PLEASE HELP - possible trans issue

[Z71Burban]

Hello everyone,

Very new here and tried searching up this issue but couldn’t really find anything similar so my apologies if this has been covered already.

I have a 2017 Suburban z71 5.3 6speed trans that just rolled over 80k. Literally OVERNIGHT (seriously not 1 single issue before) it seemingly turned into a Ford and does not know how to shift. At 70mph with the cruise set on flat roads, I’m at 3200 rpm in 4th gear. Also, shifting from park to drive, it’s a pretty hard shift but that’s the only hard one. It seems that it just doesn’t know what gear it needs to be in. Also, last night when coming up to a stoplight, it got all confused and just shut down on me. I put it in park and restarted and resumed like normal but something is definitely up. No dash lights or anything. Wondering if it’s maybe a flash update that needs to be done since there’s no clunking or anything? Has anyone else experienced anything like this? Just wondering if it’s an easy fix or if I need to take it in.

Thank you for your help in advance!

Nate
Belvidere, IL

 

[Joseph Garcia]

Do you have a bi-directional scanning tool to assist in troubleshooting?

 

[Doubeleive]

the engine shutting off really should not have anything to do with the transmission but I suppose it is possible.
I would start with the basics
check battery and cables, be sure the battery is good and that the alternator is charging. be sure the battery cables are clean and tight.
then check and verify fuel pressure.
then progress from there, but rule those 2 out first.

 

[Z71Burban]

Do you have a bi-directional scanning tool to assist in troubleshooting?

I don’t but a buddy of mine does. Maybe I should have him scan it before I take it in?

 

[Z71Burban]

the engine shutting off really should not have anything to do with the transmission but I suppose it is possible.
I would start with the basics
check battery and cables, be sure the battery is good and that the alternator is charging. be sure the battery cables are clean and tight.
then check and verify fuel pressure.
then progress from there, but rule those 2 out first.

Yea the engine shutoff was the wildest thing - that’s why I’m wondering if it’s possibly a CPU issue. After that I did check cables to make sure and those are all good and battery gage still stays WNL during long hauls so I’m assuming the alternator is good. How do I verify fuel pressure tho? I didn’t think of that

 

[Doubeleive]

Yea the engine shutoff was the wildest thing - that’s why I’m wondering if it’s possibly a CPU issue. After that I did check cables to make sure and those are all good and battery gage still stays WNL during long hauls so I’m assuming the alternator is good. How do I verify fuel pressure tho? I didn’t think of that

you can pick up a fuel pressure tester at most auto parts store's or harbor freight for around $25-30, autozone may also loan one for the same price you just leave the money as a deposit and get it back when you take the tool back.
then you want to connect it to the fuel rail and "if" possible stick it up under the front of the hood near the wiper area so you can see it while driving, usually they come with a extension hose for this purpose.

 

[Doubeleive]

the fuel pressure should stay fairly steady while driving, if you see it drop or it is all over the place and it's doing all the weird stuff and/or the engine shuts off then you know it's possibly a fuel pressure issue

 

[Joseph Garcia]

I don’t but a buddy of mine does. Maybe I should have him scan it before I take it in?

Yes, for sure.

 

[Z71Burban]

Yes, for sure.

Thanks man I’ll do that and post up on here with results. Appreciate it!

 

[Z71Burban]

the fuel pressure should stay fairly steady while driving, if you see it drop or it is all over the place and it's doing all the weird stuff and/or the engine shuts off then you know it's possibly a fuel pressure issue

Awesome! Thank you so much! I’ll give it a shot and see what happens!

 

[swathdiver]

If you have not changed the transmission fluid yet, do so soon. And either "flip the pill" or put in the new lower temperature transmission thermostat on the side of the transmission. It will extend its life as they typically die at 100K from the heat.

 

[Z71Burban]

If you have not changed the transmission fluid yet, do so soon. And either "flip the pill" or put in the new lower temperature transmission thermostat on the side of the transmission. It will extend its life as they typically die at 100K from the heat.

Thank you for this! Yea I think I should start there. Checked trans fluid - it seems to be over full and a little dirty but can still barely see a red tint.

 

[Z71Burban]

@Joseph Garcia @Doubeleive @swathdiver
I scanned it - here are the codes- now I’m freaking out

 

[Z71Burban]

@Joseph Garcia @Doubeleive @swathdiver
I scanned it - here are the codes- now I’m freaking out

And btw it just finally threw a check engine light on the way home from work today…

 

[Doubeleive]

@Joseph Garcia @Doubeleive @swathdiver
I scanned it - here are the codes- now I’m freaking out

well, I would go to a LEGIT transmission shop that has worked on these transmissions and see what they think, I am no expert but in some cases the techm can be replaced if that's all it is and there is no metal found in the pan. cases like that are rare but possible. you might be looking at a rebuild though.

 

[swathdiver]

@Joseph Garcia @Doubeleive @swathdiver
I scanned it - here are the codes- now I’m freaking out

Oh boy, I'm looking at the shop manual for my 6L80... well, here's what it says:

9 out of 10 transmission shops are going to want to either rebuild the entire transmission or replace it with a remanufactured one. A new GM reman and converter will run about $5-6K installed, maybe less depending on the market and dealer and comes with a 3 year 100K mile warranty and can be serviced nationwide.

If you want to know exactly what's wrong with it, get a bi-directional scan tool on it, like a Snap-On Solus or GMs MDI with GDS software on a laptop. Otherwise, you'll get the standard, "your transmission is bad, it's need to be replaced" answer.

As you can see, you might get away with a new valve body/TECHM and torque converter.

 

[Doubeleive]

Oh boy, I'm looking at the shop manual for my 6L80... well, here's what it says:

View attachment 392240View attachment 392241View attachment 392242View attachment 392243View attachment 392244

9 out of 10 transmission shops are going to want to either rebuild the entire transmission or replace it with a remanufactured one. A new GM reman and converter will run about $5-6K installed, maybe less depending on the market and dealer and comes with a 3 year 100K mile warranty and can be serviced nationwide.

If you want to know exactly what's wrong with it, get a bi-directional scan tool on it, like a Snap-On Solus or GMs MDI with GDS software on a laptop. Otherwise, you'll get the standard, "your transmission is bad, it's need to be replaced" answer.

As you can see, you might get away with a new valve body/TECHM and torque converter.

broken hub weld is a known problem, when mine was rebuilt they added extra welds to the new one to prevent that issue, basically the inside was welded all the way around where it breaks

 

[kentman]

A new GM reman and converter will run about $5-6K installed,

Been there, done that. I was $5.7K installed after $300 GM rebate back in August 2022 at 121K miles.

 

[Z71Burban]

Unreal - I should’ve kept my 03 z71…over 200k zero problems with motor or trans…was just literally rusting out.

It’s sitting now - only driving it when I absolutely have to incase it’s saveable. But had to go out yesterday and no check engine light (no I didn’t clear codes) and it’s shifting perfectly normal like nothing ever happened. So strange.

I have an appointment set on Tuesday to diagnose. I will update on here as we go! Thank you guys for all your help and support! I greatly appreciate all the advice!