MyGMC2020

I was having a similar issue and currently has me stuck. I was seeing around 180 degrees in the dead of cold we had last month. I replaced the thermostat with a Napa brand, but it was stuck closed....replaced it with another aftermarket unit from another store, it was very slow to open. At least it was warm in the truck, and the gauge was reading 210...Then noticed fans were noisier than usual...Connected the gm scanner and noticed the temp sensor was reading 220-230. I knew high-speed fans would kick on at 233 degrees. I checked the top of the t-stat housing, which was hot, but the upper rad hose was cold. So replaced another t-stat. The upper hose gets hot as it should, which tells me it is opening at least, however, the fans will run as they should sometimes and sound like a jet other times. temp gauge steady at 210. Knowing the fans are indirectly controlled by the sensor, I ohm it out and found it was 200 ohms off of spec. I know this wouldn't be a deal breaker, but I figured I'd replace it anyway. This did drop my temps by only a few degrees in the scan tool and was a little closer match to the IR temp gun. With all of this, I was still noticing the fans on at random times. I thought maybe it wasn't circulating as it should so I tossed a water pump on it. Still no change. I'm still leaning toward the thermostat being the issue as I do notice temps in the scan tool that corresponds with the range the fans should run in the service manual. Keep in mind the fan does not stay on after the truck is off, and the temp gauge is showing 210 as it should. The cab temp is working as it should. Everything in the cooling system triangle is new with OEM except the thermostat. The service manual also states the fans will run if the AC pressures are too high, which I know its winter for me but with automatic temp control I know the AC will run year-round. Just strange that would randomly increase. so I went to the local dealer and was told it would arrive in July. I scour the internet for an OEM unit and nothing. It's like they had a flash sale on them and POOF...gone. I guess after I have written this short story if anyone else has seen this happen and/or if I'm right to think the aftermarket world is not able to make the thermostat as GM requires?

I went to my local dealership about a month ago to have them look at the rear park assist. I am told they updated the park assist module; however, they needed to replace 3 of the 4 sensors. (@$250 each). I declined the repair, only to reach out to a GMC parts place and get the sensors myself and put them in. I disconnected the battery and replaced all 4 sensors. I plugged the battery back in and to my suprise it was working until I go to put in reverse and then it stopped beeping only to display “Service park assist” again. I go to the dealer this morning and explained how this still doesn’t work. They tell me the new sensors need to be “woke up”, they were never meant to be installed in a driveway. I have 15 years working in the industry for a different manufacture and clearly not sure if this is a real thing or not. I have scoured the service manual with nothing regarding this either. Can someone shed some light on this for me??

So I swapped bulbs, replaced bulbs, and still had the issue. I ended up adding a jumper between the two yellow wires on pins 6-7 that control the headlights from BCM....and just like that zero issues. I would guess the output circuit was not strong enough to power the ballast on the passenger side. I know this isn’t a desired fix and perhaps I’ll build a pair of relays to offset the draw on the bcm. I’m having a bunch of phantom electrical issues and know why they traded this truck in. No one gets rid of a good vehicle.

Purple hue was a HID bulb that was going bad. I have the 2016 Sierra SLE and I have the factory hid. Love them...when they work. I have the passenger side that will not come on some times. Starting to think it’s a bcm, but not ready to drop cash for dealer to program new one.