2023 Allison transmission valve assembly

Lars Ohrstrom · March 25

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.

gemarsh · March 25

How far are you away from Scottsdale?

Lars Ohrstrom · March 25

I’m in Chicagoland but they can ups it to

me.

NaturallyAspirated · March 25

I’ve switched out a valve assembly before but never on one of these trucks. Anyone here do it on a current Chevy?

Lars Ohrstrom · March 25

Is it a major job to do?

2023 2500hd Denali · March 25

17 hours ago, 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.

Same thing. We just blew out the engine in a 23’ 2500 21,721 miles. Just going down the road. It jerked, idled high and blew out all the oil in the engine. Maintenance on time and everything. No warning signs.

NaturallyAspirated · March 28

Not really a big job:

Drain trans oil.

Remove transmission pan.

Unplug the electronics.

Remove filter.

Remove and replace valve body.

BUT I have no idea how the current Allison is put together. I just did some web searchin and found very little info.

Anyone else on this forum have any information?….

cmj60011 · May 29

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.

Im having the same EXACT issue with my 2023 2500HD High Country with only 30000 miles on it! Although they said mine is caused by the valve body needing to be replaced. It was throwing the code P407/470 something like that....They have had my truck for a month and to begin they refused to give me a loaner, after a lot of hell raising they gave me one and told me not to put many miles on it because it was new.... Well i have a business to run and they are going to have to deal with it unless they want to pay my salary. Its ridiculous to pay $80,000+ for a brand new truck and cant drive it but still having to make the payments. So yes im am going to drive this loaner until the fix the problem.

GMCustomerService · May 29

7 hours ago, cmj60011 said:

Im having the same EXACT issue with my 2023 2500HD High Country with only 30000 miles on it! Although they said mine is caused by the valve body needing to be replaced. It was throwing the code P407/470 something like that....They have had my truck for a month and to begin they refused to give me a loaner, after a lot of hell raising they gave me one and told me not to put many miles on it because it was new.... Well i have a business to run and they are going to have to deal with it unless they want to pay my salary. Its ridiculous to pay $80,000+ for a brand new truck and cant drive it but still having to make the payments. So yes im am going to drive this loaner until the fix the problem.

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Antonio Labella · June 25

I have a 2023 chevy 2500 duramax at 23813 miles ny valve body went bad and the deal has no idea when my part can be in to fix it.... I require a 3/4 ton to tow with and i received a half ton 3.0 duramax dealer allowed me to tow with it. But what they dont realize i guess is that a 24ft enclosed trailer and all the equipment inside ima burn up the transmission in a brand new 63,000$ truck. I was offered 48,000$ for my truck when i put 27,000$ this is beyond a joke GM needs to do better. First Duramax ive ever owned and this happens.

Boogieman66 · June 25

Same thing here. My 3500 has 30,500 miles on it and the valve body needs replacing. Very frustrating because the part is not in stock and I do not know when it will be in. The dealership offered me a rental car but it does not have a hitch. I feel they should give me a 3500 to drive which I need. Apples to apples. is the way I see it.

I was forced to cancel my fishing trip and now I have to cancel my 8 state trip. My entire summer plans have been ruined because a fault in a major component. This should not happen. Ok, I get it, things break. But it is how it is being handled to rectify the situation. Not much communication, no part, they don't know when it will be done, very disappointed in the quality of this truck. The owners of these expensive truck are getting the shaft as it costs all of us more money and time. It seems to me it is not affecting the dealerships or GM in any way as I feel they are not taking our issues seriously. They took our money for the trucks and now they are washing their hands of us.

UWSkier · June 25

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.

Colossus · June 26

17 hours ago, 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.

is it shifting up or down when doing it?

UWSkier · June 26

2 hours ago, Colossus said:

is it shifting up or down when doing it?

shifting up. Happens mostly when accelerating lightly to moderately as it shifts up through the remaining gears once the rate of acceleration is tapering off. I've noticed the occasional clunky downshift coasting or braking to a stop, but less obvious.

daywright · July 9

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...