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DTC P2251: Linear Air-Fuel Ratio Sensor Negative Current Control Circuit/Open
 
 
 
 
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 connector terminal and the ECM terminal LPFL detects the air-fuel ratio.
  • The auxiliary line between the linear air-fuel ratio sensor connector terminal and the ECM terminal LSFL detects the air-fuel ratio.
  • The line between the linear air-fuel ratio sensor connector terminal 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
  • The linear air-fuel ratio sensor heater or the exhaust gas heats the linear air-fuel ratio sensor to sufficiently activate the linear air-fuel ratio sensor, resulting in the small resistance. However, the DTC is stored as an open circuit if the large resistance continues.
 
 
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 60 - 308 seconds have passed since the engine starting sequence was completed.
Judgment Criteria
  • The sensor impedance is be higher than 450 ohms for 2 seconds.
  • The reference circuit voltage is be lower than 5.3 volts for 2 seconds.
 
 
FAIL-SAFE AND BACKUP FUNCTION
  • Does not control air-fuel ratio closed loop.
  • Control linear air-fuel ratio sensor heater off.
 
 
OBD-II DRIVE CYCLE PATTERN
  • Refer to Diagnosis Function - OBD-II Drive Cycle - Pattern 21 .
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be stored are:)
  • Linear air-fuel ratio sensor failed.
  • Open 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 open circuit in LEFL 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 4.
 
STEP 2. 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 21 .
(4) Check the diagnostic trouble code (DTC).
Is DTC P2251 stored?
Then go to Step 3.
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 3. 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 21 .
(3) Check the diagnostic trouble code (DTC).
Is DTC P2251 stored?
Replace the ECM (Refer to, Removal and Installation ). Then go to Step 4.
The inspection is complete.
 
STEP 4. 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 21 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P2251 stored?
Retry the troubleshooting.
The inspection is complete.