General Information

Engine Control
P2251 O2 Sensor Reference Ground Circuit/Open (Bank 1 Sensor 1) - General Information

Component Location





General Description

Lambda sensor installed at exhaust manifold is planar ZrO2 dual cell type and it senses O2 density of exhaust gas for accurate EGR control through fuel correction. It also limits smoke which is generated by reach air-fuel mixture at engine maximum loading condition. ECM controls pumping current in order to fit lamda-value from linear O2 sensor to 1.0.
Lean air-fuel mixture(1.0Rich air-fuel mixture(0.9This performance is the most active and fast at normal operating temp.(450°C~600°C) thus, in order to reach normal operating temp. and last at that temp., heater(heating coil) is integrated with Lambda sensor.
Heater coil is controlled by ECM as PWM. the resistance of heater coil is low when coil is cold thus, current through it increases while resistance is high when coil is hot thus, current decreases. With this principle, Lambda sensor temp. is measured and Lambda sensor heater operation varies based on the data.

DTC Description

ECM assumes the ground circuit is open and shows P2251 when upstream O2 sensor is 1.49 - 1.53V and internal resistance gets high.

DTC Detecting Condition

Diagnostic Circuit Diagram

Signal Waveform & Data

Waveform of sensor Current Pump at IG KEY "ON" and Engine running. It fluctuates between 2V and 3V periodically.
Waveform of sensor Vertual Ground Output at IG KEY "ON" and Engine running. 2.5V is displayed.
Waveform of sensor Current Adjust at IG KEY "ON" and Engine running. It fluctuates between 2V and 3V periodically. Waveform of sensor Nernst Voltage at IG KEY "ON" and Engine running. 2.9V is displayed.