O2S Stays at Center

WHEN MONITORED
With the engine running for more than 2 minutes and engine temperature greater than 170°F.

SET CONDITION
The oxygen sensor signal voltage is 0.5 volts for 1.5 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
- Sensor output wire open
- Oxygen sensor failure