Circuit Description

PCM monitors the HO2S signal voltage and adjust fuel delivery based on signal voltage when system in "closed loop". A change made to fuel delivery will be indicated by the long and short term fuel trim values which can be monitored with a scan tool. Ideal fuel trim is about zero percent. If HO2S signal is indicating a lean condition, PCM will add fuel, resulting in a fuel trim greater than zero percent (100 percent maximum lean). If rich condition is detected, fuel trim values will be less than zero percent (-99 percent maximum rich), indicating that PCM is reducing the amount of fuel delivered. If an excessive lean condition is detected, DTC will set.