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I am new to the diesel world and have heard nothing but good things about the allison. I have been about all sorts of things and keep seeing the limp mode. Can someone explain it to me, what it does, how to avoid it, what to do if it does happen? Thanks
 
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Limp mode is when the TCM senses slip in the transmission and locks it into a single gear to avoid further damage. The other limp mode is reduced power mode and is when the ECM feels something is out of whack and reduces engine power to avoid further damage.

Both can be avoided by leaving the thing stock but that’s no fun so when it dose happen you simply pull over and turn it off for 30sec for trans limp or until its cooled down for engine limp. If you have a flash programmer you can also go in and clear any codes it threw or they will clear on there own after three drive cycles without the problem accruing again.

There is a much longer expiation then that but you get the idea… oh and every time you limp your trans it makes it easer to do it again.
 

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And just so you know the cycling the key thing isn't always a guaranteed fix so I would highly suggest getting a flash programmer that will read and clear DTC's. We have many great vendors on here to choose from.
 

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If you ever hit transmission limp mode on the highway or track or wherever, quickly toss it into neutral right after you feel it and it will prevent it from throwing codes or locking into a gear, i figured this out after about the 3rd time i limped it, then when i was on the track 100ft before the 1/4 mark it would hit limp mode so id toss it into neutral, worsened my times forsure but best i can do till i get a built transmission. Hope that helps somewhat lol
 

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If it keeps going into limp mode every time I tow,what would be the solution?
Depends on what limp mode set the "Limp". Fuel, FPRV, Engine Miss, Trans, speed sensor and etc. So without the code, it is just a guess-!!:nerd:

If it is a trans code-- it will usually show P0700-[which turns on the fault light]- there are always other codes with the 700, but cheap code readers will not show them.

Post the codes-!! :grin2:
 

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I have a 03 Silverado Duramax with the allison transmission.

Today it went into limp mode and and would not go forward or in reverse. It was if it was in neutral, but when i cleared the codes (did not wright them down) it was fine again. This has happend a few times the last months, and it`s always when the transmission/oil is cold/right after start this happens.

Anyone have an idea what could be wrong?

It has driven 164 000 miles right now, the was changed in march 2015.

I changed the nsbu switch on the side off the tranny a few years ago since it did not show which gear i was in on the cluster.

Im sorry for my bad english but i leave in Norway and we do not have so much off these trucks here, so thats why i need to ask here since there is not much knowledge about these transmissions here.
 

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Like noted above, we need the codes.

Low fluid-- water in the NSBU switch-- just a guessing game without the codes.

If you have a Android phone-- [does not need to be active] you can buy a Bluetooth OBDII adapter [$15], and down load Torque Pro-[$5].. You can read a lot of the operating parts, and clear codes.
 

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Like noted above, we need the codes.

Low fluid-- water in the NSBU switch-- just a guessing game without the codes.

If you have a Android phone-- [does not need to be active] you can buy a Bluetooth OBDII adapter [$15], and down load Torque Pro-[$5].. You can read a lot of the operating parts, and clear codes.

Got some codes yeasterday.

TCM P0846
PCM P0700
UNK P2645
 

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A list of mods in your sig might help as well. If you're towing with a tuner cranked up, well... that would explain some things.
 

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one time last year when it was around zero degrees I started my truck and put it in reverse and it didn't move. I put it in park and let it warm for a minute and then it went into reverse. must be a safety feature.

good information on this tread , thanks guys
 

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A list of mods in your sig might help as well. If you're towing with a tuner cranked up, well... that would explain some things.
This only happens after cold start and im driving out and stop at a stop sign/red light and the truck is just at idle in drive.

I have never experienced this when it is warm.

I have efi live (80hp tune), 4 inch exhaust, 3 inch downpipe, K&N filter and a boost valve.

So this has never happended while towing since my trailer is parked a few miles from where i live, so i got some temperature in the engine/tranny when i start the tow.
 

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If the converter drains down after it sits overnight, [Converter-Drainback] , it may be caused by bad seals or worn pump/bushing. When you start it, let it run about 30 seconds before you put it in gear- that will refill the converter.
 

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Depending on the ambient temps, the trans will lock itself out and throw a code if you try to put it in gear until it has a chance to warm up. It was -20 here and I had the truck plugged in but didn't have the trans pan heater on it yet. Truck fired right up and the water temps were about 70 degrees. I went to back out, but the trans coded, the temps were -15 and it wouldn't move till it idled long enough for the trans temps to reach above zero.
 

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I put my 03 GMC DMax in reverse back up put it in drive without mashing the accelerator and about three seconds it goes clunk and yhen a harder clunk and that my friend is limp mode all i got it fourth, reverse , and neutral , park, has anyone ever ran into this kind of aggravating crap...
 
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