2023 Allison transmission valve assembly

daywright · July 9

16 hours ago, daywright said:

our 3500 2020 Sierra 58000 miles going 55mph on a slight incline, go to press
accelerator and truck makes loud boom feels like a hit a speed bump at 55mph, figure it was trailer since no warnings come on. happens again 3 secs later...pull over and let truck cool try to find some evidence of what the hell just happened. take to dealer they cant replicate, no codes.
happens again at 91000, this time not towing. this time just cruising in traffic no load not trlr. loud bang drop rpm rolls on no problem. get out let trans cool continue down road no issues.
Dealer cant get in for 40 days...no clue. you probably hit a pothole you didnt see.
happens again at 109000, this time rear brakes lock up three times in a row(smoke rolls from under bed each time)skidding for about 6' each time. towing skid steer at 45mph. Cars gotta avoid me this time as speed dropped a lot. pull over to check trans and tires for flat spots. trans running about 203,(nbd) tires are flat spotted, (sucks).
Called dealer and they say a month away to appt.
okay ill check this out. oh theres a tsb from jan 2022 (ABS event for valve body21-na-275).
This is a mfg defect not a wear and tear. this is dangerous and unacceptable.
GM has no parts and it needs a reprogrammed so I cant fix this at home, dealer only and they wanna charge me to "diagnose" their known defect...

Boogieman66 · July 24

On 7/8/2024 at 7:46 PM, daywright said:

our 3500 2020 Sierra 58000 miles going 55mph on a slight incline, go to press
accelerator and truck makes loud boom feels like a hit a speed bump at 55mph, figure it was trailer since no warnings come on. happens again 3 secs later...pull over and let truck cool try to find some evidence of what the hell just happened. take to dealer they cant replicate, no codes.
happens again at 91000, this time not towing. this time just cruising in traffic no load not trlr. loud bang drop rpm rolls on no problem. get out let trans cool continue down road no issues.
Dealer cant get in for 40 days...no clue. you probably hit a pothole you didnt see.
happens again at 109000, this time rear brakes lock up three times in a row(smoke rolls from under bed each time)skidding for about 6' each time. towing skid steer at 45mph. Cars gotta avoid me this time as speed dropped a lot. pull over to check trans and tires for flat spots. trans running about 203,(nbd) tires are flat spotted, (sucks).
Called dealer and they say a month away to appt.
okay ill check this out. oh theres a tsb from jan 2022 (ABS event for valve body21-na-275).
This is a mfg defect not a wear and tear. this is dangerous and unacceptable.
GM has no parts and it needs a reprogrammed so I cant fix this at home, dealer only and they wanna charge me to "diagnose" their known defect...

On 6/25/2024 at 6:50 PM, UWSkier said:

Did you guys notice any erratic or harsh shifting before things went south? I have a gasser with random hard shifts. 95% of the shifts are silky smooth, but occasionally, it's a kick in the behind.

Shifting up. It happened about 3 times on my trip before the fatal blow.

Boogieman66 · July 24

Update to my warranty issue with the transmission. It has been over 5 weeks since I dropped this off at the dealer.

They say they still do not have the part. Very Frustrating. It seems that GM Does not back up their product. Very disappointed in good old GM. I am out a lot of money and time etc.

GMCustomerService · July 25

On 3/24/2024 at 9:52 PM, Lars Ohrstrom said:

I have a 2023 Denali 2500 diesel with the Allison 10 speed transmission with 49000 miles. The other week, while accelerating on the highway, I truck started jerking, check engine light came on and power was reduced. I limped back to the dealer and was told it was a software issue with the fixed. They said to keep it local to try it out but 35 miles later, it happens again. This time they said it the transmission valve assembly. Not a bad thing, all under warranty but now they said the part is back ordered and no idea when it will be in. Reading some other posts and it seems it can be months. A friend helped me and found a unit at a dealer in Scottsdale Arizona which I shared with my service adviser, she said they can’t do that. They are getting me a loaner truck but are not happy that I drive about 4000 miles a month. Any advice on how to proceed or am I stuck in the waiting room? I even offer to buy the part myself, $1100.00 and have them install it but that didn’t get a positve response.

We regret to hear of this transmission concern with your vehicle and would like to investigate further for you. To do so, please send us an email to [email protected]. Be sure to include your Username and Forum name in the subject line with additional details. We look forward to your email.

Jay413 · August 22

2023 2500 with under 25,000 miles with the same problem. Dealership has had the truck for 8 weeks. Valve body is backordered with no date of potential shipment. But yet, they are steadily selling trucks with the same transmission so they isn't a shortage of parts if GMC is steadily assembling these trucks to sell. They care more about there sales than existing customers.

GMCustomerService · August 22

4 hours ago, Jay413 said:

2023 2500 with under 25,000 miles with the same problem. Dealership has had the truck for 8 weeks. Valve body is backordered with no date of potential shipment. But yet, they are steadily selling trucks with the same transmission so they isn't a shortage of parts if GMC is steadily assembling these trucks to sell. They care more about there sales than existing customers.

