The power folding mirrors on GMC Sierra 1500 Denali AND many Chevy and GMC trucks are great mirrors UNTIL THEY BREAK and won't fold out. They break FREQUENTLY and the only "OEM" solution is to replace the whole mirror assembly which is expensive, especially at a dealer and if you can't do it yourself. The OEM folding mirror uses a plastic gear, and it breaks easily. It always seems to happen in the fall when the weather in CA is starting to go from hot to cooler. The last one I replaced lasted less than 3 years. I have had to replace mirrors on my truck at least 3-4 times in the 11 years I've had the truck. Currently, just the part is $450 ONLINE from a reputable dealer that sells discounted OEM parts, although I do still see some on ebay for about $250-$300. That's not including installation and that's a discounted price off what a dealer would charge you at the parts counter.

Previously, I was able to buy the mirror assembly for around $250 after my warranty ran out and I then installed the whole mirror assembly myself. I had an extended warranty that covered the first 2 or 3 replacements. Since I have a spare on hand from the last replacement (I kept the broken one), I'm going to attempt an aftermarket repair using a metal gear and a grounded motor from Gruven Parts (google them). At around $85 shipped for the gear+motor, it's much less expensive and I hope might provide a permanent fix. If the first one works, I'll probably rebuild the other 2 mirrors (kit of 2 gears plus motors is $99 plus shipping so about $120 vs one gear plus motor at $65 plus shipping= $86). This is a somewhat dangerous problem as you lose visibility and when this breaks, you cannot open the mirror and thus lose rear/side visibility while driving. And its really annoying because even if you replace the mirror once, you KNOW it's going to break again soon and require another repair. Like I said, I have had to replace 3-4 times now, at least. I've lost count... a very poor design.