i’m taking it to the dealer soon, but I had a 2021 Duramax 3 L with similar system and absolutely no problems. Just wondering what could causes.

I recently found out the CEL is probably the result of the recent over the air update. GM released a TSB. 

This was my post.

I have a GMC Yukon XL 2017. 
For the last month, it has done this thing where as I’m driving, it randomly decides to show “Anti-Theft Deterrent System” along with other messages like “Airbag” and “Park Assist System”. As it’s doing this, the gauges all fall and it stays like this for like a couple of seconds and then it randomly comes back to normal and the messages even go away. The thing is that while this is happening, the engine is running fine. I can accelerate even with all this going on so it’s definitely an electrical issue. Click the link I sent so you can better see what is going on. I’d appreciate any advice you have.

Current Mileage: 82000

Right out of the gate we had some initial problems with it as it drank 5+ quarts of oil in the first 2-3000 miles off of the showroom floor. Didn't discover it until we accelerated and it threw a low oil pressure code. Dealer was great and worked with us and finally figured out that somehow despite our valve cover having the correct part number based on a TSB, it was the old part that was having excessive oil consumption (likely vacuum). So they replaced that and one glow plug that went out and that specific issue has been fine ever since. Only throwing this issue in there as it's how we started out with this vehicle and it resulted in the dealer giving us a 120000 mile extended warranty.  Absolutely love it though.

So we don't tow often with this vehicle and before 50,000 miles the only thing we towed is our pontoon boat which is maybe 2500 lbs. So nothing.... Around 50,000 miles we suffered our first transmission issue. We were driving home towing the pontoon on a flat road going a steady speed of 55 mph and suddenly the vehicle shook really hard like I ran over a really hard transition in the road but it kind've felt like the boat was pulling me back really hard. And then it did it again about 5 seconds later. I pulled over thinking I had a problem with my trailer and couldn't find anything wrong. Drove home without issue and shortly after this got the transmission flushed.

After this event we bought a travel trailer and never once had an issue while towing it. At around 60,000 miles we were driving up a mountain going a steady speed of 35mph with all of my kids in the car and the vehicle did the same thing as before. Shook violently 2 times in a row. Pulled over, got real nervous as we had a long ways to go to continue going up the mountain so we turned around. Took it to a Chevy dealer that was local to where we were on vacation and they couldn't find anything wrong. Suburban finished the trip without issue. Maybe 6 months later it did it again but it was while towing a lightweight utility trailer with a single sportbike (total weight of maybe 1500 lbs) on it going steady speed of 50mph. Difference was it did it just once. Shook violently. Then it did it 2-3 more times in a 5 - 10 minute span before I was able to safely pull off of the highway. I cycle power and it seemed to go away after that as I had another 2 hrs to drive home.

Around this time I contacted a local dealership and explained the problem and they started working with me to help troubleshoot since it couldn't be replicated. They updated the TCM software and said if it happened again I'd likely be looking at a new valve body. This was last fall in 2025. Right around Christmas the vehicle did the violent shifts again 4-5 times at different speeds and we drove straight to the dealer since we were in town. Dealer confirmed they'd be ordering a valve body and we'd have to wait for it to show up. 

About a week or two later before the valve body showed up I was driving my kids to town and it did it again. But this time the vehicle was struggling to find a gear and was lurching real bad. I thought the vehicle was actually gonna die on me. It eventually threw a couple codes and limited my speed. Code was: P0336. Limped it to the dealer about a week before the valve body showed up and left it there.

Got the valve body replaced at 77,000 miles and only noted issues were during the learn period it shifted rough but I assumed it was 100% related to the learning (mechanic told me don't be alarmed by this). After about a month of a good mix of driving at city and highway speeds we never had an issue. 5000 miles later now at 82000 miles and about 4 months, its started shifting hard randomly. Kids will ask did we hit something or did someone rear end the car. It's happened in 2 different scenarios where once it was accelerating lightly away from a light and the other with cruise control on going 50 mph. 

Currently have an appt to drop it off on Monday but not expecting much other than we'll keep an eye on it. Not once has the vehicle actually thrown a TCM code, and it's been a-typical to what I've found online. The P0336 issue for instance, the best we can assume is because the valve body was searching for a gear that the engine in turn threw a code because the transmission was basically making it run super rough. I know this is long winded but I'm at the point that I'm losing confidence in this vehicle being my wife's vehicle to take the kids around in. I could care less if it breaks while I'm in it but I don't want her getting stuck in it with all of my kids.

I did ask the dealer about a full trans replacement and it seems that they're hesitant to do that unless they find metal or that the fluid looks bad. So not holding my breath.... Also wondering if we're chasing the wrong thing entirely and need to look more at the crankshaft position sensor (P0336) and see if there's a chafed wire or bad connection, etc. Any help is appreciated.

~Joe

Owners manual lists both 80W-90 non-synthetic and 75W-90 synthetic. Which was factory fill? Which would a GM dealer use for a current day drain and fill? 

I know the manual states that there is a maximum load of 375 lbs that can be applied to the tailgate so I assume this bracket must be rated at or below that amount?

I have checked the grounds at G200 and G201, both are clean. I have 11.9V at the red wire in the overhead console but 10.5V on the orange. If I probe the red wire to ground it goes from 11.9V with headlights off, and to 11.7V when the headlights are tunred on, if I probe the orange wire I get 10.5V with the lights off but 6.3V with the lights on.

