Allison 5sp: Limp Mode after 5 Seconds in 1st

[Jason Douglas]

I humbly submit this request for help to a knowledgeable group of individuals.

2003 GMC Top Kick C5500 w/ Allison

Problem: When vehicle is started and placed into drive the trans will shift into first gear for around 5 seconds and then slip into limp mode/3rd gear and remain there.

So far: No codes or dash lights. Read with reader and again no codes.

Again, I humbly request your help.

 

[Mike L.]

Code reader won't cut it. You either need Allison DOC on a laptop or a Tech 2 to read codes.