6sigma

I had an intermittent P25A2 code and they updated the EBCM. I'm under 36k miles so warranty work, but technically I think that falls outside the powertrain warranty so might not be covered if bumper to bumper is expired. The CEL happened a couple times before I got this flash update. I also had a P147B for a particulate sensor that needed to be replaced.

I have 10k miles on my 2020 Sierra AT4 CarbonPro I got in early 2020. It's been a great truck, just a few minor concerns/questions. 1. I've had 2 CELs, both some code that has something to do with the brake system. Both went away almost immediately, so never even got a chance to have the dealer look at it. Have not had one recently and I wonder if some software update along the way may have addressed this. 2. I have the adaptive cruise and it works well. My complaint is when traffic clears in front of you, the truck drops the hammer and downshifts to about 4k rpm. The minimax has enough torque it does not need to downshift and rev to the moon. I think the trans programming could be better adapted to suit the dmax. 3. I've noticed if it idles for 5 or so minutes it will sometimes move into a high idle mode, even in high air temp and when the engine is warm. Similar to when it is in regen mode but I don't think it is doing a regen. I assume it does this to keep the cat/DPF hot, but what seems weird is that it seems to stay in this high idle mode even after driving around some. I don't think it is a problem, just seems odd and I don't understand what it is doing. Actual regens are only slightly noticeable with a higher idle and a change in exhaust tone. I've had a couple regens start immediately after long highway drives, which is bad timing cause I've been in stop and go slow speed traffic and it's trying to regen. Again, not a problem, but would have been more efficient if regen'd at highway speed. My wish list is short. 1. Display the current gear somewhere 2. I'd like a boost gauge option 3. I'd like a light or indicator of when it is in active regen mode 4. Change the trans programming to hold a gear with more throttle (don't downshift as readily) since this thing makes peak torque at like 1600 rpm. 5. Tune the exhaust brake to be more effective. I don't really know if it is doing something or not. Maybe I've never had it in a scenario where it has really needed it. If it really is there, make it more effective. Overall love the truck and 10/10 would buy again. In fact, if the 2022/3 refresh looks good I may upgrade and get the same truck again.

I've noticed the UPS and FedEx trucks shut off the engine every time they stop now. I'm guessing they've done the analysis on fuel savings versus wear and tear on the trucks. Or maybe they do it just to signal they are doing something to reduce emissions on deliveries. I've got a 3.0 diesel and I usually press the button every time. Sometimes I forget and when it shuts off I'll hit the button. But I've wondered how much wear and tear on the starter actually occurs versus the fuel savings. There is no real data on this anywhere that I can find. With the DI system the restart is nearly instantaneous. I worry about turbo cooling with zero oil pressure but again, I've heard that is no longer an issue with modern turbos (nobody uses the turbo timers anymore). I think I'll just continue to press the button. A diesel at idle uses very little fuel.

What do you think of the auto stop/start system in these trucks? I'm curious how many just leave it enabled in the default setting or turn it off every time.

I hadn't seen that before, thanks for posting. Good info there. I'm not worried about the oil drive belt at all. I am more concerned about DPF life and overall complexity of all the various control systems. Fortunately there is a 5-year warranty so there is enough time to see if there are common weak spots.

Ft Wayne, Indiana assembly builds some crew short box. I am pretty sure all the CarbonPro trucks are built at Ft Wayne because the carbon bed supplier is very close by. I don't think the engine choice has much to do with where the truck is built though.

I've been thinking about this, but it looks like you have to take the dash apart to install it? How bad is the install? I'm getting better at remembering to hit the button but still forget sometimes, and then it shuts off at a stop and I think I should get the disabler!

Put a couple hundred miles on the 3.0 today. Best MPG over 50 miles was 30.9 according to the computer. I noticed MPG goes down a lot when you get above 75. 80mph is 20-22mpg on the display. Really happy with this truck and engine. Truck is an AT4 with 20" wheels.

Mine seems to regen about once every 10 hours of engine time. Engine time seems to be more accurate estimate of when it might regen than miles, since it depends on how it is driven. I wonder if driven a lot at highway speeds or under load towing that it might get hot enough to do some passive regen? Also I wonder if cold starts produce a lot of soot that might cause the filter to fill sooner.

Pretty sure it is the DEF sloshing in the tank. I once noticed something like you described after I topped off the DEF tank and moved the truck.

