By on August 4, 2015



Leather is better. (photo courtesy:

Nathaniel writes:


Long time listener, first-time caller. I’m responding to your plea for new Piston Slap questions. I purchased a gently-used 2008 GMC Yukon Denali AWD a couple of months ago. Other than its appetite for fuel, the only negative is that it has 141,000 miles. I believe the previous owner changed the transmission fluid at 100,000 miles (Carfax shows that the transfer case fluid was changed at this point, and I can’t imagine doing that and not doing the transmission). The fluid was relatively clean but I changed out several quarts via the dipstick tube using a fluid extractor after I purchased the vehicle, replacing them with the specified Dexron-VI. I believe the fluid level is correct but it’s difficult to read.

On a recent road trip, the 6-speed automatic (6L80E) transmission stumbled during the 2-3 shift while driving through the mountains and went into a failsafe mode. The check engine light came on. I pulled over, turned the ignition off and on again, and the truck operated normally. The CEL remained on for the next several ignition cycles. When I called OnStar to obtain the fault code, they could not retrieve it because the CEL was no longer on.

I was able to reproduce the problem by giving the truck wide open throttle. The 1-2 shift occurred normally. The 2-3 shift was delayed (the engine revved higher than the normal shift point of about 5,500 rpm), it eventually shifted into 3rd, and stayed there. The CEL lit up and the truck slowed down to about 40 mph, but it eventually allowed me to speed up, staying in 3rd the entire time. I pulled over, turned the ignition off and on again, and again it was back to normal. I called OnStar again, and they pulled codes P0700 (a generic code indicating a transmission problem) and P2714 (clutch pressure control solenoid stuck off). The CEL disappeared after a few ignition cycles.

A few TSBs, #PIP4304A and #PIP4184B, and 09-07-30-004A, appear to be on point. I’m not that familiar with how automatic transmissions work, but the TSBs appear to involve disassembly of the transmission and the possible replacement of valves, control modules, etc., which sounds fairly involved. I have not noticed a delay in the engagement of forward gears after putting it in drive, which I think is mentioned in one or more of the TSBs.

There appear to be no other mechanical problems with the truck. I see the options as follows:

  1. Do nothing for now, try to avoid full throttle upshifts, see whether the problem gets worse (how much danger is there in doing this?);
  2. Bring it to the selling (GM) dealer, beg for mercy on the cost of any repairs since they only sold me the car a couple of months ago (on the theory that any assistance they might provide is less and less likely as time goes by); or
  3. Take to an independent transmission shop. (Does anyone actually do repairs anymore or do they try to swap in a remanufactured transmission?)

Any advice?



Sajeev answers:

Fantastic assessment, especially the two hyperlinks. Kinda sad, however: the 6L80E is quite an impressive gearbox most of the time, like the robust GM 4-speeds before it. However, if your vehicle is (one of?) the first GM trucks using this gearbox, perhaps teething problems are par for the course.

Since you did the work for me, I’ll be brief:

  1. Not a bad idea, because this problem will likely take a long time to get bad enough to warrant removal/rebuild.
  2. A better idea: talk to your salesperson and ask for a referral to the service manager. Granted its a 6-7 year old vehicle with well over 100,000 miles, but there could be some goodwill in your purchase. Maybe a steep discount, hopefully a free diagnosis of PIP4184B (as per your thread) with their fancy pants Tech 2 diagnostic gizmo.
  3. Consider this after 1 and 2 run their course. Also consider something like a Jasper reman gearbox shipped to the mechanic of your choice; whatever works best in your part of the country.

I’d start with #2. If the dealership deems the fix within their tolerance for goodwill repairs, that’ll be great! If not, stick with #1 until the gearbox’s bad behavior is unbearable: save your repair/diagnosis for a bigger problem. Adding a new valve body to a gearbox that might have 140,000 hard, clutch-wearing miles of towing by the previous owner isn’t my idea of money well spent. You never know!

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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55 Comments on “Piston Slap: 6L80E…eeeeeek?...”

  • avatar
    Land Ark

    Not much to say here. I think Sajeev got it.

