Circuit Description

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 will observe the activity of HO2S to determine if it has become active within a certain time period, after start-up. If the sensor has not become active within an expected time period, after start-up, the ECM will force a rich and lean state and wait for a response from the sensor. If the sensor still does not respond, a failure is reported and DTC P0135 or DTC P0155 will set. If the sensor is active within an expected time period, after engine start-up, the ECM will wait a calibrated amount of time and then begin calculating the temperature of the sensor. If the temperature of the sensor moves outside a calibrated range, a failure counter is incremented. If the number of failures exceed a calibrated amount, DTC P0135 will set for bank 1 sensor 1 or DTC P0155 will set for bank 2 sensor 1. A small reference voltage of approximately 4.5 volts is present at the heater low control circuit.