2020 Trail boss DFM shudder

Therealnpp · April 15, 2020

Just wondering if anyone else has had this problem. I have a 2020 TB LT with the 5.3 and 10 speed and I keep getting a really bad shudder at low speeds. Specifically 27-40mph (sometimes higher) when I'm steady state driving and just begin to tip into the throttle. It's at the dealer now and they have confirmed and are firing an ECM at it, but I'm always skeptical about ECM "fixes"

Hoping other people can chime in with similar problems or no problems. I'm hoping this isn't just poor design and something can actually be fixed.

topgear1224 · April 17, 2020

Just wondering if anyone else has had this problem. I have a 2020 TB LT with the 5.3 and 10 speed and I keep getting a really bad shudder at low speeds. Specifically 27-40mph (sometimes higher) when I'm steady state driving and just begin to tip into the throttle. It's at the dealer now and they have confirmed and are firing an ECM at it, but I'm always skeptical about ECM "fixes"

Hoping other people can chime in with similar problems or no problems. I'm hoping this isn't just poor design and something can actually be fixed.

It's likley the DFM. On the new trucks GM is pushed dfm literally to the limits as far as how long it stays with deactivated cylinders under heavier loads. It also will round robin which cylinders it wants to fire. It feels like a strong misfire in certain situations.

If it is REALLY bad could be the trans mount issue. Basically under low speed high torque the drive shaft actually begins to lift up the rear of the transmission which makes the u-joints shudder.

Does it still happen in 4-hi?

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Therealnpp · April 17, 2020

The dealer confirmed it was DFM. It's there now and I never checked 4-high. The shudder changes in sport mode and trailering mode. Which leads me to believe (as well as the tech at the dealer) that the DFM is activating when it shouldn't be.

We'll see what happens. It doesnt shudder under high load. It shudders with next to no load. It's def not the Ujoints.

topgear1224 · April 17, 2020

The dealer confirmed it was DFM. It's there now and I never checked 4-high. The shudder changes in sport mode and trailering mode. Which leads me to believe (as well as the tech at the dealer) that the DFM is activating when it shouldn't be.

We'll see what happens. It doesnt shudder under high load. It shudders with next to no load. It's def not the Ujoints.

Dfm does not care about driving mode it will activate in sport mode and it will activate in tow haul mode. Your dealertech is blowing smoke at you. (the algorithms are different for how it activates and how it behaves in those modes but it does still dynamically manage the fuel.)

But let them go ahead and replace the ECU maybe he saw some other things. the scary part is normally if he's looking at a bunch of values that seem crazy and he thinks it's an ECU it's probably not the ECU those are probably the real values.

All I can say is when you get it back make sure you don't have an RPM dependant vibration. use L mode to bring her up to high RPMs in 3rd (probably need to be on the highway) don't floor it as It will unlock the torque converter just work her up there at about 1/2 throttle. if you're getting violent vibrations it's the internals of the motor.

just so you know if you lift off the gas and then put it back in drive after being at high RPMs it's going to like lurch and slam. I found the easy way to smooth out is to keep your throttle at about 1/4 and then go from L to D you're still going to get a little bit of a firm shift but it'll settle out and once it settles out you don't have to worry about it shifting hard.

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topgear1224 · April 17, 2020

The dealer confirmed it was DFM. It's there now and I never checked 4-high. The shudder changes in sport mode and trailering mode. Which leads me to believe (as well as the tech at the dealer) that the DFM is activating when it shouldn't be.

We'll see what happens. It doesnt shudder under high load. It shudders with next to no load. It's def not the Ujoints.

I should probably clarify at low RPMs the engine is effectively "mini-lugging" for efficiency. It is actually making a good amount of torque and that's where it's most efficient. that's why everybody says the lower your RPMs are the better fuel mileage that you'll get. (Assuming you can hold it without pinging) For instance on my 3 liter diesel at 60 miles an hour in 9th gear on a flat road it's generating approximately 180 to 190 lb-ft of torque according to the ecm.

