Hello all. I have lurked this forum for a while. Great place and part of the reason I switched to Duramax.

I just purchased an 06 LBZ and after only 1200 miles I have experienced my first problem. Today I pulled my boat for only the second time (8,000lbs), and on the way back from the ramp, which is only 5 miles from the house, my RPMs started to creep up and my MPH started to fall. I went from 40mph to about 15mph and that was all it could manage.

I made it to a Food Lion parking lot, but made the mistake of slowing to a complete stop for a speed bump. I was unable to generate enough momentum to get over the speed bump. RPMs would rev, but it would only crawl an inch at a time. I tried manually shifting, even 4WD, but no luck. I was stuck, with a pile of people irritated at me.

After a friend came to the rescue, I unhitched and was able to pull away from the trailer so he could take the boat home with his truck. I was able to get up to about 40 mph without the trailer, but with noticeable loss of power, especially when I had to go up a mild slope.

Gears shifted smoothly, but the whole process seemed really weak. I wish I had the vocabulary to explain this better, but I don't. I don't think I would have been able to get up a steep incline.

I feel lucky that this all happened very close to home. Does anyone have a guess what might be the problem? I'm taking it to the dealer in the morning, but would appreciate any advice from the experts out there.

Many thanks,

Joe

BTW. Truck is stock, no mods. No visible error codes on screen.

Tranny slip? Limp mode?

i dont know what to say.
bad load of diesel?
cloged filter.
it sounds like the trans is really slipping.

i dont know what to say.
bad load of diesel?
cloged filter.
it sounds like the trans is really slipping.Sounds to me like a plugged fuel filter from a bad tank of fuel.

When and where did you fill up last?

I've had clogged fuel filters before in my previous trucks, and this doesn't feel the same at all. There is no choke, hesitation or sputtering sensation when I press the accelerator. It revs up very smoothly. 3500RPM was as high as I dared, but it could have easily gone higher.

It pulled fine going there, but coming back about 1 mile from the ramp, it just started to slip. Eventually, the truck wouldn't move more than a few inches at a time. Like I said earlier, when I unhitched, it did much better, (at least I could drive it) but it was extremely weak, even though the RPM range seemed unaffected.

IMHO the trans is shot! What power level did you have your chip set at when towing? Pull any major hills in OD? Trans get really hot?

Hmmm... It should have coded if the trans slipped. Or if the fuel filter was so bad it restricted power.

This may be a stupid question, but have you checked the fluid level in the transmission?

This may be a stupid question, but have you checked the fluid level in the transmission?

Exactly!

Fluid is fine.

I'm off to the dealer in 5 minutes. I will report again once I know something.

Sleeper, I have no chip or mods of any kind. Pure stock.

Thanks,

J.

Good luck and please update once you get back from the dealer. I would like to know what they say when you roll in there with a basically brand new truck whos transmission has given up the ghost.

Update 1pm ET: Just got off the phone with the tech. They were able to duplicate the problem and think one of the components inside the torque converter failed and will call me back once they know more. No specifics at this time.

J.

Unable to reproduce it? Did it start operating normally again before you took it to the dealer?

Update 7pm: Apparently I heard them wrong over the phone. They were indeed UNable to reproduce the described slippage. The truck worked fine for them, but they did not tow with it. They hooked up their diagnostic systems to the truck alone and ran it hard. Everything checked out normal.

GM has asked them to ask me to bring it back tomorrow with the boat in tow. That's right, I will be taking my 31 foot boat to the dealer! They have assured me that if the problem recurs in route, they will dispatch a tow truck immediately. Apparently, and I understand this, GM wants the technicians to hook up the computer while the truck is under tow load and see what the diagnostics reveal then.

I drove it home tonight and it seemed fine, but now I'm paranoid that we won't be able to duplicate it again and I'll be lulled into that false sense of security that it's fixed until it hits me later unexpectedly on the road.

I guess I'll know more tomorrow, but I don't understand why simply unhooking the trailer made the problem go away. Total weight for boat and trailer is less than 8500lbs, and that's full of fuel. Can the truck's ECU "reset" itself once the duress of towing is gone? I wish I understood transmissions better, but I am such a newbie.

Anyway, stay tuned.

could it be when you turned the tow/haul switch off that fixed it

Never had that happen while towing my 14K 5ver. Maybe the trans went into "Limp" then reset when the ignition was turned off? I know that the ECU will reset and codes disappear after the first fault. If the fault occurs a second time, the ECU will store the code.

Go hook up the boat and give it another try to see what happens! If that occurs again, a code should be stored.

