Circuit/System Description

WARNING: This page is about a different car, the 2010 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.

Heating elements inside the heated oxygen sensor (HO2S) minimize the time required for the sensors to reach operating temperature and provide an accurate voltage signal. A low side driver within the engine control module (ECM) is pulse-width controlled to provide current to the heater elements. The ECM will not allow continuous HO2S heating until calibrated limits of time, temperature, and intake airflow have been reached. The ECM continuously monitors the HO2S heater current draw and operating state by briefly turning OFF the heater low side driver at regular intervals. A small reference voltage of approximately 4.9 volts is present at the heater low control circuit. When the low side driver is commanded ON the reference voltage is low. When the low side driver is commanded OFF the reference voltage is high, close to battery voltage. If the ECM detects that the predicted voltage and the detected voltage are different, a DTC sets.