    GM cars might be non-competitive in a lot of ways, but one thing you don’t hear a lot are people with transmission problems. At least not to the degree you do with 90s and 00s Chryslers and Hondas.

    • 0 avatar

      Not trying to be snarky, but I’m not surprised that a truck transmission – which is designed to handle towing/hauling loads – would appear to be extremely reliable when many people only use it for commuting.

      • 0 avatar

        Well, to be fair, even on Ford and GM’s ordinary FWD cars, the transmission don’t tend to have problems…with a few exceptions, like the GM Lambdas.

      • 0 avatar

        You’d be surprised how driving behavior can damage a GM truck transmission. Take my grandfather’s truck, which we are talking about here lately since he has just passed away this past week (RIP).

        It’s an 02 Sierra extended cab, and it has 40k miles. It needs a new transmission because:

        -He drove with both feet, just like my grandma. So you’re straining a brake load on the trans all the time.

        -He liked to switch it into drive before he was done moving in reverse. You could hear this from the driveway as the transmission cried out in pain.

        Other than that, the thing is pristine and always garaged and washed religiously.

      • 0 avatar
        Carlson Fan

        You can’t say how many fluid changes that transmission has had either. It may still have the original factory fluid in it. My neighbor drove a GMT-800 ‘Burb to a 162K before the tranny finally gave up the ghost. He admitted that as the original owner he had never once changed the fluid or filter.

  • avatar

    I’ve dealt with quite a few GM and Toyota transmissions and the key is flushing! I’ve never dropped the pan on an AWD vehicle but I imagine that crud is your problem as indicated by the clutch sticking. If it’s the usual 30 or so bolts to pull the pan get a new gasket and filter and you should be fine after cleaning the magnets and other crud.

    • 0 avatar

      This. The transmission filter is not cleaned by fluid extraction and replacement; the filter itself needs to be removed, inspected, and replaced along with the old fluid. You wouldn’t change the engine oil and leave the old filter in place; the transmission is no different.

      If the transmission filter is plugged the oil starvation would have a huge effect the units ability to shift and cool itself and would explain why it went into limp mode.

      This might be a simple fix, but the longer it is put off the more expensive the damage will be.

      • 0 avatar

        I agree w/ Toad & LastDriver!

        It is possible that during extraction, vacuum applied to the case dislodged some debris, consequently, causing the respective valve to stick.

        Drop & drain the transmission pan.
        Measure the fluid drained.
        Clean the pan.
        Remove and replace filter.

        If you’re brave enough and can find a schematic you may be able to access the pressure control valve. If so, clean or replace it.

        Nurse it until the problem is resolved.

  • avatar
    87 Morgan

    To Sajev’s point, you most likely have one of the first units with the 6 speed transmission. I have always been under the impression that it came with the 09′ model year. I have never seen an 08′ with one. Regardless, I have seen plenty of GM transmission failures around the mileage band you have. Mostly on trade in units, owners find it cheaper to dump them than repair. If the store you purchased from is any good they ‘should’ at least pull the pan and clean it out for you.

  • avatar

    1. Bring the truck to the GM Dealer or a very reputable shop (transmission or otherwise) to replace the filter and verify the trans has enough fluid in it.
    2. At the same time, if that fails to remedy the problem, look at the TSB’s. Compare cost of doing TSB’s to driving trans until failure
    3. Drive it until failure. My bet would be that takes a while.

  • avatar

    If something has a filter in it, shouldn’t it be changed by 141K miles?? (By the way “gently used” and 141K miles don’t belong in the same paragraph, no less the same vehicle.)
    Great idea to have sales sent you to service.
    Try the cheapest fix first. Filter and fluid. I don’t get why mechanics seem reluctant to clean the pan/magnets and change the filter. I’ve always gotten the “it should be good for 100K” speech. I drive only about 8K per year and I don’t think fluid/filter changes every 6 or 7 years are overkill. Have your GM dealer look at it, pull the pan, clean it and Change That Filter!!!!!!

  • avatar

    If you were driving in the mountains, it’s possible that you were in the wrong gear for the incline/decline and something overheated…or simply that something overheated on a 140K-mile truck. Before you fret too much, I’d see if you can replicate the problem during ordinary driving on lower, flatter terrains.

