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Circuit Description

WARNING: This page is about a different car, the 2004 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.

The powertrain control module (PCM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy and emission control. Fuel delivery is controlled differently during the Open and the Closed Loop. During Open Loop the PCM determines fuel delivery that is based on sensor signals, without oxygen sensor input. During the Closed Loop the PCM adds oxygen sensor inputs to calculate Short and Long Term fuel trim fuel delivery adjustments. If the oxygen sensors indicate a lean condition, fuel trim values will be above 0 percent. If the oxygen sensors indicate a rich condition, fuel trim values will be below 0 percent. The values for the Short Term fuel trim change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long Term fuel trim makes coarse adjustments in order to maintain an Air/Fuel Ratio of 14.7:1. If the PCM detects an excessively lean condition, DTC P0171 will set.

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