. Then go to Step 14.

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 14.

	Go to Step 9.

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 14.

	Go to Step 10.

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 14.

(1)Disconnect all ECM connectors. Connect the power plant ECU check harness special tool MB992110 between the separated connectors. (2)Turn the ignition switch to the "ON" position.

(3)Measure the voltage between terminal No. 39 and ground. Voltage should be between 0.4 and 0.6 volt. (4)Turn the ignition switch to the "LOCK" (OFF) position. Q. Is the measured voltage between 0.4 and 0.6 volt? Go to Step 11. Check harness connector A-54 at intermediate connector for damage, and repair or replace as required. Refer to GROUP 00E, Harness Connector Inspection . If intermediate connector is in good condition, repair harness wire between heated oxygen sensor (front) connector C-44 (terminal No. 4) and ECM connector B-108 (terminal No. 39) because of short circuit to ground. Then go to Step 14.

note Check harness after checking intermediate connector A-54. If intermediate connector is damaged, repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 14.

	Go to Step 12.

	Repair it. Then go to Step 14.

note Check harness after checking intermediate connector A-54. If intermediate connector is damaged, repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 14.

	Go to Step 13.

	Repair it. Then go to Step 14.

(4)Connect a digital voltage meter between terminal No. 3 and terminal No. 4. (5)While repeatedly revving the engine, measure the heated oxygen sensor (front) output voltage. (6)Standard value: 0.6 - 1.0 V caution Be very careful when connecting the jumper wires; incorrect connection can damage the heated oxygen sensor. Be careful the heater can be damaged if a voltage beyond 8 volts is applied to the heated oxygen sensor heater. note If the temperature of sensing area does not reach the high temperature [of approximately 400°C (752°F) or more] even though the heated oxygen sensor is normal, the output voltage would be possibly low in spite of the rich air/fuel ratio. Therefore, if the output voltage is low, use a jumper wire to connect the terminal No. 1 and the terminal No. 2 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? Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP 42B, Diagnosis - ID Code Registration Necessity Judgment Table <Vehicles with KOS> or GROUP 42C, Diagnosis - ID Codes Registration Judgment Table <Vehicles with WCM> . Then go to Step 14. Replace the heated oxygen sensor (front). Then go to Step 14.

(1)Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 22 .

	Retry the troubleshooting.

	The inspection is complete.