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 control mode for at least one minute.
• Engine speed 1500-3000 RPM.
• ECT greater than 122°F (50°C).
• Canister purge duty cycle is greater than 2 percent.
• MAF 9-42 grams per second.
• 90 seconds after closed loop has been established, HO2S average transition time of 300-600 mV is too slow.
• Lean-to-rich average transition response time greater than 101 milliseconds.
• Rich-to-lean average transition response time greater than 150 milliseconds.