  • avatar

    “…gently-used 2008 GMC Yukon Denali…141,000 miles.”

    We have different definitions of gently used. Over 20K miles a year is not gentle use. And that those miles, it’s well on it’s way to being used up!

    Gentle use is 7K miles a year, by an old lady, and garaged in her condo in Charlotte.

    • 0 avatar
      87 Morgan

      I see your point Corey, but keep in mind this is a GM product that was most likely sold in 2007. I have found the actual in service dates for them to be more on the July of previous year to June of current.

      Case in point my 08′ suburban was sold new September of 2007. My 08′ Wrangler in October of 07.

      You are correct that this a higher mileage unit that ordinary though. Best case scenario is 18k miles per year, whisk is more than average considering that mileage driven from 08′-11′ decreased substantially due to the economy.

  • avatar

    Regarding that shift lever…

    Am I the only one who wouldn’t want the stitching staring me in the face constantly? I know stitched dashes etc are all the rage but having it right there and at such a short distance like “LOOK STITCHING, OMFG” would annoy me.

  • avatar

    “2008 GMC Yukon Denali AWD”

    “the only negative is that it has 141,000 miles”

    “Carfax shows that the transfer case fluid was changed at this point, and I can’t imagine doing that and not doing the transmission”

    “I changed out several quarts via the dipstick tube using a fluid extractor after I purchased the vehicle, replacing them with the specified Dexron-VI. I believe the fluid level is correct but it’s difficult to read.”

    The fail is strong with this one.

    Ok kids, our first lesson is there are no “deals” on GMT900. Period. You have to buy this crap new, or be lucky enough to stumble onto one with no miles because you will pay out the rear end no matter what you do.

    Here is one identical to OP, 93K MY08 with the goofy AWD offered retail for 23,6.

    Here is an MY09 4×4 for 24,6, 80K

    Now let’s look at a subset of data.

    MY08 GMC Yukon Denali 6.2 V8 AWD

    07/30/15 FRDKBURG Regular $21,400 92,976 Avg BLACK 8G Yes
    07/16/15 PHOENIX Regular $19,700 97,917 Avg RED 8G A Yes
    07/15/15 DALLAS Regular $19,900 98,263 Avg BLACK 8G A Yes
    07/07/15 BALTWASH Lease $18,100 102,414 Avg BLACK 8G A Yes
    07/22/15 SF BAY Regular $20,100 103,617 Avg DK GREY 8G A Yes
    07/15/15 NJ Regular $19,500 107,067 Avg BLACK 8G A Yes
    07/08/15 CEN FLA Regular $19,700 108,656 Avg BLACK 8G A Yes
    07/30/15 DARLNTON Regular $20,100 113,592 Avg BLACK 8G A Yes
    08/03/15 NC Regular $19,100 113,961 Avg BLACK 8G A Yes

    and if we start getting into high miles and rough condition:

    07/29/15 CEN FLA Lease $11,200 152,474 Below BLACK 8G A Yes
    07/29/15 MILWAUKE Regular $12,500 182,235 Below BLACK 8G A Yes
    08/03/15 NC Regular $13,100 188,558 Below BLACK 8G A Yes
    07/30/15 DETROIT Regular $11,700 196,262 Below BLACK 8G A Yes
    07/28/15 ARENA IL Regular $12,000 210,846 Below WHITE 8G A No

    So its a consistent $20K clean/avg between 92-113K wholesale. I don’t know about you but I think 20K is kinda steep for a bailout era GM SUV north of 100K. Let’s step up five model years:

    MY13 GMC Yukon Denali 6.2 V8 AWD

    06/25/15 PHOENIX Regular $42,000 25,827 Avg SILVER 8G A Yes
    07/10/15 PA Regular $42,700 33,152 Above BLACK 8G P Yes
    07/29/15 SAN ANTO Regular $40,300 35,678 Avg BLACK 8G A Yes
    06/25/15 ATLANTA Lease $40,300 41,424 Avg BLACK 8G A Yes
    07/08/15 DFW Regular $39,996 43,209 Avg BLACK 8G A Yes

    So it doubles, great. But as past data has shown, *I can get 20K out of this with over double the miles in five years*. So… you float 40Kish, probably get a warranty, get 60K+ trouble free miles, and then trade in five years only losing $20K in depreciation. Otherwise you buy the truck at 20 and high miles, *are responsible for expensive repairs and any deferred maint*, and might be lucky to get 50% in five years. Rough models *today* are doing 60% of the cleaner ones.

