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Discussion Starter · #1 ·
I just joined the forum last night. I'm desperate for some guidance on the random shifting issues I am having with my 2011 GMC 3500 Sierra 4wd. It started a couple weeks ago. I pulled up to a job site and when I went to leave and put it in gear, I got the "shift inhibited" message and it would not go into gear. It may happen several times A day now or it may go for several days with no problems. Sometimes I start the engine and after idling normally for a few seconds, it suddenly goes into a high idle and it may not go into gear at all or it may go into gear with no error messages but shift extremely erratically. Last night I ended up driving home from the job site in 4th gear because I had only reverse and 4th. Luckily I didn't hit many red lights! This morning I went out and started it and it shifts flawlessly! The only constant in all this is that once I start the truck and put it in gear, whatever state the tranny comes online with, it stays that way until I turn off the key and restart it. It never goes from being erratic to shifting normally or vice versa without shutting off the Ignition and restarting it. I'm 99% certain this is an electrical issue, but where do I start to track it down? Should I start by changing out the Ignition switch? Or should I just start combing through all the wiring until I find a broken or bare wire? It is throwing no codes, except a mechanic friend of mine put his reader on it in there was some code about the brake system and I didn't write it down, but I don't know if that is related at all. Also my cruise control quit working just a couple weeks before these issues all started taking place. I'm running an H&S Mini Maxx with medium boost and DPF delete. Otherwise everything is stock. Any help in focusing in on potential problem areas would be greatly appreciated!
 

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2015.5 Silverado LTZ 3500 SRW
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If there is no check engine light and no codes, I would question the tune. With the issues you described, there should be codes.
 

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The 11’s are notorious for the tcm to go out.
 

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Discussion Starter · #4 ·
If there is no check engine light and no codes, I would question the tune. With the issues you described, there should be codes.
No check engine light. But I did just pull up codes again and this one keeps showing up:
P0571 brake switch A circuit.
Any ideas?
 

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Discussion Starter · #7 ·
After further research, looks like the P0571 indicates a problem with the brake switch. Any idea which one is indicated by "circuit A"? That would also explain why my cruise control quit working.
 

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2015.5 Silverado LTZ 3500 SRW
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Replace the brake switch. It's a common problem.
I don't know if that will fix all the issues you have.
My guess is your transmission internal mode switch is failing.. Without codes, it’s just a guess.
 

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Discussion Starter · #10 ·
Replace the brake switch. It's a common problem.
I don't know if that will fix all the issues you have.
My guess is your transmission internal mode switch is failing.. Without codes, it’s just a guess.
I didn't have time to change the brake switch right away so I spent a few days just pulling over and clearing the P0571 code whenever the tranny started shifting badly. It would shift normally after clearing that code. I did go ahead and pick up a brake light switch to have in case things got really bad. Well, yesterday it got to where the truck was almost undriveable because of erratic shifting, so I dove under the dash and changed out the switch. Couldn't believe it! My truck went from acting like a bratty little kid to shifting like a champ! All tranny shifting issues fixed with just a brake light switch! And the cruise control works again! $22 well spent!
 
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