Passenger side headlight not working
I am in the same spot, hence this nudge to the top of this old post:
1. W220 S430, yr. 2000.
2. My lowbeam driver's side is out, but the bulb is fine (as is the replacement bulb that I installed). So, I presume a fuse issue. The fuse chart does not specify a fuse number.
3. Prior posts instruct: that the fuse for the head lights of the W220 is controlled by the "SAM Unit".
4. Forgive my ignorance, but what is the "SAM Unit"?
Any guidance is appreciated.
Ring A Ding
SAM is "Signal Acquisition Module." It functions as kind of a router, accepting signals from various controls and sensors, and routing the signals to the proper location to cause an action. A W220 has three of them - one under each front seat and one under the back seat.
The SAM unit does not "control" a fuse; but it would control the signals to operate a device on a fused circuit.
Regarding yours, if I were tinkering with my car and getting more failures than I started with, I'd realize I don't know what I am doing and take it to my dealer.
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SAM is "Signal Acquisition Module." It functions as kind of a router, accepting signals from various controls and sensors, and routing the signals to the proper location to cause an action. A W220 has three of them - one under each front seat and one under the back seat.
The SAM unit does not "control" a fuse; but it would control the signals to operate a device on a fused circuit.
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Last edited by Skylaw; Jun 4, 2019 at 08:44 AM.


If the headlamp does not burn, the usual list of possibilities include:
- The bulb has failed.
- The bulb is not installed properly.
- The bulb is not getting power. There is no "fuse" as such in the headlight circuit. The SAM (Signal Acquisition Module) on the opposite side monitors current flow to the low beam, and cuts off the power if the draw is greater than specified.
- The bulb ground connection is faulty.
- The bulb connector is not fully inserted. This should be the first suspicion of all of the lights in that headlamp housing have failed.
- The SAM or a connection has failed. This should be the very last possibility that you consider. Throwing parts at the problem hoping that something good happens is very expensive.
No magic answer - you are the only one who can test each of the possibilities and find the problem.



Now I can see where I'm going!!!!
