Circuit Description

PCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change made to fuel delivery is indicated by the long and short term fuel trim values. Ideal fuel trim value is about 128 (zero percent).

A fuel trim value of more than 128 indicates that PCM is adding fuel to compensate for a lean condition. A fuel trim value less than 128 indicates that PCM is reducing amount of fuel to compensate for rich condition. DTC will set if PCM detects an excessively lean condition.