Is there something wrong with my Allison?

I recently went to Texas from Minnesota. The truck ran well, except through some hills in Missouri. I was empty, going 72 mph, going up a big hill and my allison went into limp mode. Since I wasn't hauling anything, I didn't have it in tow mode. I immediately knew what had happened. Pulled over and restarted the truck. I didn't have any issues at all for the rest of the trip. Is this a sign that some previous owner abused the allison? Or maybe something easier, such as a slightly plugged fuel filter? Any experience out there with this problem? Thanks!

Why not take it to a Chevy Dealer and see if they can pull any codes for the transmission ? Better safe than sorry.

the SES didn't come on when it went into limp. Is it possible it still stored codes? If so, I have an OBD-II scanner... If I can figure out where it is! Otherwise, is it too intricate for my standard 100 dollar obd-II scanner to detect?

If there are codes they should be in memory. I do not know the full potential of these inexpensive OBD II scanners. We use a Solus and MT-2500 in our shop.

Can't hurt to try yours.

I just checked and there are no codes present in history. Is it possible it didn't go into limp mode? I was driving along at about 72 or so up a sharp, steep hill and all of a sudden it pops out of cruise control the rpm jumps up and it starts losing speed fast. I think I stepped on the pedal and I limped it into kansas city at about 60 MPH, and if I tried to give it much pedal it acted like it was coasting again and the rpm went way up. I pulled over, did a restart and all was good. The trans temp was barely off 100 degrees and the fluid looks fresh. Is there anything else it could have been?

There is a "Grade Braking Algorithm" for steep down hill braking that the transmission will go into to save wear and tear on the vehicle braking system not sure if maybe something happened there going uphill.

Also possible it is not the transmission but the cruise control ?

Unfortunately that is about all I can think of.

Yeah it was strange. I turned the cruise off as soon as the engine revved up to 3k. It continued to act strange until I turned it off. People are saying the fuel filter can cause some problems, so I'm going to change that and stomp on it to see if I can get it to do it again. Otherwise when I was in the hills after I restarted, I threw it in tow/haul mode to be safe. On the way home, I didn't do anything special except maybe drive a touch slower. So the question remains, can the tranny go into limp mode and not set a code??

Update: Changed the allison filter / fluid last night and finally did an scan check. There are absolutely no codes stored! Does the allison computer throw a code when it limps? Could it have been something else?

Update: Changed the allison filter / fluid last night and finally did an scan check. There are absolutely no codes stored! Does the allison computer throw a code when it limps? Could it have been something else?

I'm no expert on this transmission but you had the vehicle in cruise control and the engine rpm's rose...this is a transmission problem..also you will need a DTC scanner that can read drivetrain codes...

most of the scanners read only engine codes...read the spec of the code reader for its capability...

Turns out my problem was a clogged fuel filter. I took it in to the dealer and had their diesel tech hook it up to the tech 2 scanner. There were no allison transmission codes stored whatsoever, and only a loss of fuel pressure under the heavy load showed up on the scan tool at the same time and speed as when I thought I limped it.

Turns out my problem was a clogged fuel filter. I took it in to the dealer and had their diesel tech hook it up to the tech 2 scanner. There were no allison transmission codes stored whatsoever, and only a loss of fuel pressure under the heavy load showed up on the scan tool at the same time and speed as when I thought I limped it.

I thought you already replaced the fuel filter....so the new filter you put in plugged up already...

I would cut open the filter to see whats going on in there..

I turned the cruise off as soon as the engine revved up to 3k. It continued to act strange until I turned it off. People are saying the fuel filter can cause some problems, so

That is the EXACT same thing that happened to my gas 4.8L engine about 50 miles before my fuel pump died in the AZ desert. My Cruise was on too @ the time.

Hope it helps someone else!

-TD

I replaced the fuel filter when I did the tranny filter last weekend. Prior to that, it hadn't been changed in a while, I ascertained. When I pulled the old filter off, there was a little bit of particulate sediment that came out when I emptied it. Regardless, the tech 2 scanner showed that a clogged fuel filter restricted fuel flow when the truck cut out up that big hill in Missouri. Since I changed the filter, I notice the truck has been getting stronger every time I drive it. Now I can actually drag my friend with the 6.0L Chevy Express van and win. haha. And now it runs more smoothly as well. I'll keep my eye on it, and I should heed the advice to keep an extra one handy at all times in the event of a failure. It should be noted my pocket OBD-II scanner did not pick up this code; only the tech 2 scanner at the dealer picked this one up, so I can see this being one bear to troubleshoot on your own. Thankfully it's something you can change in 15 minutes!