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Need help diagnosing my 6l80 trans. Truck has 120000 miles, trans fluid and filter were just changed about 1 month ago. I was driving the other day when my truck made some grinding noises coming off a stop sign and fell out of gear and would only rev. Managed to coast to a parking lot and cycled the key. Shifted into Drive and trans started making whining noise but went into gear however fell out as soon as I gave it some throttle, same in reverse and manual gears. Was able to load the truck up on a trailer by constantly starting and turning off engine and moving forward a few inches before falling out of gear. Got home and checked for codes, found codes (U0073 Can Bus A Off) (P2723 Clutch Pressure Solenoid E/5 stuck off) (C0800 Power Module issue) and (P0700 Generic trans problem code). Checked trans oil and it was dirty and burned with small metal flakes in it so I figured it was some internal issue like pump and clutches. Dropped the trans, opened it up and found a ton of metal dust and a few flakes in the pan. Tore into the clutch packs but none of the clutches were burned up or over worn, all be it a bit worn but not worn out. Pump had some wear on the bell housing but nothing emery cloth couldn't smooth out. Valve body seems normal and all the check balls are fine. No noticeable issues with seals or gears or valves. Did a resistance test on the Can Bus and it passed with 61ohms and the correct voltage readings. Im figuring the TCM/Solenoid Body because the Can Bus code, Solenoid E Off code and Power Code Along with Torque Converter because all the material in the pan and whining noise. Figured Id go ahead and replace the clutch plates and pump seals as well while I'm in there. Am I on the right track or could I be over looking something? Are the new TCM units from the dealer plug and play or would it need to be flashed first? Can these issues be explained by these components? Thanks

I've read a bunch of different posts on transmission issues and the like, but I'm simply looking to do a fluid and filter change. My truck is a 2015, 5.3, 6 speed - I'm assuming it's the 6L80, is that right? I know it takes Dex VI, just not sure how much. 75k, and it's not been changed yet. Plan on doing both diffs, transfer case, and transmission. I've got Mobil 1 75/90 for both diffs. I know I need 2 qts of Dex VI for the transfer case, just not sure how much for a fluid/filter change for the transmission. I'm assuming synthetic is preferred for the transmission and transfer case?

Possible cause of DTC P0777 for a 6L80 transmission - especially after a re-build, upgrade, or maintenance of the valve body (a chapter from my upcoming book, "Learn from my mistakes!") Here's the context: 2007 GMC Yukon Denali 6L80 Transmission (Early, 1st Design, original equipment, no prior work or refurbishment actions taken on this transmission/valve body/TEHCM (TCM) - just trans fluid change and filter change) 195,000 miles (not bad, eh?) 6.2 Liter L92 engine (Original Equipment, no serious work has ever been needed, never rebuilt - just well maintained) Vehicle is - from an interior perspective - 95% 'new'. I've spent the last couple of years restoring it. I've spent time and money on everything from new carpets to a new dashboard, HVAC assembly (in-dash), new seats, new seat motors, new windshield, new everything, for the most part I've done all this work myself. I've built up quite a tool collection and quite a bit of knowledge I work in the world of IT (Digital Experience Strategy for large and medium-sized companies) Being in this field of IT means I work all day in a world of total ambiguity and chaos where nothing is ever cut and dry and the options, ideas, and risks are endless...as are the personalities I deal with. Working on my vehicle - along with vehicle's owned by friends and family aware of my growing skill-set - provides me a level of calm and relaxation I can't find elsewhere How This Story Originates: In the last 4 to 6 months, I've noticed the transmission exhibiting a moderate 'clunk' when - IMO - it is shifting down from 3rd gear to 2nd gear, or during any low-load, low-RPM upshift from 2nd to 3rd gear. This happens only when there is low RPM / low 'Load' on the engine...followed by a quick increase in requested 'load'. For context, a situation wherein it commonly happens is during a slow-down at a stop light and my intentions are to turn right. I.e., 'right on red' with a slow, cautious crawl for safety. Assume no cars / traffic to negotiate (for simplicity). I'd say I'd be going at about 10 to 15 miles per hour...perhaps as much as 20 to 25 miles per hour...from a pre-braking speed of ~30 to 40 mph. I would take my foot off the accelerator about 100 to 150 feet before the red light and apply light braking. Once I'm in a position to begin my right turn safely, I would take my foot