Oxygen Sensor Monitor

WARNING: This page is about a different car, the 2003 Dodge Dakota. However, it is still accessible from the selected car via links, so may be relevant.

Effective control of exhaust emissions is achieved by an oxygen feedback system. The most important element of the feedback system is the Oxygen (O2) sensor. The O2 sensor is located in the exhaust path. Once it reaches operating temperature 572-662°F, the sensor generates a voltage that is inversely proportional to the amount of oxygen in the exhaust. The information obtained by the sensor is used to calculate the fuel injector pulse width. This maintains a 14.7:1 air/fuel ratio. At this mixture ratio, the catalyst works best to remove Hydrocarbons (HC), Carbon Monoxide (CO) and Nitrogen Oxide (NOx) from the exhaust.

The O2 sensor is also the main sensing element for the Catalyst and Fuel Monitors. The O2 sensor can fail in any or all of the following manners.

Slow Response Rate
Reduced Output Voltage
Dynamic Shift
Shorted Or Open Circuits

Response rate is the time required for the sensor to switch from lean to rich once it is exposed to a richer than optimum air/fuel mixture or vice versa. As the sensor starts malfunctioning, it could take longer to detect the changes in the oxygen content of the exhaust gas. The output voltage of the O2 sensor ranges from 0 to 1 volt. A good sensor can easily generate any output voltage in this range as it is exposed to different concentrations of oxygen. To detect a shift in the air/fuel mixture (lean or rich), the output voltage has to change beyond a threshold value. A malfunctioning sensor could have difficulty changing beyond the threshold value.