check engine light

Had my rear brakes repaired, and the sensor was damaged. Left for a trip, and the "check brakes" was coming up on computer. Did about 300miles, and when slowing down in a city, my car went into "limp home" mode. Got to a Mercedes dealer, and they said a coil was needed-$335.00 repair. While at dealer, my husband purchase the brake sensor, but did not install. Traveled 900 more miles, and when we restarted the next morning, the car was making banging noise like a missed piston, and was lacking power. My husband took to Advanced Auto, and they checked the computer(?)and said it read 3 coils needed repair. He installed the sensor to the brake, and the car was back online, peppy and no noise. On the return trip about 600 miles into it, the SOS-VIST WORKSHOP liight keep coming on and offl, and the compute read 1 malfunction.but the car ran fine. When we hit 900 miles, the check engine light appeared and at 1100 miles, the car was hesitating at stops.
Mercedes benz 2003, C240, 49000miles 2wheel drive