DTC P0172 & P0175: Fuel Trim System Rich, Bank 1 & 2: Description

WARNING: This page is about a different car, the 2002 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.

Powertrain Control Module (PCM) controls air/fuel metering system in order to provide 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 PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During closed loop the PCM adds oxygen sensor inputs to calculate short term 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 an air/fuel ratio of 14.7:1. Fuel trim diagnostic will conduct a test to determine if a rich condition actually exists or if excessive vapor from EVAP canister is causing a rich condition. If the PCM detects an excessively rich condition, this DTC will set. If the PCM detects excessive vapor then a pass is logged.