DTC P0133: O2S1 Circuit - Slow Response: Description
WARNING: This page is about a different car, the 2002 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
This DTC tests within the Powertrain Control Module (PCM) and NOT within the Alternative Fuels Engine Control Module (AF ECM).
The PCM continuously monitors the Oxygen Sensor (O2S) 1 activity for 100 seconds. During the monitoring period, the PCM counts the number of times that the O2S 1 switches from rich to lean, and from lean to rich, then adds the time that the O2S 1 took to complete all the switches. With this information, an average time for all switches can be determined. Whenever the average time to switch is too slow, a DTC P0133 will set.