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PIP5480A - Chugging, Stumble, Harsh Tip- In/Tip-Out

12K views 18 replies 11 participants last post by  UTEngineer 
#1 ·
Attached is a GM technical document regarding the 2017 L5P advising the technician of the repair procedure.

I have the same issue with my 2019.

Impatiently waiting on GM to come out with the updated firmware for the 2019 models.
 

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#2 ·
Isn't that the stuff that was rolled into the recall on 2017 's and early 2018's and implemented from the factory late Oct 2017 for 2018 models built then or later?
 
#3 · (Edited)
Howdy. I believe you are correct on the recall for 2017’s and early 2018’s ... but my truck is proof they still have the same, or similar, issue going forward into the 2019 models. Was afraid my truck was an anomaly with this issue, but my dealer made me aware they have experienced many 2019’s being brought back to the service department with this issue. Should have asked the dealer about 2018 models.

Funny part, dealer told me to drive around in tow / haul mode and I would not experience the issue. Tried this and they are correct, yet to experience the issue in tow / haul mode. GM still needs to fix the actual problem because driving around in tow / Haul mode is a bandaid, not a solution.
 
#5 ·
Got my call back from GM customer service this morning after my stern email to them last week.

Same story, “we are aware of the issue but GM has not released a fix for the problem at this time”.

Requested an update of when we can expect a fix release ... response was “we have no timeline available at this time”.

Frustrating part is “they are aware of the issue” ... and they obviously do not feel committing to a fix timeline is the right thing to do for affected customers.

Thankfully the truck is drivable ... and this issue has not caused me any dangerous situations.

But it does bring up the question ... if this issue was something critical that impaired the vehicle from being driven ... would you receive the same response that there is no timeline for a fix at this time?
 
#6 ·
Well, going on the fifth model year of production the shudder issue with the 8L45/8L90 series of 8 speed automatic transmissions is still an issue. GM just came out with fluid number three (another revision of the earlier revision of "special" Mobil ATF) with the current claim that water contamination due to hygroscopic fluid is the cause of shudder.

I have little faith in their latest magic mouse milk and I have lost track of the number of TSBs that have been issued for this transmission which is used for numerous models across the GM product range including the light duty pickups. There is a growing class action suit over the 8L45/8L90 so that MIGHT result in them more seriously looking at the issue but GM tends to put off little customer/product crises until they turn into major crises.
 
#8 ·
I think they might have learned a valuable lesson with the 8L series. It was built with a "squashed" torque converter so that it would fit in the same space as the prior 6L series and the converter lockup clutch apparently isn't sufficiently robust to stand up to its environment. The 8L family is especially problematic when paired with engines that use AFM (active fuel management where the engine runs on a reduced number of cylinders). The lockup clutch is continuously modulated under these conditions and it generally causes shudder to appear very quickly.

I know nothing specific about the 10 speed Allison variant coming in the new HD line but Ford took design lead on the 10 speed used for cars, SUVs, and light pickups and it doesn't seem to have any shudder issue. That 10 speed didn't face the same size constraint as the 8 speed and hopefully no equally dumb decisions/constraints were forced on the new replacement for the Allison 1000 series but I don't think I would want the first year of this new transmission.
 
#13 ·
My 2018 and my 2019 have both done this. I have no MIL's though. Talked to the dealer today and he said he thinks the 2019's have a problem with the Throttle Position Sensor and he's going to check it next week. There are times when it's worse than others and I put it in Tow/Haul mode just for the relief. Several times the transmission has down shifted so hard (both 2018/2019) models I swear someone rear ended me. Or it shifts so hard I my u-joints are broken. I never had any of these problems in my 2012 or 2015. I haven't been on the Ford forums but the grass sure is looking greener on the other side. I fell off the Ford bandwagon after my 2004 6.0L fiasco. I can't bring myself to by a Dodge...The definition of "dodge" in the dictionary is "to avoid an encounter with"...:)
 
#15 ·
Nothing yet from GM regarding this widely reported issue.

Not holding my breath that GM will ever fix this problem, especially if the cost to fix the issue is too high.

With the recent strike costs and higher priority recalls on other vehicles, probably take a class-action lawsuit to get GM’s attention once again regarding this issue.

Wish I had better news to offer.

I found this issue only occurs while lightly depressing the accelerator pedal.

Using tow/haul mode and avoiding lightly depressing the accelerator seems to all but eliminate the issue ... for the most part.

However, I do have this long gradual downhill road into town where my truck requires lightly depressing the accelerator pedal to maintain the speed limit and the flow of traffic.

The “chugging / stumble” issue occurs with & without tow haul mode engaged on this downhill unless I manually downshift the truck to keep the rpm’s up.

Sad that we have to engage tow/haul mode and/or change our driving habits to deal with this type of issue on a new $70k truck.

Will update this thread if I hear anything more from GM on this issue.

Appreciate if others will do the same.

For now ... drive it like a race truck to avoid this issue :wink2:
 
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#17 ·
https://gm-techlink.com/?p=10589

Transmission Torque Request Override

With 445 horsepower and 910 lb.-ft. of torque, the new engine has increased horsepower and torque compared to the previous diesel engine. After slowing down and then pressing on the accelerator or when changing gears (such as when plowing snow), a short delay in response may be noticed. This delay is designed to help protect the drivetrain from a sudden torque increase. The Transmission Control Module (TCM) overrides the torque request from the driver via the accelerator pedal in order to control engine torque to a level that protects the transmission hardware when making a gear change.

The request override may be noticed most often when a 6th-to-4th gear downshift occurs when applying the accelerator at 70% or greater between 45 and 55 mph (72 and 88 km/h) or when applying the accelerator after a moderate to aggressive braking maneuver from 20-30 mph (32-48 km/h) down to 0-10 mph (0-16 km/h) where a 3rd-to-1st gear downshift occurs.



Transmission Adapt Learns

On a vehicle with relatively low miles, or with low miles since the TCM was reprogrammed, the transmission may seem to shift hard or the engine may seem to flair between shifts. There also may be bumps or jerks when the vehicle downshifts. If this condition is found, it may be necessary to perform a transmission shift adapt quick learn using GDS2.



Change in Torque Converter Lock-up Strategy

In the new 6-speed transmission, the torque converter now locks in 3rd gear instead of 5th gear. As a result, the vehicle will feel more responsive when accelerating from 3rd gear and higher and transmission downshifts may be more noticeable.

On very light accelerator pedal applications when the torque converter is locked, a hesitation, shutter, or stumble may be felt. This feeling is a result of the very high torque the Duramax is capable of producing at low engine speeds as well as the engine being directly coupled to the rear drive wheels. When the torque converter clutch is not locked, it can serve as a viscous damper between the engine and rear drive tires. When the torque converter clutch is locked, 100% of the rapidly increasing torque is delivered to the rear tires.
 
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