Circuit Description

PCM provides about 0.45 volt reference to Heated Oxygen Sensor (HO2S). HO2S sensor signal voltage varies from about one volt when exhaust is rich to about 0.1 volt when exhaust is lean. PCM counts number or times a rich-to-lean and lean-to-rich response is indicated and adds amount of time it takes to complete all transitions. PCM uses this information to determine average time for each transition. If average response time is slow, DTC P0133 will set.

Conditions required to set DTC are:

• No CKP, ECT, EGR pintle position, IAT, MAF, MAP or TP sensor DTCs set.
• No EVAP system DTC set.
• No fuel injector circuit, fuel trim or misfire DTCs set.
• Engine running in closed loop fuel mode for at least one minute.
• Engine speed 1000-3000 RPM.
• ECT greater than 185°F (85°C).
• MAF 15-28 grams per second.
• Lean-to-rich average transition response time greater than 153 milliseconds.
• Rich-to-lean average transition response time greater than 148 milliseconds.