DTC P1133: Ho2S Insufficient Switching (Bank 1; Sensor 1 - SOHC): 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.
The Powertrain Control Module (PCM) continuously monitors Heated Oxygen Sensor (HO2S) 1 activity for 100 seconds. During the monitor 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, DTC P1133 will set.