We are sorry to hear that you are experiencing these concerns with your vehicle, and we understand how part delays can be frustrating. Our team would like to take a moment to learn more and investigate further on our end. Please send us an email to [email protected]. Be sure to include your Username and Forum name in the subject line with additional details. We look forward to your email.

PHDizzleWizzle · August 28

Same issue here. I have a 2023 2500HD with 30k miles. Taking off from a stop light the truck shifted really hard and went into low power mode. Limped home and took it to the dealer, its a valve in the allison tranny that needs replacing. They don't have a clue when the part will be in. It's been since June 17th now that it broke down. They wouldn't give me a loaner, so i had to argue for a rental car. Well I have wheels to get around but the suburban doesn't have any hitch. I pull 5th wheels for work and my camper. Needless to say its messed up my whole summer because of no tow vehicle. They are saying it could be a year..? Pretty ridiculous they you pay all this money for a truck they can't even fix. Got the Covid excuse for part back order... IT'S A DAMN JOKE.

Ben Watercutter · September 6

Same boat. 23 3500 AT4 22k miles. Been at dealer for 5 weeks and counting. No eta. BBB, lemon law attorney, ohio attorney general and Jim Jordan all on the case now. Figure if I raise enough hell maybe gm will wake up. Refused to give a loaner of any sort. Attorney said to expect between 12-20k settlement

Inventor24 · September 9

2023 GMC Sierra Duramax Diesel with 10 speed Allison Transmission with 28,000 miles can't be driven. Currently at the dealership due to a transmission valve body problem, codes P0700 & P0747. While driving I felt a hard shift and the truck jerk. The engine light came on and my truck went into low power mode. Let it sit over night and truck would shift fine. This happened 3 times over a 1 month period. After getting to the Chevy dealer they told me the issue is with he valve body and said they have been having multiple trucks come in with the same problem. They have a truck in there since May (4 months!) They told me there is no ETA for the part. I've read this is a common issue happening on 2023 & 2024 trucks like mine. I've read that the problems have been going on for over 1 year. This is ridiculous for a $90,000.00 truck.GM should be putting new transmissions in or buying the trucks back. I'm considering contacting an attorney to inquire about the lemon law or what other avenues I can take regarding getting the truck fixed, and fixed properly.

Edited September 9 by Inventor24

John Oberheide · September 24

Brought my truck to the dealer 2 weeks ago with the same issue. Truck went into limp mode but after pulling over and turning off and on, it let me drive as normal. check engine light remained on for a day. let it sit over night and started next morning and no CEL. Took it to the dealer and they said valve body needs to be replaced. No idea or clue when it will come in.

Starting to get worried after reading a lot of similar situations where folks have to wait months before parts arrive. Dealer wont provide a pickup truck loaner. Worried I'll be stuck in a chevy cruze for deer season

John Oberheide · September 24

On 3/24/2024 at 8:52 PM, Lars Ohrstrom said:

I have a 2023 Denali 2500 diesel with the Allison 10 speed transmission with 49000 miles. The other week, while accelerating on the highway, I truck started jerking, check engine light came on and power was reduced. I limped back to the dealer and was told it was a software issue with the fixed. They said to keep it local to try it out but 35 miles later, it happens again. This time they said it the transmission valve assembly. Not a bad thing, all under warranty but now they said the part is back ordered and no idea when it will be in. Reading some other posts and it seems it can be months. A friend helped me and found a unit at a dealer in Scottsdale Arizona which I shared with my service adviser, she said they can’t do that. They are getting me a loaner truck but are not happy that I drive about 4000 miles a month. Any advice on how to proceed or am I stuck in the waiting room? I even offer to buy the part myself, $1100.00 and have them install it but that didn’t get a positve response.

Do you still have that part #?

LocoS1 · September 27

Saw this a moment ago:

https://www.youtube.com/watch?v=NvQ3fRX7swQ&ab_channel=FabRats

Dunn · October 2

i just watched a video on YT of a dude replace parts in valve body in the tranny, I guess it was an O ring issue

Scott A · October 24

My work pickup just had this issue. Couldn’t go over 40 mph. Took it in and they said it needed a valve body. They ordered the part and a few days before it was scheduled to be fixed they said they had the parts. Dropped it off a few days early and was using another 2023 Chevy 2500 HD pickup. Same thing happened to this one. I take it in and they confirmed it needs the same part. At 5 pm the day my original pickup was supposed to be fixed I get a call from the dealership and they said they don’t have the part and it’s on national back order! Can’t tell me when the part will be here! So a pickup with 65,000 miles and a pickup with 45,000 have the exact same issue less than 3 weeks apart and the dealership says they don’t have an issue! Then why is there a national back order on them? Sounds like a recall is in order so hopefully more people can get them fixed on their own terms vs the worst possible time. I’m wondering if they gave my part to someone else too. How can they tell me they have it and then tell me they don’t? Either way another poor experience with the same dealership and a GM product. After this experience I don’t see myself owning or recommending a GM vehicle.