Circuit Description

PCM provides about .45 volt reference to Heated Oxygen Sensor (HO2S). HO2S sensor signal varies from about one volt when exhaust is rich to about .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 related DTCs set.
• ECT is greater than 140°F (60°C).
• Engine operating in Closed Loop.
• Engine has been running for at least 2 minutes.
• Engine speed is 1500-3500 RPM.
• Canister purge solenoid duty cycle is greater than 2 percent.
• Calculated airflow is 17-32 g/second.