Hard Downshift on Diesel 21 Yukon

[jasonk_]

Recently purchased a 21 LM2 Yukon, 7 miles when I accepted delivery. Currently at 1200 miles.

Around 100 miles ago, I started noticing a significant shutter/hard downshift during braking/deceleration around the transition from 28mph down to 22mph. As I’ve experienced it more, it begins to happen when the transmission is at 160 degrees and is most noticeable when the transmission is at 180 degrees and up. In any of the 1000-1100 miles before, the truck has never exhibited this. No other issues really other than the occasional mild jolt when reverse is engaged.

I have an appointment scheduled at an area dealer but wanted to reach out and see if anyone else has had this on the LM2/10 speed combo.

 

[txchevy4ever]

I noticed this while it was in the DPF regen cycle mode. Manual says it's normal, but I would definitely not describe mine as "significant" only a very mild change in exhaust note.

 

[Holy Roller]

I have experienced the same hard downshift while breaking or on coast-down when the Diesel engine is in regen.

 

[jasonk_]

I have experienced the same hard downshift while breaking or on coast-down when the Diesel engine is in regen.

At first I thought it was Regen related but it continued after a 40 minute highway drive and it was clear I was outside of regen (idle normal, no change in exhaust/throttle response) and it continued the next day.

 

[txchevy4ever]

At first I thought it was Regen related but it continued after a 40 minute highway drive and it was clear I was outside of regen (idle normal, no change in exhaust/throttle response) and it continued the next day.

Let us know what the dealer says.

 

[jasonk_]

Update: The hard shifting stopped approximated 1 day after the above post and has remained smooth since. I also took the vehicle to my local GMC dealer and they were unable to find any codes\issues with the truck or the transmission.

They did note that TSB 16-NA-019 applies to this transmission and allow for 5000 miles before performing and repair\reprogramming.

I'll update the thread if condition warrant.

 

[100cars]

Just chiming in - I had a regen event yesterday and did not notice any difference in shifting. I am at about 1200 miles.

 

[Stbentoak]

Is there any obvious way you know you are in “Regen” with these vehicles? When my jeep was in active regeneration it would pop up an indicator and say keep driving till it finished and disappeared….

 

[100cars]

Is there any obvious way you know you are in “Regen” with these vehicles? When my jeep was in active regeneration it would pop up an indicator and say keep driving till it finished and disappeared….

There is a very distinct difference in exhaust sound under very light throttle. It's almost boomy.