from the brake and apply ~30% to 50% throttle on the accelerator. At this point wherein I engage the throttle, it seems as if the transmission doesn't know which gear to be in. While it only takes about a second, it eventually chooses 2nd gear but in the process it makes a noticeable 'clunk'. To mitigate this 'clunk' I usually try to feather the throttle up a little bit before I'm about to release the brake (i.e., 2 - footed driving). Slowly getting the RPM's up above 1,000 before starting my right turn and releasing the brake seems to negate the clunk. I've also noticed this clunk never really occurs until the transmission fluid temperature reaches about 110 (or above) Fahrenheit ( + /- 10 degrees). All other gear shifts in all other situations are rather comfortable and exhibit no observable issues. The transmission (nor the engine) never produces any DTC codes. Using a capable scan tool to reset the Trans Adapts and manually doing the Garage Shift procedure doesn't result in a 'fix'. Neither has anything else I've tried. I have not - to this day - ever tried doing a "Service Fast Learn". This is a procedure only incorporated into a few of the highly expensive scan tools such as the OE Tech2 and the Snap-On. My Autel Maxisys Elite definitely doesn't have this special function. One of these day's I'll have this procedure done by the Dealer or someone with a capable tool. Last weekend, I decided to install a Sonnax Zip Kit for the 6L80. My thought process was that the temperature increase of the trans fluid was a key indicator and gave me good direction. I was thinking pressure was being lost when the internal components of the valve body heated up to a certain point and expanded ever-so-slightly...we're talking a thousandth or so of a millimeter in various places throughout the valve body veins / assembly...but enough where some trans fluid pressure was being lost in key areas and causing the resulting clunk. Because the valves themselves were a different metal (and some of them a type of polymer / plastic) and probably not expanding like the valve body casing, I figured this was a good enough hypothesis to start working against. The Troubles Begin.... To make a long story shorter for you TLDR-er's, the Zip Kit is now installed and the shifting concerns seem alleviated. I'll give it another couple weeks to make a full conclusion, however. But the big story I wanted to share was about a mistake I made during the installation of the Zip Kit...but I imagine it could happen during any valve body refurbishment, upgrade, or maintenance. It has nothing to do with the Zip Kit itself. The Zip Kit was well manufactured and has fantastic instructions...with pictures too! The Zip Kit installation - plus a desire to inspect and clean all valves - simply gave me the opportunity to make the massive screw-up which occurred. So to help out fellow techs or DIY'ers who may experience this in the future, I have attached a summary pictorial explaining what I did and what it caused...along with the now-obvious solution. Initial Start-up and Test Post-Cleaning, Assembly, Refurbishment - aka, "The Crucible": What should have taken just about 3 hours to complete ended up taking 4 days. After putting everything back together the first time, I started the vehicle. I left it in Park for about five minutes. No unusual noises, no "Check Engine" lights. Normal oil pressure, normal slow rise in trans fluid temperature. Normal idle RPM's. I shifted from Park to Reverse and back to Park - allowing about 3 seconds between each move. This was an effort to flush air out of the veins/pump which may have accumulated during the overnight hours (I started this job in the evening but didn't re-install the valve body and other components until the next morning.) I then shifted from Park to Drive. I expected - as one usually does - to feel the torque and the car's desire to move forward. But no, there was no forward engagement whatsoever. I then shifted back to Park and let it sit for a minute. I shifted to Reverse - no reverse engagement. I left it in Reverse for 5 to 10 seconds thinking it will engage once the 'air is pushed out from the pump and valve body veins'...and that's when the Check Engine light came on. Silly me. I put it back in Park. I figured, let's try this again...maybe it was a solar flare or perhaps CNN is talking about Mueller again... Nope - same bad result - no forward, no reverse, not even the sound of it trying to engage. From Drive I was moving the shift lever back towards Park...and during that time I stopped briefly at Neutral. A faint squeal noise was observed from the transmission. Knowing that a squeal noise coming from a transmission is not SKOOKUM (h/t Ave on YouTube - one of my all-time favorites), I left it in Park and shut the engine off. Exhausted, bewildered, and full of self-doubt, I removed the valve body and TEHCM two more times. For