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

After the technician found no diagnostic trouble codes and verified that there was no battery power to the passenger low and high beam headlights, he called ALLDATA Tech-Assist for advice.
June 5, 2020
2 min read
Alldata Black 56dde4a32926a 5ed956a06d4f5 5eda6ea95cd50

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

Sign up for FleetMaintenance eNewsletters
ID 258136336 © VanderWolfImages | Dreamstime.com
dreamstime_xxl_258136336
To help rein in the costs of fleet electrification, fleets should consider how they’ll manage their energy costs after their EV infrastructure is in place.
Ford
Ford F-150 Lightning construction
Here’s how fleets are using electric pickup trucks in their operations today, and why they’re not going back to gas- or diesel-powered engines anytime soon.
ChargePoint
chpt_eaton_1
As part of their partnership, ChargePoint and Eaton will work to provide EV chargers, electrical infrastructure, and engineering services for transportation companies.