Limp Mode

[kjjz28]

I'm new to the Duramax/Allison arena (just bought my '02 a month ago) and have seen some conversation about the Allison transmission going into "limp" mode. What causes this and how do you prevent it? I presume the SES light will come on or give some type of warning. In the absence of the warning light, how can you tell if the tranmission has done this? Thanks!

[BBSilverado]

limp mode or "reduced engine power" mode is on all the NBS engine and tranny configurations and has nothing to do with the Allison tranny.

The vehicle will go into this mode when there is a problem with the engine such as high coolant temp, a bad sensor, low voltage, etc.

[_nar_]

Allison limp mode: Basically if you add more power than the clutches can take it slips, tcm detects the slip and shuts you down. It usually drops to 3rd and won't rev over 2000. You have to shut the truck off and let it sit a couple minutes to reset. After you do it once it will do it more easily. A duramax can safely have about 60 hp added to it, more than that and you risk slipping 5th gear when you hit the 4-5 shift at WOT. Some guys get away with more. Especially if they let up on the 4-5 shift.

Check out the forum at www.thedieselplace.com for more info, read back a bit on the transmission forum or do a search, you'll learn a lot.

[vhato]

Limp Mode has been in ALL GM Electronically Controlled Automatic Transmissions since 1993.