This bulletin applies to 2004-2011 Chevy Colorado and GMC Canyon 4WD vehicles. If you have a customer that complains about an intermittent unrequested transfer case mode shift, scan for DTCs and correct as needed.
Ensure that all power and grounds to the transfer case control module are clean with proper terminal fit. If nothing is noted upon inspection, replace the transfer case select switch. For 2006-2008 model year trucks, a revised transfer case switch can be ordered as P/N 20951985 (USA models) or 20951984 (Canada). This is the same update transfer case switch that was previously made available through WPC and engineering.
If you have completed all diagnostics and have replaced the transfer case switch and still have an intermittent un-requested shift to four-wheel-drive, then replace the transfer case control module with the latest part number.
The transfer case control module is plug-and-play and does not require programming or setup.