Oxygen Sensor Relay: Description and Operation

PURPOSE
The Heated Oxygen Sensor (HO2S) relay allows the Powertrain Control Module (PCM) to regulate the flow of current to the HO2S heater circuit. The HO2S is heated during initial engine warm-up and during periods of prolonged idling when exhaust system temperatures are not hot enough to maintain the sensor above a minimum operating temperature of 600°F.

HO2S Heater Control Relay Diagram:

OPERATION
Battery voltage (12 volts) is applied to the HO2S relay through the ignition switch (when in run). Upon initial start-ups and during periods of prolonged idling the PCM will apply a ground signal to the HTR CONTROL circuit (PCM pin 14) which energizes the HO2S relay. The normally open relay then shuts and energizes the HO2S HTR circuit.