Circuit Description

PCM monitors Heated Oxygen Sensor (HO2S) activity for 90 seconds after closed loop operation has been enabled. During this test period, PCM counts number of times HO2S signal voltage crosses rich-to-lean and lean-to-rich threshold. If PCM determines that HO2S switching was insufficient, DTC P1134 will set. A lean-to-rich switch is determined when HO2S voltage changes above and below 450 millivolts. With this information, an average time for all transition can be determined. PCM divides rich-to-lean average by lean-to-rich average to obtain a ratio. If HO2S ratio is not within this range, DTC P1134 will set, indicating HO2S is not responding as expected to changes in exhaust oxygen content.