DTC P0135 & P0155: Ho2S Bank 1& 2 Sensor 1 Heater Circuit: Description

WARNING: This page is about a different car, the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, and 2002 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

The Heated Oxygen Sensor (HO2S) is used in order to determine the oxygen content of the engine's exhaust. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the engine is operating lean, the exhaust will have more oxygen content. Once at operating temperature, the HO2S will produce a voltage in relation to the oxygen content of the exhaust. The HO2S requires an operating temperature of 600°F (360°C) to produce voltage. The HO2S will produce more voltage when the exhaust is rich and less voltage when the exhaust is lean. The HO2S operating voltage range is between 0.10 volt (100 mV) to 1 volt (1000 mV).

The PCM supplies a bias or reference voltage to the HO2S. This bias voltage is around 450 mV. The AF ECM monitors the bias voltage as well as the voltage produced by the HO2S.

During normal closed loop fuel control operation, the AF ECM will add fuel (enriches the mixture) when the HO2S indicates a lean exhaust content. When the HO2S indicates a rich exhaust content, the AF ECM will subtract fuel. This oscillation above and below the bias voltage, sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.

The oxygen sensor contains a heater. The heater is necessary in order to quickly warm the sensor to operating temperature. The heater will also maintain operating sensor temperature during extended idle conditions. A functioning oxygen sensor heater will allow the sensor to produce voltage in a short amount of time. A sensor at operating temperature will cause the HO2S signal voltage to go above or below, depending upon exhaust oxygen content, the bias voltage.

This DTC is used to indicate an HO2S signal voltage that did not leave the cold sensor bias voltage range in an acceptable amount of time.