: '05 STS Tranny Problem

Johnny C
03-03-07, 07:57 PM
"05 STS V-6 new - transmission shifting first 21,000 mi smooth/silk !

harsh shifting 2-3, 3-4, 4,5 at 24,500 mi

dealer has tried software revisions - same symptons !

has anyone had or heard of shifting problems ?

how is this problem corrected ?

Johnny C

03-05-07, 05:01 AM

Curious George
03-07-07, 02:04 PM
I have an '06 Northstar STS with 27,000 miles on the clock. Just this past week or so I've noticed occasional harsh shifts, mainly downshifts while gently decelerating to a stop when the transmission is cold. I have a service appointment Tuesday and will discuss it with the service writer. Meanwhile, I'm paying close attention so that I might more precisely describe the problem.

My understanding is that shifting is controlled by the powertain control module which lifts the throttle momentarily during upshifts and blips the throttle during downshifts. At the drag strip last Summer and Fall I could feel the throttle lifts, even in sD mode. The 3-4 upshift at about 85 MPH is particularly langorous and smooth, and therefore troublesome for someone trying to increase 1/4-mile terminal speed, coming as it does just before the traps. (I achieved 14.521 seconds @ 94.1 MPH in November when the ambient tempurature was about 60 degress F.)

03-09-07, 04:04 PM
There are some other threads on here that address the problem. I had the same thing on my 05 V8. It was a simple software fix for the TCM at the dealer. Look for the other thread that actually has the TSB attached. My service copy says TSB 06-07-30-030. It shifts like a brand new car now.

03-09-07, 06:57 PM
One of the problesm I am having with my '06 Lucerne is the transmission shifting sluggisly. Of course, that is a 4 speed THM and the STS is a 5 speed. How similar are these transmissions?