P0151 2/1 O2S Shorted to Ground

NAME OF CODE
O2S Voltage Shorted To Ground

WHEN MONITORED
With engine coolant temperature above 170°F on the previous key on, after a cold start, engine coolant below 98°F, and ambient/battery sensor reading within 27°F of engine coolant.

SET CONDITION
The oxygen sensor signal voltage is below 0.156 volts for 28 seconds after starting engine.

THEORY OF OPERATION
The oxygen sensor is a voltage generating device. The PCM receives exhaust gas information from bus O2 sensor. The sensor detects exhaust gas content by a galvanic reaction within the sensor that produces a voltage. After measuring the amount of oxygen in the exhaust gases, the oxygen sensor tells the PCM how well its output signals are controlling the air/fuel ratio. Variations in the signal from this O2 sensor serve as air/fuel ratio indicators. Changes in the sensor signal occur because the air/fuel ratio is constantly changing. When oxygen content is low (rich mixture), the voltage signal will be high, approximately 1.0 volt.

POSSIBLE CAUSES
- Sensor output wire shorted to ground
- Dirty/wet connection causing voltages tracking in connector
- O2 sensor failure
- Powertrain control module failure
- Connector terminals
- Connector wires