DTC P0171 & P0174: Fuel Trim System Lean - Bank 1 Or 2: Description

WARNING: This page is about a different car, the 2001 GMC Savana, 2001 Chevrolet RV Cutaway, 2001 Chevrolet Cutaway, and 2001 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

Powertrain Control Module (PCM) controls air/fuel metering system to provide the best possible combination of driveability, fuel economy and emission control. Fuel delivery is controlled differently during open and closed loop. During open loop, PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During closed loop, oxygen sensor inputs are added and used by PCM to calculate short and long term fuel trim (fuel delivery adjustments). If oxygen sensors indicate a lean condition, fuel trim values will be more than zero percent. If oxygen sensors indicate a rich condition, fuel trim values will be less than zero percent. Short term fuel trim values change rapidly in response to Heated Oxygen Sensor (HO2S) voltage signals. Long term fuel trim makes coarse adjustments in order to maintain air/fuel ratio of 14.7:1. DTC P0171 or P0174 will set if PCM detects an excessively lean condition.