I think all the CarbonPros are built in Ft Wayne. The carbon bed supplier is located right outside Ft Wayne in Huntington, Indiana. This C&D article says a little more about it. My truck has been great so far - no quality issues yet. I like the idea that the truck is built in my home state.

The LM2 seems to be setup to warmup up relatively quickly for a diesel. I've been monitoring various temps with Torque app and it shows the exhaust temps inc DPF get to 400+F pretty fast (5 min maybe). Oil temp seems to get to 180-190 about the same time as the LT1 in my Camaro. Coolant temp takes longer to get hot though but I think that is by design in the active cooling system. It seems LM2 is setup to get emissions equipment up to temp quickly. Agreed that a lot of short trips are prob not ideal for any diesel though. If you have a lot of short trips I'd make a point to get it out on the highway occasionally to let everything get hot. I had a 2013 VW Passat TDI 2.0 when I had a 100+ mile daily round trip. That TDI was known to have frequent turbo failures, but my car never did and I think it was because everything got fully up to temp with almost no short trips.

Personal preference, but I found the black chrome trim to look a little off on a black truck. Like it was trying to match but didn't. Not enough contrast for my taste. White paint seemed like too much contrast so I chose the only other color available - satin steel. I think it looks pretty good with the 20" gray wheels. One thing I don't like is the chrome side mirror caps that I think comes with the tech package. It's the only real chrome trim on the whole truck. I think it's just a part of the Tech package that wouldn't matter on the other trucks but on the black chrome CarbonPro it looks off. I might look around for black caps or see if I can remove the chrome caps. Not a huge thing but something I notice.

I don't think any have been made in Carbon Metallic yet - supposed to be available in Spring sometime. I assume it is a metallic black.

Mine is still new but like it so far. I added the rubber bed mat to keep things from sliding around and better for my dog to walk on. I haven't noticed any noise difference. I had read somewhere on here that you lose the bed lights with the carbon bed, but that's not true. Mine has two lights, one on each side. I don't see much downside to the carbon bed other than cost.

FYI, I ordered the rubber bed mat for the CarbonPro to keep things sliding from sliding around. There is a different part for the CarbonPro mat. Bed Mat in Black with GMC Logo for Short Bed (for models with CarbonPro Bed) Part No. 84635351 MSRP: $155.00*

Got mine a few days ago and put a couple hundred miles on it over the weekend. Absolutely love the motor! Great power, quiet, smooth and great MPG. It pairs really well with the 10-speed. Reminds me a lot of a Duramax Allison combo in how it shifts. I've noticed a lot of computer control going on. You can hear clicks and servos starting whenever you open a door. I'm used to this with DI gas engines where opening the door will prime the high pressure fuel system. I assume the same thing here and also probably the DEF system. I think this has some wicked ECU management going on. The coolant temp seems to be tightly managed. I noticed at times the temp staying well under 210, then going up to 210, then over 210 (maybe 220 or 230 according to the gauge) then back down again. It seems to be monitoring engine load and probably lots of other things to keep engine temp optimal for efficiency. Very different than a simple thermostat opening at set temp. Also, the active grill shutters are probably being used to help regulate coolant temp for max engine efficiency and aero drag. This is not an engine I would dare tamper with (tune, etc) for a long long time. I'm not sure it has done a DPF regen yet. If it did, it was less than 10 minutes. The only weird thing I've noticed is the DEF gauge showed one bar under full when I took delivery, then showed about half a tank after 50 miles or so, then popped up a notice that DEF range was 986 miles or something close to that. I added 2.5 gallons DEF today and it took all of it. I bet the dealer didn't fill the DEF tank and it prob had whatever it came out of the factory in it, and prob not enough run time for the DEF gauge to measure the actual amount (hence it showing nearly full). The truck had like 9 miles on it when I took delivery. No harm, I'll add DEF until it's full and go from there. My fuel gauge shows about 3/4 full now and I've gone 220 miles - no complaints there! My only real complaint so far is the auto-stop system. I just haven't created the habit of hitting the disable button yet, so it will shut off and then I'll remember to hit the button. I love the truck so far, very very happy with the 3.0.

Got my 20 AT4 CarbonPro Duramax in satin steel. Sharp truck and I love the 3.0 so far.

Those look great! Good looking truck. How do you like it overall? Anything you'd change?

