yesterday i changed my rear O2 sensor .. the car seems to be fine but today after driving for a while sudently my (TRAC) light came on and stayed. i sotp the car and shut off the engine then turn the key to on position the trac light came on and then went off. so start the car drove for 2 min then its came back on and stayed again. then after driving for an 1 hour i stop and restart seem to be gone and working while jumping on bump after that it was showing so i stop and start again the trac light was gone .. but the problem is its never seem to be working even when i fall in big hole, the trac light doesnt come and go .. i even drive fast or slow and hit on bumps my self but its never seem to be working ..by the way when i turn the key to on position the (TRAC) light comes on and gose away after couple of minute! so please will you tell me what could be wrong and is it ok to drive like this. thanks for all the help you guys giving me !