Diagnostic Aids

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2008 GMC Yukon XL, 2008 GMC Yukon, 2008 Chevrolet Tahoe, 2008 Chevrolet Suburban, and 2008 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

Verify that the ground connection for the STRTR relay ground circuit is clean and tight.
Inspect the terminals for the STRTR relay in the underhood fuse block for poor connections.