Left or Right O2S Stays Above Center (Rich)
NAME OF CODELeft or Right 02S Stays Above Center (Rich)
WHEN MONITORED
With the engine running in closed loop and not at wide open throttle.
SET CONDITION
The oxygen sensor (O2) signal voltage stays above 0.5 volts but less than 1.2 volts without toggling for at least 8 minutes.
THEORY OF OPERATION
The oxygen sensors are voltage generating devices. The Powertrain Control Module (PCM) receives exhaust gas information from the 02 sensors. The sensor(s) detect 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 sensors tell the PCM how well its output signals are controlling the air/fuel ratio. Variations in the signals from the 02 sensor(s) serve as air/fuel ratio indicators. Changes in the sensor signals occur because the air/fuel ratio is constantly changing. When oxygen content is low (rich mixture), the voltage signal will be high, approximately 1 volt. With a lean mixture (high oxygen content), the voltage signal will be low, approximately 0.1 volt.
POSSIBLE CAUSES
- Catalyst
- EGR system
- High fuel pressure
- Injectors
- Manifold Absolute Pressure (MAP) sensor
- O2 sensor failure
- Coolant temp sensor
- Evaporative emission system
- Mechanical engine problem
- Wiring harness/connectors