I have a 1989 300se. The first time I step on the brake pedal after starting the car the check engine light comes on and won't go out until I turn the car off As long as I don't step on the brake pedal the check engine light will remain off. I have driven down the interstate for 1 hour without stepping on the brake pedal and the check E L stays off.As soon as I exit the interstate and apply brakes the light comes on and stays on until I turn the car off.I restart and once again no check engine light will come on until I hit the brake pedal. Has anyone encountered this problem before? I placed the post also on Mercedes forum with no luck yet. thanks again.