O2S Stays Above Center (Rich)

WHEN MONITORED
With the engine running in closed loop and not at wide open throttle.

SET CONDITION
The oxygen sensor 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 each generate a varying voltage signal dependent upon exhaust gas oxygen content at that point in the exhaust.

- Oxygen sensor voltage signals are produced through a galvanic reaction within the sensors.

Using the oxygen sensor voltage signals as air/fuel ratio indicators the PCM can tell how well the system is responding to its output signals.

- 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 approximately 1 volt.

- When oxygen content is high (lean mixture), the voltage signal will be low, approximately 0.1 volt.

PROBABLE CAUSES
- High fuel pressure
- Other engine sensor calibrations
- Ignition system failure
- Oxygen sensor failure
- Mechanical engine problem