My vehicle is a 2005 Impala LS with 3800 v6, 81000 miles. When it was parked on Saturday all was well. When I started it on Sunday morning, the "TRAC OFF" light and "ABS" light remained lit, and the chime bonged like crazy. The message display showed "Service Traction System". The CEL light goes off shortly after engine start like it normally would. While driving on the highway, all seems normal except for the "TRAC OFF" light and "ABS" light being lit (chime stops after about 15 seconds, and message center goes blank after about 60 seconds). No anomalies noted when braking, though I haven't braked hard enough to engage the ABS. A local mechanic hooked up a code reader, but it indicated "No codes". The only work done recently was changing the snow tires for summer tires, done in my driveway 3 weeks ago. The dash was dis-assembled a year ago to repair the instrument cluster (replaced stepper motors). Last fall the local GM dealer replaced the heater core, though it turned that the condensation on the inside of my windshield was not coolant as they said it was (never going back there!). The car has not been driven by anyone but myself, and that has been on paved streets around town. Nothing hit that I know of that might have damaged anything under the car. Any ideas on what to look at? I am considering dis-assembling the dash to check the TRAC OFF switch, and removing the wheels one at a time to see if anything looks out of whack there.