Hello,
I have a 2005 MCS and been able to find posts with similar problems and solutions as my car, but not the same symptoms. My car goes into limp mode with the Check Engine Light, TPMS Light, DSC light and EML light all on. I turn off the car and turn it back on, and everything goes away except the check engine light. I can drive the car for about a day or two, in this time the check engine light goes off, and then it happens again. It seems to happen only while I'm cruising at a steady speed. It throws the P0642 code, which is a general voltage low code. I replaced the bypass valve thinking that was the problem, but it's still happening. Mods I have are the 15% pulley, Alta cold air intake, and Milltek Catback exhaust. I also have a boost gauge and had to tap into some wires, I was wondering if this could be a potential problem? Any input would be greatly appreciated. I just really want my car to be reliable again.

 

Mine is always the gas cap needing tightened.

 

Could be a wheel speed sensor or a knock sensor issue. Some simple things is to disconnect the negative battery terminal for at least 15 minutes. Can also remove and replace the DSC fuse.