O2/AFR Sensor

Category: automotive

A sensor that measures the amount of unburned oxygen in the exhaust to optimize the air-fuel mixture.

The sensor is the "exhaust critic." It tells the PCM if the engine is running "rich" (too much fuel) or "lean" (too little). If the sensor fails, the PCM guesses, leading to terrible fuel economy and, eventually, a clogged catalytic converter.

Common Examples

• A failing O2 sensor was sending faulty readings to the PCM, causing the engine to dump excess fuel into the exhaust stream.
• Upgrading to a wideband air-fuel ratio sensor is standard practice for any performance tuning to ensure a safe combustion mix.