Piston Slap: 6L80E…eeeeeek?

Sajeev Mehta
by Sajeev Mehta

Leather is better. (photo courtesy: image.automotive.com)

Nathaniel writes:

Sajeev,

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, and , 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?

Thanks,

Nathaniel

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 Corvetteforum.com 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 sajeev@thetruthaboutcars.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.

Sajeev Mehta
Sajeev Mehta

More by Sajeev Mehta

Comments
Join the conversation
2 of 55 comments
  • Hummer Hummer on Aug 04, 2015

    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)

  • John72830 John72830 on Aug 05, 2015

    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!

  • CoastieLenn For those that care to read the details of the crash NOT included in this article but published elsewhere- this happened at nearly 10pm when the CRV was stopped in the center lane of travel, lights off, with the driver remaining in the car. Not only is it not known if Blue Cruise was being used, it would have been a nightmare for most alert human drivers to mitigate that driving the 70+mph speed limit on many sections of I-10 in Texas, much less an AV system.
  • Jeff This is what I would want: Toyota has now released an affordable truck called the Toyota IMV 0. The newly developed vehicle made in Thailand comes with a rear-wheel drive and a gasoline 2.0-liter inline-four matched to a 5-speed manual transmission. NEW $10,000 Toyota Pickup Has Ford & GM Crapping ... YouTube · Tech Machine 8 minutes, 46 seconds Dec 26, 2023
  • Jalop1991 At the same time, let's take these drivers off the road--at least the ones that haven't yet taken themselves off the road.I can guarantee, at no point was this guy or any of the dead Tesla-stans actually driving the car. They were staring at their phones, because, HEY, SELF DRIVING!!
  • 3-On-The-Tree To Maintenance Costs His best friend did the union meetings and he said that there wasn’t a lot of negotiating taking place between the union and state because they were happy with how the state was treating them. He said it seemed more like a formality having the union.
  • 3-On-The-Tree He retired from the Navy after 25 years then worked for the Washington State Department of Natural Resources as a Wild land Firefighter for 20 years.
Next