Cadillac Repair: speed sensor/transmission, cadillac seville sts, cadillac seville

Question
I get a message Service Transmission, and Service Engine light goes on. They tell me at the dealership that it is a speed sensor that senses the speed and then trans shifts. Is this a minor or major repair?
What should this work cost?
My car is 1996 Cadillac Seville STS 138,000 miles.

Answer
Hi Michael, Without knowing the code(s) it makes it tough to give the correct advise. If its the speed sensor I am thinking of alot of people don't bother to get it fixed because the trans has to come out and disassembled. Around $700 seems to ring a bell but you will need to check with the service writer and maybe some trans shops for price quotes. Bill