anyone familiar with accessing the transmission valve body on a 2007 - 2013 Yukon (and perhaps 2014 and beyond), you know it's not easy. Each time, the catalytic converters need to be moved / dropped. This means the O2 sensors need to be removed, the front drive shaft needs to be undone and moved off to the side a bit, the front right wheel and wheel well cover need to be removed, etc. etc. ....in addition to draining the trans fluid oil and making a mess of your garage floor and yourself. I did this without a lift...only a jack and jack stands...making me ache and strain in ways I haven't felt in years. Note to DIY's...it takes the catalytic converters a bit more time than you think in order to cool down to a manageable level...ask me how I know. Each time I went over the instructions for the Zip Kit step-by-step to make sure I put the pieces where they were supposed to go. Each time I questioned most everything about how I put things back together - were the seals matching up correctly? Were the electronics / wires completely connected? Were there any green fuzzies on the main connector going from the outside of the trans and into the transmission case? Were there any cut or broken wires I didn't notice or failed to inspect? Each time I examined every piece that I had touched and questioned everything!...or so I thought. The struggle was REAL! Approximately 8 liters of new Dexron VI ATF - along with both hands, the right side of my jaw, and my lower back - were abused in the process of this event. The Cause: In short, during the re-assembly of valves which I had removed for cleaning, I put two of them in backwards. When they were first re-installed, they seemed to fit and it appeared how I re-installed them was exactly how I took them out. But I was incredibly wrong on both points. It wasn't until I noticed the ATSG manual's depiction of the valve body assembly diagrams - and comparing them to how I had re-installed my valves - that I finally realized the reasons for DTC's p0777 and p0700 suddenly appearing. For SEO, (but explained in the pictorial), I'll simply say that DTC p0777 is "Clutch Pressure Control (CPC) Solenoid 2, Stuck ON" and was the only result post-assembly and start-up. However in the end there was nothing wrong with solenoid 2 whatsoever. The TCM/ECU only threw that code because the situation matched the DTC p0777 trigger conditions. At that point I was really close to spending ~ $600 bucks on a new TEHCM...and that's when I noticed I had installed Clutch Select Valve 2 and Clutch Select Valve 3 backwards. THANK THE GOOD PEOPLE AT ATSG WHO MAKE GOOD TRANSMISSION MANUALS..SPECIFICALLY THE DIAGRAMS (if only they were in color, btw.) Now getting people to read carefully...a different story , of course. I couldn't find too much on DTC P0777, so I suppose it's rare. But if you ever come across this DTC or other "solenoid stuck", "solenoid failed" types of codes - and especially if you've just completed a refurbishing / cleaning / Zip-Kit installation on your valve body - take triple notice of how you reassembled and re-installed those valves....ALL OF THEM! Thanks for your time, Jeff Alpharetta, GA

Well, seeing as how I can't find much on this subject no matter what forum I go to, why not try to start the discussion here and see what kind of following I can get and see where we end up. If you're reading this thread, chances are you have thought about modifying or swapping out your current transmission in your 2014+ GM truck. In my case, I don't mind my 6L80 in my truck. It does fine for what I do right now and it's holding up just fine, but I think the big issue is when you start to search for big power (like I'm starting to do), that 6L80 is not going to hold very much (or so we think). Now, let's all face it. We've seen posts after posts, comments after comments, photos, videos, etc. of guys with built motors with turbos or prochargers shooting down the quarter mile in search for the best time on these 6L80s. Some say they're completely stock, others have them built, and we all ask ourselves the same question: Reliability. How well are these transmissions going to hold up to the abuse on the track? Especially if you want to make it a fast street/strip truck and drive it back home to the garage afterwords. We know for a fact that 6L90s can hold quite a bit of power. Even though I've mostly seen it in Camaro ZL1 applications, there is a guy on YouTube (GuitarmaggedonZL1) who is running a stock 6L90 on stock converter making 1000HP (give or take on an unloaded dyno) and the transmission hasn't puked all over the ground just yet. (Exaggeration, I know.) So, needless to say, a 6L90 swap sounds nice, at first... After you figure the extra length and weight (and in my case, relocation of the transfer case and getting custom driveshafts made), it starts to look a bit unpromising, but still not out of the ball