I have a 2007.5 Chev Max LMM automatic 20K mi. My truck is currently in Chev shop for this problem and they haven't been able to fix it and are consulting with GM engineers higher up.

Problem: It occurred when I was backing out of the garage (forgot something inside the house) put it in park (instantaneously) and then back in reverse (thought it was not good to leave truck half way out of garage) - The nightmare ..... The truck started reving in reverse with my foot on the brake (No, Mr Toyota, my foot was not on the throttle!).:eek:

I took it to the GM dealer and we were able to reproduce the same thing by shifiting from reverse to park and back to reverse very quickly. The motor revs in reverse.:(

Dealer changed CPU and checked all associated sensors. Problem still exists. Now they want to replace the torque converter???????:confused:

Has anyone else heard/had this problem? Have a fix? Can you duplicate it on your truck of similar make/model?? :D

Thanks for you interest:cool:

So it has done it again after the changed ECM?
Never heard of this here but not search here for anything like that either. Have you tried the search tool to see if there is any related post?
No codes ever thrown? If some then what?
Never had this issue myself.

Ok is the truck totally stock? meaning no mods, tuners, aftermarket products or electronics installed. No matter how small or meaningless post it.

I do not see the torque converter as an issue. I would try to use a logging device to monitor different PIDs of the ECM, TCM, and maybe the BCM. Don't know what all happens on the BCM. Basically black box logging and see what is going on at the time it does happen. I do not know how well a GM Tech II logs this data and if it log all at the same time. Best I can say is using a Flashscan V2 and either can be logged right to the device or using a laptop and the EFILive scan software to record different PIDs. Then when it happens see what things like the APP_d which I believe is the drive by wire fuel pedal input as an example. I suggest GM log your truck to find the problem. Or maybe post your area your from and maybe someone in the area may wish to help you out.

Brian

Weird, never heard of that in my couple of years here and there! I definitely don't think it is the torque converter either....

So my dad posted this for me. The truck is a 2008. Has 20,000 miles on it. The only mod done to the truck is i had the muffler cut off.....(hoping it would make it louder). The dealership has done all the pulls with their computer and have now resorted to talking with the engineering crew at GM. GM claims this is the first truck in the nation to have this problem. The first time that it happened the truck basically powerbraked in reverse. the second time it acted up the truck idled very roughly but did not idle up, shook the whole truck, and the third time it throttled up again. The GM engineers had them swap out the ECM and that did nothing. After waiting for 2 days to get a response from the engineers they said to change the tourque converter. Something about an electrical solenoid may have fallen of of it???? I am mechanically savvy and this comes as a shock to me to change a tourque converter for an electrical issue. Thoughts???? I am at a loss!!

Replaced the Torque Converter and still a problem...........Told the next step is to fly a GM Engineer out to take a look at it. Maybe I have a "Lemon"!!

Very interesting....keep us posted on what you find out.

Where are you located?

I have a 2007.5 Chev Max LMM automatic 20K mi. My truck is currently in Chev shop for this problem and they haven't been able to fix it and are consulting with GM engineers higher up.

Problem: It occurred when I was backing out of the garage (forgot something inside the house) put it in park (instantaneously) and then back in reverse (thought it was not good to leave truck half way out of garage) - The nightmare ..... The truck started reving in reverse with my foot on the brake (No, Mr Toyota, my foot was not on the throttle!).:eek:

I took it to the GM dealer and we were able to reproduce the same thing by shifiting from reverse to park and back to reverse very quickly. The motor revs in reverse.:(

Dealer changed CPU and checked all associated sensors. Problem still exists. Now they want to replace the torque converter???????:confused:

Has anyone else heard/had this problem? Have a fix? Can you duplicate it on your truck of similar make/model?? :D

Thanks for you interest:cool:

So when you say it "revs in reverse" do you mean that the engine RPM increases (seen on Tachometer) or just that you have to press hard on the brake to hold it back because its fueling to maintain idle speed?

If the RPMs are increasing, how high does it go?

If its carrying a lot of torque in Drive and Reverse, while stopped with your foot on the brake... that's a sign of a failed stator one-way clutch in the torque converter. Which would agree with the original diagnosis.
Q1: Did they install a new or Reman Torque Converter? Post the part number if you have it.
Q2: Was the one that came out discolored by heat?

I am located in Denver.

When this happens the RPM's Increase to between 1800 and 2200. It only happens when you go from reverse to park and back to reverse very quickly. To me it does not seem like a case of excessive tourgue, it is mearly the throttle being applied on its own.

When this happens the RPM's Increase to between 1800 and 2200. It only happens when you go from reverse to park and back to reverse very quickly. To me it does not seem like a case of excessive tourgue, it is mearly the throttle being applied on its own.
A failed stator clutch won't let the engine rev over about 1000 RPM so not likely the TC.

So a R - P - R causes the issue? To duplicate it do you have to be rolling in the first R before you go to P or completely standing still? Level ground? Hill? Any tempature relation?

I assume this is the first time it happened?