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Therealnpp · April 17, 2020

In regards to the DFM and different modes, I'm aware. What I am saying is the speed and time at which it shudders changes. The shudder is exact at certain moments when the DFM is functioning but the shudder moves to different speeds based in the mode I'm in because the transmission shifts are now different. The DFM in these trucks is pulse width modulated through the use of the torgue converter. My initial thought was the TC was locking up at slow speeds, but according to the technician, the transmission was working the way it should. He effectively noted that the shudder was happening at the same time the DFM was activating.

Yes, I'm skeptical of the ECM because they rarely fix anything, but they have in the past. So, we'll see. It's at least a starting point.

But based on the number of views this post has had, it doesn't appear that there are many people who are having similar experiences, which leads me to believe it can be fixed.

There is also a TSB out for exactly what I am experiencing.

I also want to add that the torque put out through a diesel will be vastly different than a gas engine. My concern is very specifically occuring right at 27mph when I am not on the throttle and just barely tip back into the throttle. Which also leads me to believe that the truck is in DFM mode and is not properly coming out of DFM mode.

I appreciate your feedback, though. Thank you for taking the time to respond.

topgear1224 · April 17, 2020

In regards to the DFM and different modes, I'm aware. What I am saying is the speed and time at which it shudders changes. The shudder is exact at certain moments when the DFM is functioning but the shudder moves to different speeds based in the mode I'm in because the transmission shifts are now different. The DFM in these trucks is pulse width modulated through the use of the torgue converter. My initial thought was the TC was locking up at slow speeds, but according to the technician, the transmission was working the way it should. He effectively noted that the shudder was happening at the same time the DFM was activating.

Yes, I'm skeptical of the ECM because they rarely fix anything, but they have in the past. So, we'll see. It's at least a starting point.

But based on the number of views this post has had, it doesn't appear that there are many people who are having similar experiences, which leads me to believe it can be fixed.

There is also a TSB out for exactly what I am experiencing.

I also want to add that the torque put out through a diesel will be vastly different than a gas engine. My concern is very specifically occuring right at 27mph when I am not on the throttle and just barely tip back into the throttle. Which also leads me to believe that the truck is in DFM mode and is not properly coming out of DFM mode.

I appreciate your feedback, though. Thank you for taking the time to respond.

It can accelerate with clyinders deactivated via DFM. The TCC should be locked under light loads for efficiency. Otherwise it's just spinning the converter. They put a damper in it to quell the vibrations from the clyinders management. Going from no throttle should unlock momentarily, them pwm locked over approx 1.5 seconds.The 19 LTZ I had for a short while had a 2500rpm brake stall....pretty high for stock.

Tracking boost vs NA as far as torque, was just an example.

I know they had a TSB for the trans mount too. I "returned" my LTZ 5.3 because I didn't like how the engine behaved with DFM. Wouldn't be as bad with a 3.42, or in the 6.2 but they had neither. So I had to take the LM2 or deal with the poor 5.3 top end performance.

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Therealnpp · April 17, 2020

Aside from this shudder, I love everything about the truck. Hopefully they can fix it, whatever it ends up being.

Thanks again

GMCustomerService · May 6, 2020

Hi, therealnpp. Was the dealership able to resolve your concerns? If not, we are happy to reach out to them to provide an additional layer of support. To do so, please send an email to [email protected] ATTN:therealnpp/GM Trucks with your contact information, VIN, brief description of your concern, and preferred dealership. We look forward to hearing from you. To learn more about GM's privacy policy, please visit http://bit.ly/2h3ZUnC.

Aleigha W.

bh069me1 · October 4, 2020

On 4/17/2020 at 12:11 PM, topgear1224 said:

It's likley the DFM. On the new trucks GM is pushed dfm literally to the limits as far as how long it stays with deactivated cylinders under heavier loads. It also will round robin which cylinders it wants to fire. It feels like a strong misfire in certain situations.

If it is REALLY bad could be the trans mount issue. Basically under low speed high torque the drive shaft actually begins to lift up the rear of the transmission which makes the u-joints shudder.

Does it still happen in 4-hi?

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I'm having this same issue...can you give a tsb number or link for the trans mount issue...and can op give clarification on whether his issue was fixed by the ecm replacement?

Thanks.