I have probed the overhead black wire to both G200 and G201, if I probe to G201 I get .7 megaohms resistance but after a few minutes that steps down as modules go to sleep, after about 25 sec it drops to 360 ohms then to 210 ohms then down to .4 ohms.

I have cleaned the gronds under the RF radiator support, the grounds at the LR of the frame.

The only thing that comes to mind, is about a year ago, my LR was hit and I didn't notice any damage behind the bumper, about 6 months later during heavy rain, I would get random parking sensor blocked errors on the DIC but the sensors still worked. Later on the LR sensor stopped working and I had a code that came up in the Tech 2 as:

I did disconnect all 3 connections at the module in the LR cargo area and my issues still remain.

I have reseated all the junction block connectors behind the left and right panels in the front door area at the dash, not sure where to check or if the shorted sensor caused an issue with the BCM.

Everything works in the vehicle except the map lights dim the IC lights when pressed but no light turns on, and the obstacle avoidance is not working until I replace that sensor.

All input and criticism appreciated.

Looking for a screenshot of a known good CKP Active Counter chart line or a definitive opinion on the one below. Chasing down the infamous intermittant CKP signal loss and as far as I know, the active counter should steadily increase until it gets to a high value and then drop back to zero.  My CMP Active Counter does this but my CKP Active Counter (when it works) is all over the place and fluctuates wildly.  For reference, CKP AC on top, CMP AC on bottom:

I feel like this is an issue but the only other vehicle I have to compare to is a 2018 Mazda and it doesn't use a CKP Active Counter at all.  If this is normal, then I can start looking in other areas.  If it's not normal, I can start to figure out why (suggestions welcome).  

The root issue I'm trying to solve is an intermittant loss of signal from CKP (Circuit A).  Textbook signal loss symptoms: Engine will crank for an extended period and then start off of the CMP signal in low-power mode with no tachometer and stabilitrak warnings.  Happens maybe 50% of the time.  If I shut it off immediately and attempt to restart, it will usually set a P0335 code.  Most times If I drive long enough to warm it up, then shut it off and let it sit for 15-30 mins (shopping visit, getting gas, etc), it will restart normally and run fine.  Almost like something (maybe the CKP sensor) is heat-soaking and making contact, then allowing a normal restart on the next cycle.   Turning ignition off and then immediately restarting does not clear the issue.  It has to sit for a little while.

I'm already well aware of the standard P0335 diagnostic procedure and will do that eventually but I haven't been able to catch it when it's actively failing.  Most times when it happens, I have somewhere to be and don't have time to look at it.  By the time I get home it's already working again.  I've read quite a few accounts of other people who have had this problem, gone through the procedure, replaced CKP or ECM or both and still not solved the problem.  I'm trying to be more methodical and not call in an artillery strike from the parts cannon.  The battery is new (needed one anyway), the alternator charges correctly and the main ground on the left lower engine block is intact and not corroded (life in Texas, yo).  Voltage at battery exactly matches ECM/OBD voltage, so bad battery cables are doubtful.  I already replaced the CKP connector and the ignition switch (thinking it might be an intermittant power signal to the ECM... they're cheap parts).  Have not replaced the CKP sensor yet but it's in my cart to buy (Genuine GM, of course).  

Any input is appreciated.

Thanks

My question is, If I were to install a factory 84488395 Trailer Brake Control Switch Assembly, would it conflict with the existing CURT controller?

ALAO, MY truck did not come with Fog Lights, What is the exact GM part number for the Fog Light Kit?  Also, IF I were to install this Fog Light kit, would I need to FLASH the BCM?

I just bought a 2008 Sierra 1500 XLT. The left signal flasher does not work. The right side functions fine. When the headlights are on all of the lamps function correctly. When the flashers or the signals are activated the left side flashes normal 3 times and then fast from there on. I replaced the multi switch stock on the column. When the flashers are are activated the fuse blows which tells me there is a short somewhere...I guess. Why would the lamps work if the headlights are on if their is a short? Where would I look for a short? The wires seem to be covered in a loom except at the housing itself and I did not see any bare wire or rub spots. Is the flasher split into a right and left side? If so where is the flasher control?

Any in site would be appreciated.  Thanks!

This mirror was replaced shortly after purchase for going to extremes and clicking.

It then worked fine for 5 years .... Now it starts searching for position every time I would start up the truck.

On very rare occasion it will start and actually go to my memory setting.

Please don't tell me how to reset the memory .. it's been done so many times my finger is getting tired.

I've also disconnected the battery multiple times.

I don't know if this helps find a solution:

When I start the truck and the mirror moves ending looking at the sky or road .... I've tried to press driver 1 and or driver 2 ..... nothing changes.

The truck has been to the dealer multiple times with NO SOLUTION ...

The dealer has told me this is not a new problem to them and they have no long term cure ...

Anyone here have a fix?

Hey guys.

Just really stumped here and never got to the bottom of this. I’ll post a video and in that video I was curious what that fluttering/ticking sound is when I’m only on throttle? Is it the hpfp? Manifold leak? Or is this normal. Feel free to ask any more questions to get a better idea. 
 

edit: 
 

windows down:

https://youtube.com/shorts/H7UPcljXE_M?si=dWSUeyZBbD8uDOdn

windows up:

https://youtube.com/shorts/voeOH1NHV-M?si=5vWRHW5FwOoRbkpP