park yet since it will be able to handle the power some are seeking, but where these newer transmissions lack significantly if you want to do boosted applications at the track (or even just launch control on N/A), no one has developed a transbrake. Very, very few forums are talking about this, and only one video exists of a guy in his BMW testing out a transbrake on a 6L80/6L90, and who knows how reliable it is. So, now, you start to think: Well, gee. What can I do now? How about a TH400 or 4L80e swap? So far, I've seen few posts on that as well. No one is talking about it, and I think the biggest problem people seem to be facing is the new PCM: E92. Also possibly the fact that the TCM on the newer transmissions is inside the transmission and whatnot, but whether that plays a part in this, I don't know yet. Now, adapting a TH400 or 4L80e can be done (most likely with a different bellhousing since the bolt holes are in a slightly different spot), but you run into the issue of getting it to speak/cooperate/communicate with the new E92, which I don't think anyone has tried. The only video I've seen of anything working in this application was on a 1320Videos video with a Nova where they were using an LT4 long block (built motor to 388 C.I.) and twin turbos, and it had a powerglide in it. Don't know if it was a manual valve body or computer-controlled, but what I do know is that they used the factory computer to run the DI injection system and piggybacked the rest to an MS3 Pro. After dealing with some issues, they were able to make that thing boogy to a 9 second pass at 148mph. So, these engines have potential to haul ass, but we just haven't figured out how to crack the system. So, at this point, I'll just leave what I've discussed here and see where the thread goes from here, and I'm hoping people chime in and vendors are watching/listening. Even though the demand isn't hot for it right now, there's going to be a surge for good transmissions when people can buy these trucks/cars/motors/transmissions for pennies on the dollar. Unfortunately, I feel like we'll have to wait that long in order to see results, but oh well. Just to give you guys an example: In the next year or two (2019 or 2020), I'd like to go turbo with my truck. (Doing all the supporting mods before going there minus built bottom end until I see where I can get with stock bottom end before sending a rod through the block or oil pan) Ideally, it'd be best to have a transbrake in that application with 2-step, but can't do it on the new transmissions. So, 4L80 seems to be the option, but I can't do that either because no one supports adapters or harnesses to make them work with the new motors/ECUs. That's the boat I'm in. I like to research everything before I go whole hog into something. Risk assessment, I guess.

Bought this for one of my father in law's project cars but it looks like he may have found a different motor for it. Was said to have 8k miles on it, and looks almost new. Asking $4000 for the motor, trans, rear end, and computer/harness/pedal.

Howdy, I own a 2010 Silverado that is doing some weird stuff. First off, let me tell you the mods that are done: Yank 2800 Stall, TSP long tubes, Borla Cat-Back system, K&N cold air intake, some random after market spark plug wires that came off a 2011 Camaro SS, and it has a custom tune done with HP tuners. This is a 5.3 LC9 with a 6l80 transmission (with stock clutches besides the stall). Now let me tell you the issue. If I am cruising at low speeds and mash into the gas it will sometimes wig out. It shoots the rpm's to 6k and unlocks and locks the doors (almost like it's trying to throw it in park). This doesn't happen all the time, only at low speeds and if I haven't touched the gas in awhile. I'm almost ready to pull the converter off and throw the stock one back on, but part of me thinks it might be an electrical issue. I had the transmission pulled out and the stall rebuilt back in December and my transmission guy said it's one of cleanest 6l80's he has ever seen, so I'm hoping its not my clutches. Let me know if y'all know anything about this type of problem, but everyone I've talked to so far has no clue. This sucks because I was planning on doing a TSP cam and DOD delete this summer, but that will have to wait! -David

So I was heading home from work and decided to fuel up with 91 octane and used the fuel system cleaner at the pump. Approximately 20 miles out of town my truck started to surge and the RPM's jumped on every surge. I thought it was the fuel until. The next day I stopped at a stop sign and when I eased my foot on the pedal the transmission acted like it was not engaged in 1st gear and then slammed into gear. I found a transmission at a wrecking yard but I'm not sure what caused this and am afraid the problem may still exist with a new tranny. Has anyone ever experienced anything close to this?

