O2S Stays Below Center (Lean)

NAME OF CODE:
O2S Stays Below Center (Lean)

WHEN MONITORED:
With the engine running in closed loop and the coolant temperature above 170°F.

SET CONDITION:
The oxygen sensor signal voltage stays below 0.5 without toggling for at least 8 minutes.

THEORY OF OPERATION:
The oxygen sensor is a voltage generating device. The PCM receives exhaust gas information from the O2 sensor. The sensor detects exhaust gas content by a galvanic reation 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 signal is controlling the air/fuel ratio.

Variations in the signals from the O2 sensor serve as air/fuel ratio indicators. Changes in the sensor signal occur because the air/fuel ratio is constantly changing.
- When the 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.

POSSIBLE CAUSES:
- Low fuel pressure
- Vacuum Leak
- Other engine sensor calibrations
- Ignition system failure
- O2 sensor failure
- Mechanical engine problem