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DTC P0131: Linear Air-Fuel Ratio Sensor Circuit Low Voltage
 
 
 
 
CIRCUIT OPERATION
The linear air-fuel ratio sensor and the ECM are connected by the following three lines to detect the air-fuel ratio.
  • The line between the linear air-fuel ratio sensor and the ECM terminal LPFL detects the air-fuel ratio.
  • The auxiliary line between the linear air-fuel ratio sensor and the ECM terminal LSFL detects the air-fuel ratio.
  • The line between the linear air-fuel ratio sensor and the ECM terminal LEFL is connected to ground.
 
 
TECHNICAL DESCRIPTION
  • The ECM effects air/fuel ratio feedback control in accordance with the signals from the linear air-fuel ratio sensor.
  • If the linear air-fuel ratio sensor has deteriorated, corrections will be made by the heated oxygen sensor (rear).
 
 
DESCRIPTIONS OF MONITOR METHODS
  • If one of the three line voltages is excessively low or if all the three line voltages are excessively low, the DTC is stored as a malfunction.
 
 
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)
  • Linear air-fuel ratio sensor heater 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
 
 
Check Conditions
  • Battery positive voltage is between 10 and 16.5 volts.
  • More than 40 seconds have passed since the engine starting sequence was completed.
Judgment Criterion
  • The pumping circuit voltage is be lower than 2 volts for 2 seconds.
or
  • The reference circuit voltage is be lower than 1.2 volt for 2 seconds.
or
  • The negative circuit voltage is be lower than 1.2 volt for 2 seconds.
 
 
FAIL-SAFE AND BACKUP FUNCTION
  • Does not control air-fuel ratio closed loop.
 
 
OBD-II DRIVE CYCLE PATTERN
  • Refer to Diagnosis Function - OBD-II Drive Cycle - Pattern 22 .
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be stored are: )
  • Linear air-fuel ratio sensor failed.
  • Shorted linear air-fuel ratio sensor circuit, or connector damage.
  • ECM failed.

 
 
DIAGNOSIS
Required Special Tools:
  • MB992744: Vehicle Communication Interface-Lite (V.C.I.-Lite)
  • MB992745: V.C.I.-Lite Main Harness A
  • MB992747: V.C.I.-Lite USB Cable Short
  • MB992748: V.C.I.-Lite USB Cable Long
  • MB991958: Scan Tool (M.U.T.-III Sub Assembly)
    • MB991824: Vehicles Communication Interface (V.C.I.)
    • MB991827: M.U.T.-III USB Cable
    • MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)
STEP 1. Check of short circuit to ground in LSFL line between linear air-fuel ratio sensor connector and ECM connector.
Is the harness wire in good condition?
Go to Step 2.
Repair the connector(s) or wiring harness. Then go to Step 6.
 
STEP 2. Check of short circuit to ground in LPFL line between linear air-fuel ratio sensor connector and ECM connector.
Is the harness wire in good condition?
Go to Step 3.
Repair the connector(s) or wiring harness. Then go to Step 6.
 
STEP 3. Check of short circuit to ground in LEFL line between linear air-fuel ratio sensor connector and ECM connector.
Is the harness wire in good condition?
Go to Step 4.
Repair the connector(s) or wiring harness. Then go to Step 6.
 
STEP 4. Test the OBD-II drive cycle.
cautionTo prevent damage to scan tool (M.U.T.-III), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-III).
(1) Connect scan tool (M.U.T.-III). Refer to HOW TO CONNECT THE SCAN TOOL (M.U.T.-III) .
(2) Turn the ignition switch to the "ON" position and delete the DTC.
(3) Carry out the test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 22 .
(4) Check the diagnostic trouble code (DTC).
Is DTC P0131 stored?
Then go to Step 5.
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 .
 
STEP 5. Replace the linear air-fuel ratio sensor.
(1) Replace the linear air-fuel ratio sensor.
(2) Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 22 .
(3) Check the diagnostic trouble code (DTC).
Is DTC P0131 stored?
Replace the ECM (Refer to Removal and Installation ). Then go to Step 6.
The inspection is complete.
 
STEP 6. 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 22 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P0131 stored?
Retry the troubleshooting.
The inspection is complete.