New to GM-T, but not forums in general. I have a list that I follow for reasons explained below. I found this site and figure it would be a good site to contribute to for a couple of reasons. My DD is a 2006 GMC Sierra SLE extended cab, bone, bloody stock with 186K miles. Well, other than a Rough Country 3" leveling kit and new sound system. 1. I do not like the way that the GMs tend to droop in front, and the OEM sound was, like totally shot. Other than those two items, no issues with it so far, but it is pushing the mileage where stuff, major stuff, could start going wrong. I do my own wrenching as much as possible so having a site dedicated to the truck is a good thing to have. The second, and probably the primary, reason is that when I am done with my '88 Blazer rebuild . . . oddly enough with just about the same number of miles, 195K, I believe . . . it will be more late model than production year. By late model I mean the 14blt FF rear diff is out of a 2009 2500 HD Silverado, the motor & tranny are 2008 LY6/MYC (I think I got those correct. It has been awhile since I had to remember that), custom NP241 TC, 2008 DIC and instrument panel & electronics (If I don't update to something newr before I get to part of the build), '88 D60 front diff 2006 Tahoe front & 3rd seats, etc. All of '88's electrical and electronics are either going to be from the '08 or totally updated to improve the power quality to the electrical devises, i.e. window, door locks, etc,. So, while the body and frame are pretty much vintage '88, the drive line from the cooling fans back to the rear diff as well as much of the cabin interior are going to be late model. 2nd tier is an ECS out of a Sclade or crew cab, but I am not sold on that much work or expense yet. If I find a system that falls in my lap, I amy figure out how to get it in . . . changing from a vacuum to an EMA system may be more intriguing than desirable. So, between the '06 GMC and the late model drivetrain and electronics on the '88, while a lot of the posted stuff I have read so far is late model glitz and glam; stuff that sounds good in a conversation or looks good on paper, but doesn't do much for driving it to the office, grocery store, or the golf course all that much, the tech talk seems to be pretty straight with the performance upgrades and the maintenance discussions. For the '06 I am interested in posts on vehicle specifications, general operation, reliability issues, maintance discussions, worth while performance upgrades and good tech stuff like that. As for the '88, I am going to put just a mild cam in the LY6 to boost HP a little bit, and I am hopeing someone . . . which I have found aleady seems to be the case . . . knows their way around HP Tuner because between here and LS1 I am most like going to be looking for some serious assistance when it comes to getting the motor and ECM package to function correctly in that old truck. I think it is getting late here. I will be posting some of the social stuff allong with pics and stuff in the next few days. Looking forward to the good reads on this site and glad I stumbled across it. I found it by the way while looking for specifications on the OEM torque converter installed on the '08 donor. Didn't find the specs here yet, but found a good read on the operation of the 6L80/90e tranny. Duke

My truck has 123K miles on it. The transmission is a 6 speed 6L80. About a month ago I was towing a 23' 8'6" beam, 5000 pound ski boat about 300 miles. The transmission temp maxed out around 193. About 100 miles before our destination the check engine light came on. It was late and we were going through small towns so I did not have a chance to check the code. I was in tow haul mode and never noticed any issue. The next day the CEL was gone. Yesterday I was driving around unloaded and had the truck fail to shift and rev up to 3K+ rpm. At that time I noticed that the CEL was back. I was half a mile from home. I do not believe that it shifted on the way home, it seemed to be locked in gear. Once home I stopped and restarted the engine. After restarting the CEL remained but the transmission seemed to function normally. Later I drove 15 miles into town to have the code read. The codes were P2715 and P0700. I did not ask to have the codes cleared. I have had an issue with the 1st to 2nd or 2nd to 3rd shift where it seems to be a delayed shift with some revving between for years. This seems to happen when I am not accelerating hard or loaded. Today I drove about a 25 mile loop to talk to a transmission guy I know and take the kids for a snack. On the way I shifted manually up and down through the gears. It shifted smoothly. On a short divided highway section I floored it to accelerate. It downshifted twice. The first was smooth and good. It seemed to have some free revving with the second, although I may just be overly critical about this. The transmission fluid was changed approximately 10K to 15K miles ago. I am hoping that others can share their experience with and solutions for similar issues with this transmission. What do you guys suggest? Thanks in advance.