General Information

Engine Control
P2251 HO2S Reference Ground Circuit/Open (Bank 1 / Sensor 1) - General Information

Component Location





General Description

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 PCM monitors this signal and determines whether the air/fuel mixture is rich or lean. The PCM 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.

DTC Description

The PCM monitors front O2 sensor signal level during fuel cut-off operation. This signal monitoring will determine open circuit of Reference Ground Circuit (PCM pin No. 53). The PCM sets DTC P2251 if front O2 signal during fuel cut-off is higher than predetermined threshold. If the same error code is set in the next driving cycle, the PCM illuminates the MIL

DTC Detecting Condition





Schematic Diagram





Signal Waveform