Oxygen Sensor Relay: Description and Operation

Oxygen Sensor Heater Relay:
If the vehicle is equipped with 4 oxygen sensors, a separate oxygen sensor relay is used to supply voltage to the sensor heating elements. This particular relay is used only for the 1/2 and 2/2 downstream sensors. Voltage for the other 2 sensor heating elements is supplied directly from the ASD relay. Refer to Wiring Diagrams to determine which relay is used. Electrical Diagrams

To avoid the large simultaneous current surge needed to operate all 4 sensors, power is delayed to the 2 downstream heater elements by the PCM for approximately 2 seconds.

Oxygen Sensor Heaters/Heater Relays:
Depending on the emissions package, the heating elements within the sensors will be supplied voltage from either the ASD relay, or 2 separate oxygen sensor relays. Wiring Diagrams to determine which relays are used.[1][2]Electrical DiagramsApplications and ID.