HELP Transmission 2012 GMC Sierra 8 cyl 5.3L 4x4 146K miles

[swillson1980]

Hello everyone, new member here...truck prices are outrageous and I'm hoping I can salvage my 2012 sierra for a few more years...  Wrote a short story on what's led up to now...Hopefully there are some ideas for a fix that doesn't involve a new transmission (finger's crossed)...thanks in advance for any advice...

 

About 4 months ago my traction control/stabilitrak light came on.  I ignored it and it eventually went off thinking I could do without it for a while.  A couple months ago the truck started consistently jumping about 200 rpms every 5 seconds or so at 70 mph.  That evolved to doing it at 30 mph as well a week later.  I hooked up to my neighbor's computer and said change rear speed sensor.  I've done this before so I ordered part and installed on rear left wheel.  RPM jumping persisted at every gear, but mostly up to 3rd gear then it got less on higher gears, traction control problem fixed, but still no check engine symbol showing on the dash.  Sunday I cranked it up and heard a whine, almost like a pump trying to work around the transmission/oil pan area, then sound went away after a second or two.  Started driving and it would 'whine' every gear change for a short spurt.  Yesterday it started coming out of gear while driving, with a pretty good 'bucking action' associated with it...YIKES!  Yesterday afternoon, while idling at a light trying to make it home, it would not go into gear at all.  Turned it off, turned it on, put in drive and it would go for a bit then get out of gear.  Did this multiple times before figuring out I could go less than 20 mph and not allowing it to get above 2nd gear (I think).  The check engine symbol never came on through this whole ordeal (nearly 2 months) until yesterday when it wouldn't go in gear.  I'm kicking myself for not bringing it in to a shop sooner but I was trying to figure out a fix from internet experience and videos...to no avail...

 

So I checked codes with my neighbor's computer reader when I got home and got the following:

 

P0700 Transmission Control System

P0796 Pressure Control Solenoid C Performance/Stuck Off

P2723 Pressure Control Solenoid E Performance/Stuck Off

P2771 Four Wheel Drive (4WD) Low Switch Circuit

 

Trans dip stick doesn't indicate any fluid loss.  Any ideas?  I've read the 2014-2019 possibly had similar trans issues.  Bad TCM?  Solenoids?  Rebuild? New Trans?

 

I'd hoping some on hear may have some experience with this before I limp it over to a shop for any work.  Full disclosure, I'm not a mechanic by any means, just swap out some parts here and there such as rear wheel speed sensers, brake pads, power steering pump, oil pressure senser to date...I used to change my own oil but have had the dealer do it for this truck...truck does have a small oil leak but i'm guessing it's unrelated...

[Supreme Pizza]

Sounds like a major transmission problem. I doubt that any additives or fluid changes would help at all.

 

I have fixed some transmission problems by pulling the pan and replacing some electrical parts.

 

Some people that have had similar problems said that the torque converter was bad, and replacing it fixed the problem.
 

I do not know what is wrong with your transmission.

[Black02Silverado]

How many miles on the truck and has the transmission fluid been changed? 

[swathdiver]

8 hours ago, swillson1980 said:

Hello everyone, new member here...truck prices are outrageous and I'm hoping I can salvage my 2012 sierra for a few more years...  Wrote a short story on what's led up to now...Hopefully there are some ideas for a fix that doesn't involve a new transmission (finger's crossed)...thanks in advance for any advice...

 

P0700 Transmission Control System

P0796 Pressure Control Solenoid C Performance/Stuck Off

P2723 Pressure Control Solenoid E Performance/Stuck Off

P2771 Four Wheel Drive (4WD) Low Switch Circuit

 

 

It's time to rebuild your TECHM.  You can do this on your kitchen table for about $110 plus fluids without take the transmission out of the truck.

 

https://www.amazon.com/dp/B072C63HMY/?coliid=I1NOR87F2HVADM&colid=3MYY1OQK1UL4M&psc=1&ref_=lv_vv_lig_dp_it

 

 

Sonnax has a video on how to do this and there are other videos on youtube.  

 

This guy did it plus a few more things: 

 

The P2771 has to do with an ISS or OSS error of some kind.  Get a subscription to the shop manual at ALLDATADIY for access to the troubleshooting guide for all codes.

 

Keep the fluid clean.  Clean means its dead at 50k miles.  This is the first sign of trouble usually and it does not necessitate a full rebuild.

 

If you decide to replace the TECHM only, use only GM ACDelco and it will have to be programmed with a Tech-2 or equivalent.  A FAST LEARN ADAPTS will have to be run anyway, your friends scan tool might be able to do all of this, ask him.

[swillson1980]

Thanks everyone for the replies.  

 

I've had a feeling the torque convertor could be the problem as well.  I couldn't go any longer without a truck so I dropped it off at a local transmission shop and they are looking at it today.  Last week when I gave him the same description I put in here, he mentioned torque convertor.  He also mentioned $3200 for a rebuild, if that's what it takes.  Dealer where I bought the truck mentioned $4800 for a rebuild, and $5500 from a remanufactured transmission from the manufacturer but had a 3-4 month lead time to get here.

 

The truck has 146k miles and I have never changed the fluid.  Probably a big mistake?  I guess I've heard conflicting opinions on whether to change or not.  My last gmc (a 2002 model) went to 175k miles before it threw a rod and busted a hole in the oil pan at 10 years old; which afterwards I bought current truck. Never changed the trans fluid on that truck.

 

Is the TECHM a solenoid as in the P2823 code?

 

Thanks again for the info...

[Supreme Pizza]

All (most) transmission shops will tell you that you need a new transmission no matter what.

 

I needed a new transmission in a car once, and I took it to AAMCO transmission shop. The "mechanic" rode shotgun around the block, and said YEP - the transmission is shot and needs to be replaced. So I replaced the transmission myself with a brand new one. I took the car back to the same AAMCO transmission shop. The "mechanic" rode shotgun around the block, and said YEP - the transmission is shot and needs to be replaced.

 

AAMCO.

 

A.A.M.C.O

 

All

Automatics

Must

Come

Out

 

 

Anyway, here is a place that will replace the transmission with a rebuilt unit, and install it for free. For $2K. 

 

https://www.ebay.com/sch/i.html?_from=R40&_nkw=2012+gmc+sierra+transmission+rebuilt&_sacat=0&LH_TitleDesc=0&_sop=15

[swillson1980]

Funny you mention that about transmission shops because a story like that has motivated me through the years to research and try to do the work myself, if possible...

 

Wish they had that place down here in south Louisiana...I'd be in there tomorrow...

[Supreme Pizza]

Installing a transmission is not too bad. Need a lot of extensions for that one bellhousing bolt that holds the fuel line bracket on though.

[sb12]

My brother's truck is experiencing the exact same symptoms to the t.  What did you end up doing? I'm gonna try the tcm first

 

[alvocado]

My torque converter failed on my '11 Yukon 3 weeks ago and the symptoms were similar with RPM jumping, trouble finding and staying in gear and for the prior couple of mos., a noticeable hard clunk on downshift from 2nd to 1st when coming to a stop. Your stabilitrak error is a separate issue. 

 

If your TC is failing, you will need a rebuild. You have metal fragments throughout your entire system including the radiator and trans cooler/cooler lines that will need to be flushed with special equipment. It's not a simple diy and will require TCM coding if you swap in a different rebuilt unit. Find a reputable transmission shop to handle a rebuild and ensure they upgrade components to address known failure items. I paid $4300 for my rebuild.