Circuit Description

After achieving "closed loop" fuel control, a commanded air/fuel ratio of 14.7:1, RPM between 1500-3200 and airflow between 7-25 grams per second, PCM will continuously monitor the front O2S signal for 100 seconds. During this time, the PCM counts the number of rich-to-lean and lean-to-rich switches. Voltage reading should be less than 300 mV and greater than 600 mV, to be considered a switch. The number of switches along with the time to achieve these switches are used to calculate the average response time to perform each switch. This information is also used to calculate if the proper ratio of the switches is correct.

The 3 DTCs are used to identify different types of faults that can occur with the O2S.

• P0133 (O2S Response Too Slow)
  
  This DTC is set if average response time of the switches from the sensor is too slow after the 100 second test time performed. If the lean-to-rich time is less than 94 ms or the rich-to-lean time is less than 125 ms this DTC will set.
• P1133 (Too Few Rich-To-Lean And Lean-To-Rich Switches)
  
  If less than 10 switches take place during the test, this DTC will set.
• P1134 (Rich-To-Lean Or Lean-To-Rich Ratio Error)
  
  If the transition ratio of the sensor is greater than 2.8 or less than 0.6, this DTC will set.