DTC P1133: Ho2S Circuit - Insufficient Switching - Sensor 1: Description
WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
The Powertrain Control Module (PCM) continuously monitors the Heated Oxygen Sensor 1 (HO2S 1) activity for 100 seconds. During the monitoring period, the PCM counts the number of times that the HO2S 1 switches from rich to lean, and from lean to rich. You can determine a total for all of the switches with this information. If the number of switches is too low, a DTC P1133 will set.