    The next lesson is we don’t assume fluids were changed on a transfer case service. We also shouldn’t be removing important fluids though a $9.99 Autozone tube ourselves, we should be taking our vehicle to the transmission shop for fluid exchanges. Oh and every transmission specialist I have ever met will tell you to drop the pan and exchange its fluid, never to attempt to drain the torque converter (I’m not saying Op did this I’m just adding this point).

    Sajeev has the right idea in seeking help from the dealer. I would also avoid goofy applications of “AWD” in the future and stick to 4×4 in my truck choices or I would have bought a newer Ford Expedition:

    MY13 Ford Expedition XLT

    07/23/15 DFW Lease $31,000 23,134 Avg WHITE 8G A Yes
    07/29/15 SAN ANTO Regular $32,000 24,691 Avg BROWN 8G A Yes
    07/29/15 NJ Lease $33,500 24,979 Avg DKBROWN 8G A Yes
    07/15/15 DENVER Lease $35,100 25,995 Above WHITE 8ET A Yes
    07/22/15 TAMPA Factory $30,500 45,217 Avg WHITE-UG 8ET A Yes
    07/20/15 SAN ANTO Lease $23,901 50,657 Below SILVER 8G A Yes
    07/21/15 ORLANDO Lease $26,400 52,011 Below WHITE 8G A Yes

    07/23/15 DFW Lease $31,000 23,134 Avg WHITE 8G A Yes
    07/29/15 SAN ANTO Regular $32,000 24,691 Avg BROWN 8G A Yes
    07/29/15 NJ Lease $33,500 24,979 Avg DKBROWN 8G A Yes
    07/15/15 DENVER Lease $35,100 25,995 Above WHITE 8ET A Yes
    07/22/15 TAMPA Factory $30,500 45,217 Avg WHITE-UG 8ET A Yes
    07/20/15 SAN ANTO Lease $23,901 50,657 Below SILVER 8G A Yes
    07/21/15 ORLANDO Lease $26,400 52,011 Below WHITE 8G A Yes

    • 0 avatar

      Point well taken, but as a former owner of a 540i, I’m a masochist when it comes to vehicles that need a little attention. At least the GMC doesn’t leak random fluids all over my driveway.

  • avatar

    So are they pulling a Bravada with the Denali, and doing a one-model AWD system? If that’s the case I’d be real scurred, and get something else.

    Other note: My cousin who lives in TX, while in town for my grandfather’s death is shopping Expeditions, because they cost (according to him) 3-4K more out there than they do here.

  • avatar
    Carlson Fan

    If you don’t know when the fluid/filter was done last, I’d do that and drive it. That transmission should make 200K easy if it’s treated and maintained correctly.

    Also check the air ride suspension on your Denali. If it’s original it’s likely toast. Our ’07 ‘Hoe needs a new compressor, rear air shocks and front shocks with the electronic dampening. At least of $1000 in parts if I do the work myself. And that’s getting by cheap.

    • 0 avatar

      How do you check the air ride suspension? I’m not getting any “service autoride” errors, and it rides great on the highway (a little truck-like around town, which I expect since it’s a truck).

      • 0 avatar
        Carlson Fan

        I haven’t gotten any errors either and it actually doesn’t drive that bad. But I’m sure once I get everything fixed I’ll realize how bad it actually is. Someone may have serviced yours already at some point. There are conversions to completely eliminate it all together.

        My first sign that it wasn’t working was when I hooked up my boat (which has about 400 lbs. of tongue weight) the compressor wasn’t kicking on to level the truck like it did when it was new. Also it sounds like the front left wheel is ready to fall off and I’m sure it’s because the strut is shot. Ours has 110K on it so they are way over-due. For a BOF tank SUV it has an awesome ride when the system is working like it should which is why I will spend the money to fix it.

