Left or Right O2S Stays Below Center (Lean)
NAME OF CODELeft or Right 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 (O2) signal voltage stays below 0.5 volts without toggling for at least 8 minutes.
THEORY OF OPERATION
The oxygen sensor is a voltage generating device. The Powertrain Control Module (PCM) receives exhaust gas information from the 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 signal is controlling the air/fuel ratio. Variations in the signal 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 oxygen content is low (rich mixture), the voltage signal will be high, approximately 1 volt. When oxygen content is high (lean mixture), the voltage signal will be low, approximately 0.1 volt.
POSSIBLE CAUSES
- Ignition system failure
- Fuel pump/filter
- Injectors
- Low fuel pressure
- MAP sensor
- O2 sensor failure
- Vacuum leak
- Mechanical engine problem
- Wiring harness/connectors