WARNING: This page is about a different car, the 2010 GMC Sierra and 2010 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
J 38522
Variable Signal Generator
Fig 1: J 38522
Courtesy of GENERAL MOTORS CORP.
The purpose of this test is to provide a simulated output speed sensor signal to the control solenoid valve assembly.