“Service transmission Now, unable to shift soon” message on 2021 Tahoe

[West1]

That is garbage.
All the modules store history codes..they could at least look.
Next time take a picture or a video of the code on the screen...harder to argue w/ evidence.
These dealers are really starting to tick me off...

I did take a picture and a video.
This morning it happened again and I drove to the dealer and kept the engine running. They scanned it and said there’s a ton of codes popping up with a low battery voltage. They said start with replacing the battery and go from there.

I also asked if I could swap the battery myself (since not a lot of people on the forum know the solid answer) and they said yes, no problem swapping batteries.

Off to buy a battery…

 

[WalleyeMikeIII]

I did take a picture and a video.
This morning it happened again and I drove to the dealer and kept the engine running. They scanned it and said there’s a ton of codes popping up with a low battery voltage. They said start with replacing the battery and go from there.

I also asked if I could swap the battery myself (since not a lot of people on the forum know the solid answer) and they said yes, no problem swapping batteries.

Off to buy a battery…

FYI, Low Voltage has also been caused in GM vehicles by corroded frame ground wires...so, make sure you/they inspect those bonding braids. (I will never understand why GM thought bare copper braid for frame ground in a corrosive environment was a good idea). This video is worth a watch.

 

[Fless]

FYI, Low Voltage has also been caused in GM vehicles by corroded frame ground wires...so, make sure you/they inspect those bonding braids. (I will never understand why GM thought bare copper braid for frame ground in a corrosive environment was a good idea). This video is worth a watch.

After having watched that video a few weeks ago, I wondered if the SUVs have that same ground cable.

 

[Doubeleive]

After having watched that video a few weeks ago, I wondered if the SUVs have that same ground cable.

not only that but the idiots put the ground cables right where all the water splashes up from the wheels
job security I guess, some engineer needs a smack upside the skull

 

[West1]

Update… my battery was the issue.
I swapped it out (scared af after reading on our bus bars & ECM stuff) and have no issues atm!

(Can’t load pic, says file is to big).
I was worried disconnecting the positive wire would cause ECM issues but… I was the test. There’s a small bar near the negative terminal that needed to be removed, a clip with a red tab and a clip on the bus bar housing that holds it on the battery.
After this, there’s a big bolt at the bottom back corner of the positive terminal that unlocks the physical battery. Once that’s done, it’s easy to loosen and remove the battery.

I figured I’d mention this since there seems to be little info on people removing the battery on our rigs.

 

[Tahoe14]

You do have to be careful with these new rigs changing batteries. One little spark and it can throw a code that the Dealer has to clear. Unhooking the negative battery cable does not always work.

 

[StephenPT]

After having watched that video a few weeks ago, I wondered if the SUVs have that same ground cable.

Nope - '21+ SUVs use a cable with sealed heat shrink ends and wrapped in Tesa tape. Pretty weather proof in my book. I saw the SMA video when it came out and removed by fender liner to check.

Part number # 84871178

 

[Doubeleive]

Nope - '21+ SUVs use a cable with sealed heat shrink ends and wrapped in Tesa tape. Pretty weather proof in my book. I saw the SMA video when it came out and removed by fender liner to check.

Part number # 84871178

View attachment 438607

different platform with the T2's, not even the same at all

 

[Staceyr72]

I'm so curious to how many 2021 Tahoes are having this issue?
I have a high country, 2021, my dealership has had it for over 2 months, can't get the part to fix it - valve body-
They have another one there, that's been there for 5 months, can't get the part.
So, 2 Tahoes at same dealership, same problem, and can't get the part to fix.
I have escalated to chevy, have a case number, chevy themselves can't get the part to fix my truck. But I still have to pay for it-big payment for something, I can't drive, isn't worth anything for trade and useless- I am furious. I have been a lifetime chevy owner-and this is changing my mind.

Last nights communication with chevy escalation please read:
Dear STACEY,

We have the following update for your 2021 Chevrolet Tahoe, case number 9-14734770575.

We are still experiencing a delay on the part(s) needed to repair your 2021 Chevrolet Tahoe. We understand this is a significant inconvenience and we continue to work diligently to resolve the delay. If further information is made available, you will be contacted by your dealer or myself. Thank you again for your patience and please contact me to discuss any additional questions or concerns you may have.

I can be reached at the number listed below or emailed at [email protected] (please reply with history to this email for fastest response).

