Circuit Description

PCM continuously monitors HO2S activity for 100 seconds. During this period, PCM counts number of times HO2S responds from rich to lean and from lean to rich, and adds amount of time it took to complete transition. With this information, an average time for all transitions can be determined. If average response time is too slow, DTC P0133 will set.

A lean to rich transition is determined when HO2S voltage changes from less than 300 mV to more than 600 mV. A rich to lean transition is determined when HO2S voltage changes from greater than 600 mV to less than 300 mV. A sensor that responds too slowly is most likely defective and should be replaced.

For duplication of DTC, ensure:

• DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 or P1258 are not set.
• Engine coolant temperature is greater than 122°F (50°C).
• Ignition voltage is greater than 9 volts.
• Fuel system is operating in closed-loop.
• Engine speed is at 1000-2300 RPM.
• Engine airflow is 20-50 gm/s.
• EVAP canister purge duty cycle is greater than zero percent.