allison tranny will not shift out of 3rd

[rdbecker]

Started my '06 Silverado 2500HD yesterday,check engine lamp came on and transmission will not shift past 3rd gear. The truck has 50k miles.


Does anyone have any ideas what the problem might be??

Thanks!

Ron

[DmaxMaverick]

That's "limp mode". This time of year, it is usually fuel supply related. Probably due for a fuel filter change, and/or gelled (or water contaminated) fuel. How cold is it, what fuel are you using, and are you using a winter additive (if so, which)? Reading the DTC's (SES lamp codes) will help with more info.