AND MY RESPONSE:

​

Thank you for the update.
However Janet, if you can not find the part. I want my truck fixed asap. If that means a new transmission then that means a new transmission. This is a Chevy problem and Chevy knows it. Otherwise, payoff my truck. Give me full value so I can trade it I owe $54k.
Not to be a complete rude person. But if my truck doesn’t get fixed fast. I’m going to start escalating this to who ever will listen
I know this isn’t your fault. But it’s not mine either. And I have a $1300 a month payment for something I can’t drive. And Chevy can’t fix!

 

[Tahoe14]

At the least they should be paying your monthly truck payment and providing a rental and I would be asking for an extended warranty for the inconvenience. Get an attorney and as part of the settlement they pay your attorneys fee. Good luck and I hope you get it worked out.

 

[BigE_In_TX]

Well, I found this thread because I got the message today. After work I drove straight to the dealer and they did not see the message. They basically told me with no code, they can’t do anything.
I left and about 3hrs later and roughly 6 drives later, I got it again but for only a moment. The message turned off within a minute.
2021 RST @49,300miles


Any update on your end OP?

@West 1 Hey sorry for just seeing your question. I never got a true story to what caused this so got rid of the SOB! First year of the redesign, never do that again. This was particularly my wife’s, so I couldn’t risk her being stranded, and like I said, she was 3,000 miles out of warranty, so it went bye bye.

 

[West 1]

Sorry but that question was not from me?

 

[BigE_In_TX]

Sorry but that question was not from me?

I quoted you, just replying to your comment

 

[the 18th letter]

I quoted you, just replying to your comment

@West1 and @West 1 are different users.

 

[BigE_In_TX]

Gotcha sorry

 

[SSGUNNER]

Hi folks, haven’t been here in a while and yes, sorry for reviving this from the dead. But guess what…

Today I got this stupid message while I was going to the gym. Went straight to dealer and they did a a scan and woohoo got some codes. The first one was a low voltage and 3 others can’t recall since I’m back home waiting. My ride is currently at 67650 ish so waiting to see if it is indeed the battery or not. I’ll keep you posted.

 

[BigE_In_TX]

Hi folks, haven’t been here in a while and yes, sorry for reviving this from the dead. But guess what…

Today I got this stupid message while I was going to the gym. Went straight to dealer and they did a a scan and woohoo got some codes. The first one was a low voltage and 3 others can’t recall since I’m back home waiting. My ride is currently at 67650 ish so waiting to see if it is indeed the battery or not. I’ll keep you posted.

@SSGUNNER Thank you for reviving this thread from the dead, people need to know because at this point in 2026, unless your purchased a 2021 certified pre-owned, warranty is looong over! It could be a completely different scenario now, but at the time, the stealership did not know a fix and were keeping the Tahoe for weeks/months. I personally said F it and got rid of my 2021 that was throwing these codes, so didn’t stick around to see if there was a “fix”/ solve for this.

I was reading a motortrend article about 7-8 months ago, and it was about the 2021 Tahoe specifically. The article stated that Chevy admitted that the production was rushed to get to market and the 2021 model year for the Tahoe are much less reliable because of that. Maybe because of COVID? I remember purchasing mine in July 2020, which is much earlier than you typically see the new models hit dealership lots.

Anyways, good luck and hope you can get piece of mind. Thank you for posting here. Please pass along your experience to hopefully help others in this same predicament.

 

[BigE_In_TX]

@SSGUNNER OH also here is another thread discussing this same issue. What is quite humorous to me is the very last post. Guy says while at the dealership be diagnosed for this transmission error, he gets an onstar e-mail saying his battery was low. He calls the dealership to tell them to replace the battery while they have it, and voila, problem fully fixed……

2021 Tahoe Premier Transmission

Hello, I have a 2021 Tahoe Premier with 30,500 miles on it. Yesterday, all of a sudden I received the error, "service transmission now, unable to shift soon" I called my dealer, and of course they are swamped, but agreed to take it in as an emergency. Any idea what this is about? I googled...

www.tahoeyukonforum.com

 

[SSGUNNER]

Update:
So I got a call from the dealer and said it was the transmission control module, also the battery was producing 300 instead of the 700 a newer battery does and my front brakes are extremely low at 14% life. Which I didn’t even take it in for. Researching a bit more before I call them back and tell them to F off. $1200 for the transmission module.

 

[jfoj]

I condemn my batteries when they test at 75-80% of rated capacity. Your battery is less than 50% of rated capacity it is LONG overdue for replacement. Weak batteries cause low voltage dips during cranking which will cause multiple modules in the vehicle to fail the properly communicate and cause all kinds of strange behavior. I would not replace the transmission control module. I'd replace the battery and see what happens.