The service 4wd system warning has just come up on my car too, along with the traction control light. The car was driving perfectly fine, I parked the car and turned it off when I returned a few hours later and started the car the service 4wd system warning came up. It seem that the rear electronic controlled limited slip differential is now locked all the time(the car requires allot of throttle to turn tight and you can hear the wheel skidding ) I plugged in the scan tool and it seem pretty much every control module aside from the transmission cannot communicate with the ECM, I checked the diff control motor with the scanner too and everything seems ok. As a result FCC is now deactivated along with traction control and Cruze control it also seems like it is not transferring as much power to the front as it normally would. Very strongly feel it’s just a faulty sensor . Anyone know which one/ones it may be ?