The linear O2 sensor is mounted on the front side of the Catalytic Converter (warm-up catalytic converter) or in the front exhaust pipe. It detects a wide range of air/fuel ratios in the exhaust gas from the rich to lean regions. This linear O2 sensor produces a current that corresponds to a specific air/fuel ratio. The ECM monitors this signal and determines whether the air/fuel mixture is rich or lean. The ECM constantly monitors the linear O2 sensor and increases or decreases the fuel injection duration using this signal. This is called closed-loop fuel control operation.
The ECM monitors front O2 sensor reference ground circuit(VG) and sets DTC P2251 if front O2 sensor signal stuck is detected.
Item
Detecting Condition
Possible Cause
DTC Strategy
Reference ground circuit open (VG)
Poor connection or damaged harness
Open in HO2S control circuit
Front HO2S
Enable Conditions
11V < Battery voltage < 16V
Threshold Value
1.9V < Signal < 2.1V for 5sec during internal test
Symptom detected on no activity
Signal < 2.1V during fuel cut off
Diagnostic Time
Within 15sec. after related symptom detected.
Mil On Condition
2 Driving Cycles