Tech Tip: What to do if your Mercedes Benz right front headlights are inoperative

Vehicle: 2003 Mercedes Benz E320 Sedan (211.065), V6-3.2L, Automatic Transmission

Mileage: 262,396

Problem: The high and low beam headlights were out on the passenger side. Because of the vehicle’s age, the owner decided to replace all four headlights. Unfortunately, the passenger side high and low beams were still inoperative. He brought the car to the shop for a diagnosis and repair.

Details: The technician connected a scan tool, which revealed no diagnostic trouble codes. Next, the technician verified that there was no battery power to the passenger low and high beam headlights. At that point, he called ALLDATA Tech-Assist for advice. 

The Tech-Assist consultant suggested starting by inspecting fuse #75 (40a), which is in the front pre-fuse box, mounted in the passenger footwell. Since the fuse checked out good, the consultant suggested verifying that the passenger signal actuation module (SAM) control unit was getting full battery voltage on terminal #5 (red) and that terminal #1 (brown) was getting a solid ground at connector I1. Both power and ground checked out perfectly.

The next test was to check terminal #6 (yellow) for battery voltage on low beam and terminal #2 (white/yellow) for battery voltage on the high beam at connector I3.

While testing those wires, the technician noticed that if he removed the SAM control unit bracket, the lights would work and when he tightened it back down, the headlights would lose power.

Upon closer inspection, he found the yellow and the white/yellow wires were both open under the floor panel. The SAM control unit harness was a little short and was being stretched, which caused the wires to break inside the insulation.

Confirmed Repair: The technician repaired both wires and rerouted the harness so there wouldn’t be any tension on it. After the repairs, both passenger headlights operated normally.

 Information provided by ALLDATA