When this happened to me, it was the small switch that gets pressed when my driver side door is closed.(this parts on all the doors). Its a black little switch. I changed it my self, took 5 minutes, cost $4.oo, just had to wait a week for it to come in. I hope your repair is this cheap and easy aswell.

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My Cars
Mercedes CLS
Mercedes C-Class W203 - All time favorite

R.I.P.
Mercedes C-Class - W202 Lemon
Mercedes ML - Warrior
VW Jetta – Worst Car I ever owned - Alot of problems