DTC P1133: Ho2S Circuit - Insufficient Switching - Bank 1, Sensor 1 & DTC P1153: Ho2S Circuit - Insufficient Switching - Bank 2, Sensor 1: Description

WARNING: This page is about a different car, the 2003 GMC Envoy XL and 2003 Chevrolet TrailBlazer. 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 compared the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The Powertrain Control Module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and closed loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream; low HO2S voltage indicates a lean exhaust stream. This diagnostic will only run once per ignition cycle. The PCM monitors the number or rich-to-lean and lean-to-rich transitions. A transition is defined as, the HO2S voltage changes fro above 625 mV to below 250 mV or from below 250 mV to above 625 mV. If the PCM detects that the number or transitions were less than a specified value, DTCs P1133 or P1153 will set.