DTC P0135: Ho2S Heater Circuit (Bank 1; Sensor 1): Description

WARNING: This page is about a different car, the 2002 Pontiac Sunfire, 2002 Pontiac Grand Am, 2002 Oldsmobile Alero, and 2002 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the Powertrain Control Module (PCM) operates in an open loop mode, ignoring the HO2S signal voltage when calculating the air/fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of 450 millivolts. The HO2S generates a voltage within a range of 0-1000 millivolts, that fluctuates at greater than and less than bias voltage once in closed loop. High HO2S voltage output indicates a rich fuel mixture; low HO2S voltage output indicates a lean mixture. A heating element inside the HO2S reduces the time required for the sensor to reach operating temperature, and provide an accurate voltage signal.

The HO2S heater diagnostic runs continuously when the heater circuit is energized. The HO2S heater circuit is only energized when the engine is running or commanded ON by the scan tool. The DTC will set if the heater current is at greater than or less than a calibrated threshold for 200 seconds.