When I first bought the Silverado we went to Lake Tahoe, elev. 8000 ft and when decending, the Allison grade braking feature worked great! A tap of the brakes would slow us down to 15 or 20 mph and keep us there until I had to hit the accelerator. A trip to and from Oregon last year showed that the grade braking feature was working OK.





Recently, in shorter, more curvy, 3000 ft elev. mountains, the feature does not work. We are upshifting, not downshifting. I have tried hard, stab braking and slow, steady braking. I have tried in T/H and out of T/H. It's not working.





I've read all the Allison website info, Q&A, TSB's, etc. and can't figure it out. Went to my selling dealer who does not have an Allison tech on site. They looked for codes, allegedly, and found none. They suggested disconnecting the battery for 15 minutes and reconnecting. Then go into the mountains and supposedly the grade braking will come back. I have some doubts about this. This would affect the truck's computer and maybe I would see the "check engine" light come on. I found another dealer who has 3 Allison techs and will be off to see them in the future.





OK, does "adaptive learning" have anything to do with this? If I drive 100 miles on the freeway and then go into the mountains, I would think the Allison would recognize this and the grade braking would activate real soon. Could it be as simple as a loose wire or connector which runs between the brake electronics and the TCM?





We carry a 4000 lb. slide-in camper in the bed.





Any thoughts, please, before I visit the other dealer with the Allison techs?








Edited by: Scooter

the allison would set a code if it farts. Grade braking is more pronounced in T/H. Have yet to see one with you concern, Its electrical thing more then likely if its not working...wierd....http://www.dieselplace.com/forum/smileys/smiley5.gif

If you have a the juice it seems to take away from how well the grade braking works. Just a thought.

Thanks for the two replies. No Juice, I am stock.


Anyone want to chime in about the "adaptive learning" feature?


Could it be I am not applying the brakes correctly? Not likely. All you do is tap the brakes while going downhill and the downshifting begins.


I have tried coming to a full stop at the top of a grade and after gaining speed tap the brakes and/or mash the brakes. Nada.


Sometimes the most obvious boo boo is not apparent. What, exactly, is your procedure for activating grade braking?

If you figure out what is making it not work, let me know. I hate that "feature" since I don't tow much....



If someone could figure out how to make it switchable on the 01-03 trucks, a kit would sell....

Scooter,



I have an 04.5 LLY, so I don't know if it is different than yours or
not, but when I have tow/haul mode selected, I usually very lightly
ride the brakes until the transmission downshifts, then I take my foot
off the brake pedal. If I want it to kick down another gear, same
story, ride the pedal until downshift then take my foot off.



If I don't have tow/haul selected, it will auto downshift like grade braking from 5 to 4 but for no other gears. . .



Dennis

One thing you may want to check out is your accelerator pedal position (APP) sensor. Since these trucks are "fly by wire" the accelerator pedal is connected to a large rheostat that sends an APP signal to the ECM. There is a history of misalignment and adjustment on the APPs and the signal can also be affected by floormats. This appears mostly by not getting 100% throttle signal when trying to reset the "change engine oil" or an edge. However, the reason I bring this up is that there is a "zero throttle" input (as well as brake applied) to the TCM that controls downshifts and grade braking. If your APP is showing too much signal at the bottom it may be affecting the decision to grade brake.