2015 SLT Yukon Xl just purchased V4-V8 mode Shakes

Chris O · February 11, 2015

Just like others my brand new 2015 SLT Yukon Xl is shaking at 1100-1300rpm. Most noticeable at 40mph when it's in v4 mode chugging along, but it can happen at all speeds if your in the v4 mode. Drove back to dealership and had service advisor and shop foreman ride with me and we have a problem. They did a new flash for engine and transmission but that did not resolve anything. Can anyone offer any advice to fix this issue?

GRN69CHV · February 11, 2015

Hello Chris, welcome aboard, I'm a newbie on this site also, but a veteran to trucks and hot rodding. First let me ask, where do you live, is it hilly or relatively flat? Have a 2015 Silverado LT with the same 5.3L, 6 spd trans and 3.08 gearing. Personal opinion, Considering your Yukon SLT XL is right around 6000# with driver, it's too much weight to pull when the motor goes into V4 mode and tries to shift into 6th gear. Have the same issue with my Silverado Double Cab (and my truck is probably 500# less than your Yukon XL). Bottum line, these trucks need more gear and/or reprogramming to keep the trans in a lower gear. As an experiment, I've been running mine around in either M5 which keeps it both out of 6th gear and out of V4 mode - it's silky smooth and runs along nicely in 5th in V8 mode, add to it, from what I can document it gets the same or better mileage in rural driving. The other experiment I've tried is running it in Drive:Tow/Haul mode. Very interesting results doing this, the trans will shift up to 4th or 5th gear as needed and keep the engine rpms in the 1800-2000 range but the motor will run for extended periods in V4 mode. In drive the motor only goes into V4 mode in 6th gear, which from my experience comes as far too low mph and engine rpm. I think these need either deeper gearing or a reprogram to allow V4 mode to activate in 5th gear when in drive and move the 6th gear shift point up to about 50 mph.

Chris O · February 12, 2015

GRN69CHV. Thanks for the info and wow what a differance. The M5 mode is the fix for sure, no fluttering, shakes, vibration or anything silky smooth as you said. Now the question is the MSRP of 68,000, should I just deal with it or make a complaint for something they probably can't fix?

GRN69CHV · February 13, 2015

Chris, (by the way, my name is Joe). Had my truck into the dealer today for something minor, while in I had a chance to talk at length to one of the younger service managers who is more into tuning these. Seems we are all in the same situation. I'm on the fence with getting a handheld tuner to attempt to reprogram the trans shift points along with adjusting the V4 mode (I'd like to see the trans reprogrammed to delay shifting into 6th gear until about 1800 rpm which is roughly 64 mph when in drive). Other thing I am strongly considering is just getting the Range Technology plugin to disable AFM. Reprogrammers (Diablo, Hypertech, etc) are great but I really don't see the point in doing a reprogram of the factory settings for another 10-12 hp at 5500 rpm when all I really want to do is smooth out the low speed operation. Range module doesn't alter factory settings, it just overrides the command to go into V4 mode. I'm probably going to try this first and see how the motor responds to running down the road at low rpms but firing on all 8 cylinders. Other (costly) option is a gear ratio swap, plenty of discussions on this also - again, not sure I an ready to venture down that road if a simple plug/play module will do the trick. Stay tuned, I'll let you know if I get it and how it works.

Chris O · February 14, 2015

Great news, do you think leaving the vehicle in M5 will hurt the vehicle any? I just got the OnStar fixed today so that seems to be working. I still can't get text messaging on my infotainment screen, any ideas on that. Dealer had no clue.

GRN69CHV · February 15, 2015

For comparison, if you run the truck in tow-haul mode, it operates similar. From a mechanical standpoint, keeping it in a lower gear reduces the load on the trans, with the rpm's elevated the pump turns faster and increases fluid flow across the trans cooler. As long as you don't mind selecting the gear shifter It's all good. Option is to get deeper gears to do the same thing - which I have considered, but quite frankly the more I run it in M5 around town it's becoming send nature.

Wrench589 · February 15, 2015

I think they all run a bit rougher in V4 mode. After all, a V4 is inherently rougher then a V8. That said, I think it's only fair that GM, and your dealer, evaluated yours against whatever allowable vibration level GM has defined to ensure there isn't something off-spec with yours. From the few different 2015 SUV's I've driven, V4 mode is noticeably rougher.

I'm with GRN69CHV on altering she patterns or completely disabling V4 mode altogether. In fact, I was browsing for tuners this afternoon for that very reason! Should GM alter the factory program to resolve this? Yes. Will they? Not likely, as there is likely a 1/4 mpg at stake on the EPA test track and the big 3 are in a bit of a marketing battle for who has the best mileage. So, GM need to keep the numbers as low as possible, often at the expense of drivability and comfort.

So, aftermarket tuning starts looking better all the time.

Chris O · February 17, 2015

Thanks for the update I just find it hard to spend more money.

Wrench589 · February 22, 2015

Yea, it's not right that the owners have to make the vehicle right. It's possible that enough owners complain and complain and complain to GM, they will modify the engine computer program so it's not so aggressive with V4 mode and holds V4 at such low rpm, but then mileage will suffer slightly. And, then they will be on the hook for selling vehicles at one EPA rating and then changing them after the fact. So, I suspect GM will be very hesitant to do so.

Now, what will they do for the next model year? Find a way to improve the issue and maintain mileage ratings? Perhaps. Tough for us owners to know. If it's only programming, there is a change GM will make an update available to those customers that complain. Watch for a TSB on it. May take a year to show up, though!

GRN69CHV · February 23, 2015

The more I drive the truck, the less negative I become of the 3.08 gears and do think it's more about programming. Being an old gear head, I go back to comparing how this matches up to running a 4L80E. The 6L80E/3.08 ratio has the same effective 1st gear as a 4L80E with a 4.88-5.13 rear axle ratio. In 5th gear it has the equivalent to a 4L80E in overdrive with a 3.55 gear. For me the issue is strictly at what point the motor drops into that deep .67 overdrive. You can run these in M5 and it gates along nicely in V8 mode, completely staying out of V4 mode. You can also run these in drive/ tow-haul mode and it will go cruise down the road in V4 mode in 4th or 5th gear, not dropping into 6th gear until about 55-60 mph. In full auto, it only goes into V4 in 6th gear at about 35-40 mph. Tells me, it's programmable. I really think all that is needed is a reprogram to allow you to set it in Drive, have the motor to run in V4 mode in 5th gear and delay the drop to 6th gear until about 50-55 mph. For now, I drive mine in either M5 or Drive/Tow-haul mode.

CHRIS.H · September 23, 2015

Chris O. ,

I just bought a 2015 yukon xl slt. with 43k. It has a vibration every time the v4 kicks in, if at very light throttle. Esp up a slight incline. However if at full acceleration the 2-3 shift(67mph) vibrates like crazy. Dealer has no idea. I'm getting it reprogrammed today to remove the v4. I'll update as it goes.