System Description
WARNING: This page does not describe the selected car, but rather 15 other vehicles, including the 2003 Hummer H2, 2003 GMC Yukon XL, 2003 GMC Yukon, 2003 GMC Sierra, and 2003 GMC Savana. However, it is still accessible from the selected car via links, so may be relevant.
Scan tool first energizes fuel pump and then injectors for a precise amount of time allowing a measured amount of fuel into manifold. This causes a drop in system fuel pressure that can be recorded and used to compare each injector.