The EGO1 (Exhaust Gas Oxygen) sensor is a four-wire sensor that provides a very accurate output voltage which is directly correlated with air/fuel ratio. It is an ideal sensor for use with the ARM1 (Air/Fuel Ratio Meter). The EGO1 features an internal heater which assures accurate readings soon after engine start. The EGO1 also features a signal ground which provides highly accurate readings.