Circuit/System Verification
WARNING: This page is about a different car, the 2007 GMC Yukon XL, 2007 GMC Yukon, 2007 Cadillac Escalade EXT, 2007 Cadillac Escalade ESV, and 2007 Cadillac Escalade. However, it is still accessible from the selected car via links, so may be relevant.
With a scan tool observe the Tow/Haul switch parameter in Body Controls data list, operate the Tow/Haul switch several times, and observe the parameter as you operate the switch with the transmission in Drive. The parameter should toggle between Active and Inactive when the switch is operated.