Diagnostic Aids

WARNING: This page does not describe the selected car, but rather 13 other vehicles, including the 2002 GMC Yukon XL, 2002 GMC Sierra, 2002 GMC Savana Special, 2002 GMC Savana Camper Special, and 2002 GMC Savana. However, it is still accessible from the selected car via links, so may be relevant.

Fuel contamination, such as water and alcohol, will affect fuel trim.
A malfunctioning MAF sensor can cause a rich condition and set this DTC. See DTC P0101: MASS AIR FLOW SENSOR PERFORMANCE .
Using a scan tool, review the Failure Records. If an intermittent condition is suspected, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM.