Circuit Description

WARNING: This page is about a different car, the 2003 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

The Engine Control Module (ECM) 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 Open Loop and Closed Loop. During Open Loop, the ECM determines fuel delivery based on sensor signals, without Oxygen Sensor (O2S) input. During Closed Loop, the ECM adds oxygen sensor inputs to calculate the short and long term fuel trim. If the oxygen sensors indicate a lean condition, the fuel trim values will be above zero percent. If the oxygen sensors indicate a rich condition, the fuel trim values will be below zero percent. The short term fuel trim values change rapidly in response to the HO2S voltage signals. The long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. This DTC is continuously monitored during engine operation. If ECM detects an excessively lean condition, DTC P0171 sets.