Circuit Description

The heated oxygen sensor (HO2S) must reach operating temperature to provide an accurate voltage signal. A heating element inside the HO2S minimizes the time required for the sensor to reach operating temperature. Voltage is provided to the heater by the ignition 1 voltage circuit through a fuse. With the engine running, ground is provided to the heater by the HO2S heater low control circuit, through a low side driver within the engine control module (ECM). The ECM commands the heater ON or OFF to maintain a specific HO2S operating temperature range. The ECM determines the temperature by measuring the current flow through the heater. When the heater is in the ON state, the ECM will pulse the heater OFF for a duration of 50 ms, once per second. The ECM calculates the heater resistance on a cold start. This diagnostic will only run once per ignition cycle. If the ECM detects that the heater calculated resistance is not within the expected range, the following DTCs will set:

• DTC P0053 for HO2S sensor 1
• DTC P0054 for HO2S sensor 2