Thanks for the opinion. That's pretty much what I thought after I test drove one with the Duratracs. I love the look, but they are a little noisy. I figure for my use which is majority on pavement the 20s make more sense. How do you like the truck? Anything you'd change? Do you need a rubber bed mat with the carbon bed to keep things from sliding around?

I've got a 2020 CarbonPro AT4 with 3.0 diesel on order. Have it pretty well loaded. Decided on Satin Steel metallic since it is more of a dark gray than silver color. Considered white and black, but with the blacked out trim that comes on the CarbonPro I thought it had too much contrast with white and not enough with black. They all look pretty good though. A couple minor things I'm still undecided though (order just went in and hasn't been picked up yet so I can still change it). I ordered the factory mud flaps, but not sure if they are worth it. Do most of you have the factory mud flaps? Are they big enough to do anything on the lifted AT4? How do they look? All the trucks I've looked at in person don't have them. I also ordered the 20" carbon grey wheels that are available with the CarbonPro package. I love the way the 18 inch AT4 wheels with beefy Duratracs look, but I think they are too noisy for my use. The ones I test drove were noisy at low speed. I don't intend to do any heavy offroad work, worst case would probably be some muddy or rutted logging roads and snow, but 90% of driving will probably be on pavement so the 20" with quieter tires seem like a better choice. I like the carbon grey wheels too. When I see the beefy Duratracs though I get some second thoughts. Think skipping the 18" Duratracs on an AT4 is a mistake? Now I'm curious how long it may take to get built and delivered. I'm guessing 8 to 12 weeks, but who knows.

I don't work for Motorola, but have studied quality a bit. I don't work directly in automotive, but am close to some people that do. I know enough about component build to think that out of spec components could be a big part of this problem. Sometimes, two or three levels into a supply chain, part manufacturing QC isn't the best. I agree with you that the next gen truck will very likely have this vibration problem resolved. I heard that the new trucks that were shown at some recent dealer conferences look really good and there are apparently some really innovative features. We will see!

The torque number was posted in this thread somewhere, I think it was 90 ft-lbs but you should check that first. RFB = road force balance. My tires were not badly out of balance but enough to contribute to the problem. Like I said, on that 15 those two things cleared it up and it was 99% smooth. My 17 has not had any vibrations at all. As has been discussed here at length, the likely scenario is that the frame is so stiff that certain vibrations resonate in the frame, at certain frequencies. Apparently, there are many things that can setup the 'frame beaming' resonance. Wheels out of balance, axles, driveshafts, transmission components, basically any rotating element that is out of balance/round enough to create an energy wave that then begins to resonate in the frame. That's why RFB works for some people and not others, or new tires, or new axles, etc. Also explains why there is no fix from GM - there isn't a single thing they can do to fix it. They can and do troubleshoot common triggers but the source may be different from one truck to the next. Many trucks don't have the problem at all.

I agree with this. If every post on every page of this thread was a new, distinct person with a vibration problem, it would only represent something like .003% of trucks sold. And we know much of this thread is information, not actual new people with the problem. There clearly is a problem but it is not as prevalent as this focused problem discussion may make it seem. My 15 double cab had the vibration which was resolved with tightening the stock leaf U bolts and a good RFB. My 17 is smooth as glass and the best truck I've owned so far. I wonder if GM made some small changes, or perhaps improvements in quality control for key parts like axles, diffs, gears, wheels, etc to reduce the likelihood of a vibration in the 17s. It is possible that earlier years parts were not being manufactured to meet all required specs (small deviations that may have passed QC or testing, but still enough to cause a vibration). GM may have smacked their vendors and tightened up QC and/or actual tolerances/specs. Who knows - purely speculation, but the problem seems to be less on the 17s. In fact, this thread has slowed down quite a bit recently and there are relatively few 17s reporting in here versus earlier years.

I had a 15 double cab 4x4 SLE that had the shake but that I was able to get resolved by tightening the factory U-bolts and a good RFB. Now I have a 17 crew cab, 4x4 Z71, SLT that is smooth as glass at all speeds. Only 1500 miles but fingers crossed it holds up. My 15 had the shake by now. The thing I don't understand is why some trucks have it and some don't. GM sells nearly 700,000 of these trucks every year. Maybe 2 million since MY14? That's a big number, and even though this thread has 738 pages, it doesn't represent all these trucks. If it is frame stiffness, like a vibrating tuning fork, then maybe some just don't have enough out of balance components to set off a vibration.