Oxygen Sensor Relay: Description and Operation

Relay Cluster Location -- On Right Front Wheel Well:

This output device is normally energized by the ECU. When energized the relay sends current to the Oxygen sensor heater, when de-energized no current is allowed to flow to the Oxygen sensor. The ECU controls this relay by applying or removing the ground from the circuit.

The relay is energized under warm-up and idle conditions, and is de-energized when the ECU receives signals that the Oxygen sensor will remain heated by the exhaust. The ECU receives inputs from the following sensors to determine at what time the relay should be energized or de-energized:

^ Engine Speed Sensor
^ MAP Sensor

The Oxygen sensor heater relay also acts as a source of battery voltage for the fuel pump relay under certain conditions.