Circuit Description

Heating elements inside the heated oxygen sensor (HO2S) minimize the time required for the sensors to reach operating temperature, and to 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. During warm-up the ECM will pulse the heaters ON-OFF to prevent thermal shock to the sensor components from moisture in the exhaust system. 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 is present at the heater low control circuit. When the low side driver is commanded ON, the reference voltage is low, 2.6-4.6 volts. When the low side driver is commanded OFF, the reference voltage is high, close to battery voltage. The ECM calculates the HO2S heater element resistance based on the actual heater current. If the ECM detects that the HO2S heater element resistance is too high, DTCs P0135, P0141, P0155, or P0161 will set.

Each HO2S has the following circuits:

• The HO2S high signal circuit
• The HO2S low signal circuit
• The HO2S heater ignition 1 voltage circuit
• The HO2S heater low control circuit