SilveradoTB217 · December 21, 2020

On 4/15/2020 at 3:52 PM, Therealnpp said:

Just wondering if anyone else has had this problem. I have a 2020 TB LT with the 5.3 and 10 speed and I keep getting a really bad shudder at low speeds. Specifically 27-40mph (sometimes higher) when I'm steady state driving and just begin to tip into the throttle. It's at the dealer now and they have confirmed and are firing an ECM at it, but I'm always skeptical about ECM "fixes"

Hoping other people can chime in with similar problems or no problems. I'm hoping this isn't just poor design and something can actually be fixed.

I'm having this exact same issue in my 2020 Trailboss with the 5.3. The shudder happens after the truck is in top gear and DFM is activated, then you apply very light tip of the throttle and it feels like you just drove over a section of rumble strips until the truck drops to a lower gear. My truck is going back to the dealer tomorrow. I had it at the dealer for the last 2 weeks and they replaced the torque converter. After I picked it up this past Friday, I got a mile down the road and the issue still occurred. I've got 18k miles on my truck and it didn't start getting bad until about 15k. Now I have what seems to be a driveline vibration that's stemming from the DFM acting up.
Can you give me an update on what the dealer ended up doing on your truck? I'm going back to my dealer tomorrow morning.

Therealnpp · December 21, 2020

25 minutes ago, SilveradoTB217 said:

I'm having this exact same issue in my 2020 Trailboss with the 5.3. The shudder happens after the truck is in top gear and DFM is activated, then you apply very light tip of the throttle and it feels like you just drove over a section of rumble strips until the truck drops to a lower gear. My truck is going back to the dealer tomorrow. I had it at the dealer for the last 2 weeks and they replaced the torque converter. After I picked it up this past Friday, I got a mile down the road and the issue still occurred. I've got 18k miles on my truck and it didn't start getting bad until about 15k. Now I have what seems to be a driveline vibration that's stemming from the DFM acting up.
Can you give me an update on what the dealer ended up doing on your truck? I'm going back to my dealer tomorrow morning.

The dealer replaced the valve body in the transmission. I’ve got 5100 miles on it now and it has been great ever since.

SilveradoTB217 · December 21, 2020

24 minutes ago, Therealnpp said:

The dealer replaced the valve body in the transmission. I’ve got 5100 miles on it now and it has been great ever since.

Good deal. I'm hoping and assuming that's what my truck is doing b/c your initial post described mine to a T! I love the truck but this issue has been aggravating after coming from a 2017 Silverado with the "chevy shake" issue. Thanks for the response and I will update after my dealer visit.

lothodon · December 30, 2020

I'll chime in, long history...

2015 Silverado, shake, tried a LOT with full dealer support, tires, wheels, driveshaft, thankfully dealer damaged my truck so it was easy to part with.

2016 RAM, 4/8 cylinder mode sucked on their attempt too. Tuned with DiabloSport Intune I3 (and unlocked computer $$$) dealer did update and relocked computer, never should have bought this one.

2017 Silverado, same tuner disabled AFM YAY! Never should have SOLD this one!

2017 RAM, still no better and shook. Manually shifted into 8th to prevent it from enabling. HUGE mistake.

I REALLY HATE reduced cylinder modes.

2019 TB, yup still hate it even being DFM (upgraded AFM), DiabloSport Pulsar LT arrived TODAY, no more auto start/stop or DFM, also fixed my speedo and tuned my throttle response. WORTH EVERY PENNY!

This trend I'm afraid will never go away and it's just not a good system no matter how many tries they throw at it.

14SLE · December 31, 2020

My '20 Sierra SLT has the occasional shudder at low speeds--I particularly notice it in a school zone on the way to work. It appears to be a resonance that occurs at a specific RPM and/or speed combination with DFM active. However, giving it a bit of gas pedal clears it up quickly, so I have to say it is WAAAYYYYYY better than the old nightmare that was AFM (lurch, chug, lurch, chug). You can probably eliminate the shudder with a Range Technology AFM/DFM disabler if you cannot live with it and don't want to risk your warranty. I had a Range unit for my old truck that is on its way in for an update to the newest version right now. I will be curious to see how it works on the '20 truck and what effect it has on fuel economy. I probably won't use it much unless the DFM system gets more obnoxious over time.