DTC P0172 & P0175: Fuel Trim System Rich - 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. Fuel trim diagnostic will conduct a test to determine if a rich failure actually exists or if excessive vapor from evaporative emission canister is causing a rich condition. DTC P0172 or P0175 will set if PCM detects an excessively rich condition. If PCM detects excessive vapor then a pass is logged.