Does anyone have a guess what might be the problem?

Do you suppose you may have a brake dragging on the trailer? Try touching each of the trailer's wheels with your hand after a tow to see if all are the same. If one is hotter maybe the drag is causing the tranny to overheat and slip?

9am update.

Well, back from the dealer this morning after thoroughly testing with boat in tow. All systems normal, according to the computer. Truck feels as torquey as ever. I don't know if I'm disappointed that I wasn't able to duplicate the problem. I work with computers for a living, so I understand the sometimes intermittent voodoo nature of digital systems, but this is really perplexing.

The tech's leading theory now is that the tranny's ecms were still "learning" what to do when towing. He told me about the "intelligent shifting" systems that are supposed to fine-tune themselves as you put more tow hours on the truck.

I dunno. Maybe that bridge that we had to ascend immediately after pulling the boat out of the water was steep enough to confuse the ecms temporarily.

Pretty sure it wasn't a trailer issue. The trailer is in great shape and posed no problem to my buddy's 1500 when he came to the rescue.

They installed a funny looking data-capture module that has a button controller on it so that "if" it ever happens again, I can press the button and get the data. GM won't let them touch the tranny until they have data. I understand that, but it's just gonna suck if I have to go roadside again in order to capture that data.

I will say that the service managers and techs were very professional throughout the process. I was pleased with their responsiveness. They seemed genuinely interested because the problem was so unusual. They report very few issues with these trucks. The tranny tech even owned a 2500HD.

I towed about 2 hours today and have a couple longer tow trips coming up, so we'll see what happens. I'm going to be paranoid the whole time, but not sure what else I can do.

Thanks for everyone's thoughts. I will update as events unfold.

-Joe

Joe,

Thanks for the update. Keep us posted on how things go for you on your next long tow.

Good Luck!:)

PS: Please update your sig so we will be better able to assist you if you have any more problems.

Hooligan Joe

Wow!! :confused: That's a very strange problem you have without any trace of something wrong. I would post in the Allison transmition of this forum and see if anyone can come up with a scenario that would fit. With it being new I wonder if there was any residual manufacturing debris stuck somewhere in the tranny and fooled all the elctronics.

Good luck and keep everyone posted

I HATE those kinds of problems! The ones who only rear up while you are in the middle of nowhere, but never at the dealership or when you are looking for them. Good luck with everything, too bad you cannot keep one of their logging tools in the truck so that you could kust hit the button if it happened again and log it for them.

Hey, It does sound like it went into limp mode. Plenty of rev but stuck in a high gear ? I Have had it happen before. But yes could have reset once ignition was turned off.

It was never stuck in a gear. It would actually shift 1-2, but was just crawling a few inches at a time.

They let me keep the data capture module for the next week. It looks like a ****pit ejection button! Hopefully I won't have to press it, but I guess I'll be ready if necessary.

Thanks again,

J.

Hooligan Joe

Wow!! :confused: That's a very strange problem you have without any trace of something wrong. I would post in the Allison transmition of this forum and see if anyone can come up with a scenario that would fit. With it being new I wonder if there was any residual manufacturing debris stuck somewhere in the tranny and fooled all the elctronics.

Good luck and keep everyone posted

Joe,

I would take 1lbz4me's advice and post this in the Stock Allison section. There's lots of knowledgable members that spend time there. Mike L, Joe, and Brayden to name a few. Give it a shot and I'm sure someone will respond.

Thanks for the compliment :D
Sounds to me like the converter flow valve was stuck by a piece of debris. It won't allow much flow into the converter which won't allow it to do it's job. You're first statement has the answer in it.

Well... I have had some experience with a 4 speed Allison behind a 366 Gas engine and have a 2 speed Allison in my loader tractor.

They Both seem like the Torque convertor drains down if you leave it set for a short time. So if you just start it and romp on the gas they don't couple real good untill the convertor refills. I don't know if the new ones are similar or if there was a valve problem causing drain down or slow refilling...

I just figured that was a quirk of the Allison....

Well, things seem to have regressed. Today I left for a one hour tow, but only made it 45 minutes at 60mph on a flat highway before the tranny overheated. I stopped, let her cool down, then made it the last 15 minutes. Just before I arrived, the tranny was running about 210 and the Check Engine Light came on.

I guess it could have been worse, but this is starting to get really frustrating. Back to the dealer I will go, I suppose. At least this time I will have an error code or two, as well as the data that the little button box collected when I pressed it.

Sorry I don't have better news. We'll see what GM let's them do on Tuesday.

J.

Converter flow valve stuck/sticking. Might check to see if there is debris in the pan.