R-P-R on level ground standing still. It has happened several times now from them duplicating it. But after the first time it happened I took it right in.

Just got a phone call and the latest is to bypass the transmission cooler line and see if that fixes it and then if that does not work they want to bypass the entirre cooling system past the radiator and and see if that works. Then after that doesn't work they want to replace the transmission pump. I just had a very stern conversation with the service manager saying it seems crazy to me to look at the transmission cooler lines for a problem with the truck applying throttle on its own. Very frustrating.

Thanks to all who are posting. It at least keeps me a little sain!! :)

Look up a lemon lawyer in your area right now and get a hold of them. It is a good thing you seem to be mechanically savvy. The wrong person behind the wheel this could cause some serious problems. I'd say if they keep jacking around trying stupid things to fix it to get it lemoned and tell them to shove the truck up their rear end.

you need to ask Mike L. in the tranny section, maybe he has heard of this before.

My God what crazy things they are doing. At least to me it is crazy. So a signal is being sent from the TCM to the rest of the modules is the way I am seeing it now. I have not check but anything related to the shifter is only related to the Allison and TCM. If it is something that can not be monitored with a scanner then I guess I try a new TCM first. Then replace the wiring harnesses. Then last the Allison itself. If it still happens the LEMON it for sure.

Brian

As much of a possibility for danger/ injury as this presents, I'm surprised that they haven't taken ownership of the truck and got you into a brand new one by now.

I would expect they would want this truck back at GM not a dealership - both to determine the cause of the problem and to keep it quiet.

What is lemon law/ product liability for something like this past the first 12 mos? I would expect GM would have full liability if someone were hurt or killed due to this happening.

Sounds like it's attempting to rev match the internal "output shaft" speed, which is obviously zero. The fault lies in the transmission's signal generated to the PCM as I can envision no scenario wherein the sensor itself could generate the appropriate signal (rust, crossed wires, etc).

Take any allison truck down the road at freeway speeds and shove it into neutral. It will command the engine to remain at the previous RPM (rev-match). I suppose it would be possible to have corrosion right at the modules plug, or chafing where it approaches the output shaft sensor.

Im thinking the same thing as heymccall

[quote=jon5212;3736172]Look up a lemon lawyer in your area right now and get a hold of them. It is a good thing you seem to be mechanically savvy. The wrong person behind the wheel this could cause some serious problems. I'd say if they keep jacking around trying stupid things to fix it to get it lemoned and tell them to shove the truck up their rear end.
AGREED!

I doubt its a trans speed sensor signal problem, or you'd see more problems in other gears.

The TCC makes some sense to change because of a possible stripped stator, and the cooler bypass as a clogged cooler or kinked hose could put extra load on the engine by not holding the LU clutch off, but I struggle with the oil pump... and none of these should cause an increase in RPM.

The Duramax has a strong idle speed control and is able to make torque to overcome load at idle. Like if you're messing around with the TCC solenoid "F" while stopped and bring on LU, it can fuel up and smoke a clutch. So the engine is probably somehow overreacting to the load being placed on it when you go to Reverse, but only R-P-R?
It seems too isolated to be a main problem like speed sensor.

Does it rev up for long? What makes it stop?

Does it slip in Reverse or take a long time to make the shift into R?

i would have the dealer log all the trans functions that they can. sounds similar to what my truck was doing when the internal trans harness had a short in one of the connectors. mine would do it if shifting from d to p and it would lug the engine down then rev to about 1400 then settle back to normal idle speed after 3 or 4 seconds. a continuous rev seeems very odd with all the input that the ecm requires for that to happen.

I have finally convinced the service manager to leave the tranny alone and focus on the electrical. I asked the SM why they were focusing on the tranny and he said that when they took the computer snapshots from the truck when the truck was acting up and sent them to GM the only thing that the engineers could see was that there was abnormal pressure in the tranny and the transmission was slipping. I very vocally told him, "Dude, of course the tranny is slipping you are power braking my truck in reverse" and then I told him that he needed to get a field engineer to come look at the truck because the problem that the engineers are trying to solve and the problem the dealership is trying to solve are clearly not the same problem. He agreed with me and did not think the tranny is the prob. He made a phone call and about an hour later I got a call from him saying that the engineers NOW dont think it is in the tranny they think it is something electrical or a programming error.

When this happens the truck idles up to about 1800 RPM for about 3-4 seconds and then goes back to a normal idle. The transmission seems to be functioning properly as when it throttles up, it is fully engaged in reverse, no clunking or odd sounds from the tranny.

Now I get to wait until next tues for a fix as the engineers are off for the weekend and they will begin to look for a solution to the problem on monday.

Another joke.........trying to get a rental vehicle throuh GM........Long story but I am now driving a GMC Acadia after being offered a Ford Focus!!!!! Are you frickin kidding me!!!!!!

As much of a possibility for danger/ injury as this presents, I'm surprised that they haven't taken ownership of the truck and got you into a brand new one by now.

