DTC P0135: Ho2S Heater Performance - Sensor 1: Description

WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2002 Pontiac Grand Prix, 2002 Pontiac Bonneville, 2002 Chevrolet Monte Carlo, 2002 Chevrolet Impala, and 2002 Buick Regal. 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 about 450 millivolts. The HO2S generates a voltage within a range of 0-1000 millivolts that fluctuates above and below bias voltage once in closed loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and provide an accurate voltage signal. The HO2S 1 heater performance diagnostic will only run from a cold start and only once per key cycle. This DTC will set if the HO2S 1 heater takes too long to heat based on the HO2S 1 signal voltage input to the PCM. The HO2S 1 heater circuit is energized anytime the ignition key is in the on position. The HO2S 1 has the following circuits:

HO2S 1 high signal.
HO2S 1 low signal.
HO2S 1 heater ignition 1 voltage.
HO2S 1 heater ground.