Instead of giving a simple rich/lean indication, wide ratio air/fuel sensors measure the "actual" air/fuel ratio. A WRAF sensor can measure mixtures that range from extremely rich to extremely lean (even straight air!). This ability allows the PCM to control fuel mixtures much more precisely, to handle much leaner fuel mixtures, to reduce emissions and to improve fuel economy compared to ordinary switching O2 sensors. WRAF sensors react much faster than ordinary O2 sensors, which allows them to monitor the fuel mixture from individual cylinders as each puff of exhaust blows by the sensor element. The PCM can then adjust the mixture for each cylinder individually to reduce emissions and optimize fuel economy.

Car makers also like the new WRAF sensors because it allows the use of thinner catalyst coatings (platinum, palladium and rhodium) inside the catalytic converter. With the soaring price of precious metals lately, this can add up to significant cost savings for a vehicle manufacturer that produces millions of vehicles a year.

WRAF Operations
WRAF sensors don't generate a voltage signal like a common zirconia O2 sensor. An ordinary O2 sensor produces a voltage signal of 0.8 to 0.9 volts when the air/fuel mixture is rich, then drops to 0.3 volts or less when the air/fuel mixture goes lean. The transition is quick and abrupt, so the PCM has to keep track of the back and forth rich/lean transitions to estimate th...