I have an intermittent fault on my 2001 LS V8. Message reads Check Traction Control and abs/traction/brake lights come. It also shuts down the power steering. Auto parts store read code and said front and left wheel sensors missing. Took it into shop to replace wheel sensors. They road tested and it was reading 25 mph faster than it was going. They think it is a control issue and they are not set up to deal with that. He said he can't believe that all 4 sensors are bad. Any ideas?