Circuit Description: Notes

The DTC P0133 Heated Oxygen Sensor (HO2S) Slow Response Sensor 1 diagnostic detects an unresponsive oxygen sensor. The powertrain control module (PCM) continuously monitors the heated oxygen sensor (HO2S) activity. The PCM counts the number of times that a rich-to-lean and lean-to-rich response is indicated and adds the amount of time required to complete all the transitions. The PCM uses this information in order to determine an average time for each transition. A DTC P0133 will set if the average transition time is too slow.

A lean-to-rich transition is indicated when the HO2S voltage changes from less than 300 mV to more than 600 mV. A rich-to-lean transition is indicated when the HO2S voltage changes from more than 600 mV to less than 300 mV. An HO2S that responds too slowly may be faulty and should be replaced.