I would expect they would want this truck back at GM not a dealership - both to determine the cause of the problem and to keep it quiet.

What is lemon law/ product liability for something like this past the first 12 mos? I would expect GM would have full liability if someone were hurt or killed due to this happening.


Agreed, I am working on finding out the details about the Colorado Lemon Law!!

Did you have the fast idle feature activated?:confused:

Did you have the fast idle feature activated?:confused:

Possibly, could this trigger something. I pulled it out of my garage and i specifically remeber looking at the temp and it said 47 degrees. not cold enough to activate the elevated idle.

Agreed, I am working on finding out the details about the Colorado Lemon Law!!

Go here: http://www.bbb.org/us/Storage/16/Documents/BBBAutoLine/CO-LLaddinfo.pdf

Basically you need to contact the BBB. They will act as a mediator between you and GM to work out the settlement.

Good luck and PM me if you need more info. Went through it in 2007 to get rid of my lemon, which incidentally had electrical problems that the dealer and GM TAC couldn't figure out.

Go here: http://www.bbb.org/us/Storage/16/Documents/BBBAutoLine/CO-LLaddinfo.pdf

Basically you need to contact the BBB. They will act as a mediator between you and GM to work out the settlement.

Good luck and PM me if you need more info. Went through it in 2007 to get rid of my lemon, which incidentally had electrical problems that the dealer and GM TAC couldn't figure out.

Come on now guys... Give them a chance to fix it. Lemon laws are to protect the consumer IF the company cannot fix something. As things go the service dept. and GM TAC are working down a trouble tree and it sounds like they're moving away from the hardware parts doing more electrical troubleshooting. I realize its frustrating (it took my dealer a week to fix my rear defroster!), but it is just surprising how many are jumping on the lemon law. I'd save my effort and undue stress for now and wait to see what happens next week when the engineers can take a closer look at it!

I say the same to give them some time but you do need better compensation than the go kart they have given you.

Brian

update.......Allison Engineers have taken a look at the Tech II data and think they have found the problem in the tranny. Going to replace the Tranny and the TCM and hope that fixes it. Service manager told me it has something to do with pressures in the tranny. I am hoping that this fixes it. Tranny wont be in until next monday. Update after it is installed.

Come on now guys... Give them a chance to fix it. Lemon laws are to protect the consumer IF the company cannot fix something. As things go the service dept. and GM TAC are working down a trouble tree and it sounds like they're moving away from the hardware parts doing more electrical troubleshooting. I realize its frustrating (it took my dealer a week to fix my rear defroster!), but it is just surprising how many are jumping on the lemon law. I'd save my effort and undue stress for now and wait to see what happens next week when the engineers can take a closer look at it!

I agree he should give them a chance to fix it. I also gave my dealer six weeks to fix my 2006, and they couldn't do it. I pissed around way too long trying to "negotiate" with GM about some kind of resolution to either fix the truck or give me a new one, and got nothing but a frustrating, aggravating run around. When I invoked the BBB process, it was settled in a week.

He asked the question - I gave him the answer. If he needs to go down that road, the sooner the better IMHO...

update.......Allison Engineers have taken a look at the Tech II data and think they have found the problem in the tranny. Going to replace the Tranny and the TCM and hope that fixes it. Service manager told me it has something to do with pressures in the tranny. I am hoping that this fixes it. Tranny wont be in until next monday. Update after it is installed.


Hopefully that fixes the problems you're experiencing. If it does, conclude with them that you want a no-charge 2-year 24000 miles extension on your bumper-to-bumper warranty << for all your trouble and their several misdiagnosis.

Could not pin point the problm but just replaced the transmission and it is fixed. So i got a new tranny. Not so bad i guess. All GM would offer me was a 12 month lube, oil, and filter plan for free. Not really any use to me as I run Synthetic in my truck. Just glad to have it back and working.

Glad you have it resolved. be nice to get a little something else but at least it is fixed.

Brian

im not sure how a mechanical trans problem could cause this issue though?

Could not pin point the problm but just replaced the transmission and it is fixed. So i got a new tranny. Not so bad i guess. All GM would offer me was a 12 month lube, oil, and filter plan for free. Not really any use to me as I run Synthetic in my truck. Just glad to have it back and working.
im not sure how a mechanical trans problem could cause this issue though?
update.......Allison Engineers have taken a look at the Tech II data and think they have found the problem in the tranny. Going to replace the Tranny and the TCM and hope that fixes it. Service manager told me it has something to do with pressures in the tranny. I am hoping that this fixes it. Tranny wont be in until next monday. Update after it is installed.
I would guess it was a faulty TCM (not the transmission itself) sending bogus torque requests. I.E. Put it in reverse, park, reverse, and the TCM asks for 400 ft-lb, causing the engine to rev up to provide the requested torque.

As to why it was sending bogus requests, who knows. Odds are, the GM/Allision engineers who got your original TCM will have it disected and figured out, but the public will never know. Don't want anyone thinking GMs share the Toyota problem.

Just my $.02. Glad you got everything working though!!