Oxygen (O2) Sensor Heater Relay

The oxygen sensor heater relay is located in the engine compartment, on right inner fender panel. See Figure . The ECU controls the O2 heater relay. The O2 heater relay is normally closed, which then supplies voltage to the O2 sensor heater during warm-up and idle conditions. When the speed sensor and MAP sensor reach a predetermined input (when exhaust heat is sufficient enough to heat the O2 sensor), the ECU can open the O2 sensor relay by opening and closing the relay's ground path.