My Deville has 150K miles. Recently, when starting the car after sitting overnight, the speedometer does not work on occasion. Also, the car makes a thud when I shift it into drive when this situation occurs. This has happened twice and has corrected itself-the speedometer will work and the transmission will shift smoothly. I get the feeling that something bad is about to happen. Anyone have any ideas on what the heck is going on??
Thanks!!!

 

Always helpful to see if there are any codes. Do you know how to obtain the codes from the DIC?