Circuit Description

The PCM will continuously monitor the front oxygen sensor signal for 100 seconds after achieving closed-loop fuel control and when RPM is within range. During this time PCM counts the number of rich-to-lean and lean-to-rich switches. To be considered a switch, voltage must go less than 300 mV and greater than 600 mV. PCM also keeps track of time it takes to make the 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 proper ratio of switches is correct.

DTC will set when the number of rich-to-lean counts are less than 1 (A/T) or 2 (M/T), or lean-to-rich counts are less than 1 and the following conditions are met:

• DTC P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, P0201, P0202, P0203, P0204, P0300, P0301, P0302, P0303, P0304, P0336, P0440, P0442, P0446, P0506, P0507, P0601, P0602 or P1441 is not set.
• Engine speed 1600-2400 RPM (M/T) or 1800-2300 (A/T).
• TP angle 8-15 percent.
• Evaporative purge is commanded to 80 percent or greater.
• Purge learned memory is greater than 220.
• ECT greater than 167°F (75°C).
• System in closed-loop mode.
• Engine running more than 10 seconds (M/T) or 200 seconds (A/T).