ok, I have recently purchased a '99 50th Anniv Deville. The ONLY code at the DIC is a IPC U1255(Class 2 comms failure). Shifts are all good and smooth, except no attempt to shift up to Fourth and also when manual downshift to Second, the car just "Free Wheels". I have REPLACED the fluid/cleaned scavenger filters, replaced the Lower Valve Body (complete), and Fourth gear servo and piston pin assy. old fluid was very dark, almost black (Rut Roh). Also, NO other codes, checked all fuses(front and back), and the Valet switch is NOT turned on. I am at wits end, please help! Thanks.

 

I think trans will need to come apart, think burnt clutch pack(s) definitely look at 4th gear.

 

I was afraid of that... Can the clutch packs be accessed with the trans in the car? Thanks so much for your help, this thing is making me crazy!

 

yes and no, side cover can be removed and rotating parts removed but it is not the recommended way to do it. some checks can't be done with trans still in car.

 

well, looks like I wont be on the highway anytime soon! Thanks again for your help!