DTC P0135, P0141, P0155 & P0161: Ho2S Heater Circuit - Bank 1 & 2, Sensors 1 & 2: Description

WARNING: This page is about a different car, the 2002 Pontiac Firebird and 2002 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.

The Powertrain Control Module (PCM) supplies a bias voltage approximately 450 mV, on the Heated Oxygen Sensor (HO2S) signal high and low signal circuits. When you turn the ignition to the ON position, battery voltage is supplied to the HO2S heater. As the heater reaches the operating temperature, the HO2S voltage responds by changing from a bias voltage range to the normal operation. Typically, as the HO2S reaches the operating temperature, the HO2S voltage goes from a bias voltage to a voltage below 300 mV. Depending on the exhaust gas content, the HO2S voltage can go above 450 mV. The PCM runs the heater test only on a cold start, depending on the cumulative air flow, and only once an ignition cycle. When you start the engine, the PCM monitors the HO2S voltage. When the HO2S voltage goes above or below the bias range threshold, the PCM determines how much time this process took. If the PCM detects that the process took too much time for the HO2S to enter into normal operating range, a Diagnostic Trouble Code (DTC) sets. The time the process takes the HO2S to reach operating temperature is based on the amount of air that flows into the engine.