        And be glad you have the 6.2 without the AFM. At least you have no worries about oil consumption with that motor like I do with the 5.3/AFM.

  • avatar

    The OP mentioned they changed the transmission fluid when they got the vehicle, how long between the change did the problems come to light? I wonder if maybe the wrong amount of fluid was put back in?

    But a GM transmission in a Denali going out at 141k miles wouldn’t surprise me at all, especially considering the previous owner may have used it to tow.

    I know I had a family member with basically the same vehicle that was an Escalade and you could feel the thing slipping after about 110k miles. And he was very fastidious with maintenance. He had an incredible amount of issues with that car, even the Cadillac dealer couldn’t figure out a major one so he dumped it. He swore off GM over it, and he was a loyal customer for decades.

  • avatar
    Firestorm 500

    At 141K miles, that dealer doesn’t owe you a thing. Neither does that transmission.

    If you wanted a warranty on major mechanical parts, you should have spent more and got a newer vehicle with less miles. Maybe a CPO unit.

    As far as changing the transfer case fluid, I have changed it several times on my Jeeps and not changed the transmission fluid at the same time. They are two separate components. They use a different maintenance schedule.

    • 0 avatar

      “At 141K miles, that dealer doesn’t owe you a thing. Neither does that transmission.”

      Depends on how much profit they made on the deal and how much they embrace the Goodwill concept.

      • 0 avatar
        Firestorm 500

        I’ll bet he signed an “AS IS” document. Maybe more than one. In the F & I office. The F & I guy would have explained it to him.

        I do sympathize with him, but I believe going to the dealer and crying for help is not reasonable given the age and miles of the vehicle.

        Profit and Goodwill are are all well and good, but rebuilding a transmission on an AWD vehicle can be $2,500.00 and up real quick.

        • 0 avatar

          The transmission, not the transfer case sounds like the problem, so regardless of being AWD or 2wd the cost shouldn’t be different out side the labor in dealing with two components upon removal. Which I doubt would cost $.01 more.

    • 0 avatar

      @Firestorm 500. and @Sajeev as well.

      Heh. We bought a GMC Acadia CPO with 40K on it, and it was immaculate. It literally looked new…before it was detailed. The week after we passed 100K, the engine threw a rod. GM’s response? “Oh it’s out of warranty and you purchased it CPO…we can’t do anything about it”

      $7000 fix.

  • avatar

    Problems with the 2-3 shift solenoid is well documented from 2008 to mid-2009 when addressed.

    Typically rears its ugly head early, in warranty period.

    You just weren’t lucky. It isn’t a break the bank fix, but it isn’t cheap. $1,200ish IIRC YMMV

  • avatar

    Take it to a good transmission shop. Have them service it and replicate the problem for them if you can. Take advantage of their knowledge. Postponing a repair might cause a simple problem to snowball into a total rebuild. My buddy took his one-ton Dodge with 200,000+ miles to They replaced a couple of parts and got it shifting like new again.

  • avatar

    I personally would NOT use AAMCO, they use junkyard parts, and I have confirmed this in one scenario and would have in two if I had been willing to look before I sold it. (Wasn’t working correctly when “fixed” only happened when cold)

  • avatar

    Hi folks, long-time lurker (at least a year, probably two), but finally a brand new member. Not that this, my first post here, is related directly to 6L80E issues, but I also picked up a “gently used”, 140,000 2008 Denali several months ago. Transmission may have flared on the 2-3 upshift once or twice, or I may have just been looking for problems, but, nevertheless, I’ll be changing fluid and filter this weekend. It can’t hurt, and normally since I usually buy at 100,000+, fluid changes are something I do as preventative anyway. This article just motivated me to do this sooner than later.

    Anyway, the point I’d like to share is this: These things, in my opinion anyway, are a blast to drive. Yes, I suppose I’ve led a sheltered life, to think that a full-size BOF SUV can actually accelerate, corner, handle, and stop better than my “performance” cars. I have a 1988 Corvette and a 1996 LT1 Trans Am, but the Denali outperforms them both, in actual driving fun. I suppose the difference is in a decade or two of technology, but still…

    Anyway, B&B, don’t shred me too badly, but I just felt like sharing!

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