Heated oxygen sensors are used to minimize the amount of time required for closed loop fuel control operation and to allow accurate catalyst monitoring. The oxygen sensor heater greatly decreases the amount of time required for fuel control sensors to become active. An Oxygen sensor heater is also required by catalyst monitor HO2S to maintain a sufficiently high temperature which allows accurate exhaust oxygen content readings further from the engine. The PCM will run the heater test only after a cold start (determined by engine coolant and intake air temperature at the time of startup) and only once during an ignition cycle. When the engine is started the PCM will monitor the HO2S voltage. When the HO2S voltage indicates a sufficiently active sensor, the PCM looks at how much time has elapsed since startup. If the PCM determines that too much time was required for the HO2S to become active, this DTC will set. The time it should take the HO2S to reach operating temperature is based on the engine coolant temperature at start-up and the average mass air flow since startup (higher average airflow or higher startup engine coolant temperature = shorter time to HO2S activity).

HO2S voltage remains within 150 mV of the bias voltage (about 450 mV) for a longer amount of time than it should. The amount of time ranges between 42 seconds and 2 minutes.