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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 335 (Engine Controls - Self-Diagnostics - 3.0L) >> Diagnostic Tests >> DTC P0135, P0141, P0155 0R P0161: Ho2S Heater Circuit >> Circuit Description

Circuit Description

WARNING: This page is about a different car, the 2003 Saturn Vue. 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 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 reduce the ON time to prevent thermal shock to the sensor components from moisture in the exhaust system. The ECM will not allow full HO2S heating until calibrated limits of time, temperature, and intake airflow have been reached. The ECM periodically monitors the HO2S operating state by briefly turning OFF the heater low side driver at regular intervals. A small reference voltage of approximately 3.6 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. The ECM calculates the HO2S element resistance based on the HO2S heater command voltage and calculated exhaust gas temperature. If the ECM detects that the HO2S heater element resistance is too high, the following DTCs will set:

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