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cloe0626, Auto Mechanic
Category: Transmissions
Satisfied Customers: 795
Experience:  was a mechanic in the army for four years and have been working at a dealer ship the past five years
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Dear I have Sierra 2001 8.1L automatic transmission Allison

Customer Question

I have Sierra 2001 8.1L automatic transmission Allison M74
My problems is the transmission not engage in R-D-3-2-1 I was changed switch neutral safety ACdelco D2256C and nothing changed then I bought error scan tool and I found to errors:
1- P1721 transmission solenoid B controlled clutch engaged
2- P0700 transmission control module (TCM) requested MIL ILLumination
What can I do?
Submitted: 1 year ago.
Category: Transmissions
Expert:  cloe0626 replied 1 year ago.

its a error in the transmission control module it may need to be replaced but i would try having it reprogrammed first

Customer: replied 1 year ago.
this code P1721 transmission solenoid B controlled clutchengaged