I wish I knew. I have a 2002 Grand Cherokee that is doing the same thing.
Check the 2005 GMC Envoys turn signal flasher. The flasher could have an intermittent issue causing the signals to not work.
Try replacing turn signal flasher
turn signals and emerg flashers work off a flasher can. go to any auto store and buy a new one they are cheap and easy to replace
Have a 2003 jeep grand Cherokee trying to fined the junction box took covers off steering column but can't fined box.
Check the fuse
Either your turn signal bulbs are out or the wiring leading to your turn signals is not properly connected. Most likely your bulbs are out which will only cost a few bucks.
Because the hazard/turn signal relay has failed. A defective/intermittent turn signal switch can also cause this symptom.
It controls the windows and turn signals
More than likely the Flasher Relay is defective. Replace it.
let the wife reverse park in to a small space
most likely would be a bad turn signal flasher