Right Headlight

Kyle Diagnostician Philadelphia, Pennsylvania Posted   Latest  
Discussion
Electrical
2008 Mercedes-Benz C350 Sport 3.5L 7-spd — WDDGF56X18F053030
Right Low Beam Headlamp Inoperative

This vehicle was in the process of being inspected when the passenger low beam stopped working. The tech at the shop tried a new bulb w/igniter. He also removed both headlamp assemblies and swapped their positions (obviously just plugging in the electrical connector), both assemblies worked as expected in the driver side. Neither low beam worked on the passenger side.

I was asked to look at the vehicle. Using my Verus Edge I was able to command all of the lights on except the passenger low beam. Each light appears to be controlled individually by a lighting module bolted to the bottom of the headlight assembly. 

Both headlight modules have two CAN lines (based on the schematic one high & one low) that come from the signal acquisition module (SAM). At this point I scoped both sets of lines coming into the headlamp assemblies.

This is the baseline capture with no light activation:

diag​.​net/file/f44n5fnzt…

This is the left/driver low beam activation:

diag​.​net/file/f60j070q1…

This is the right/passenger low beam activation:

diag​.​net/file/f3bk69bqt…

At this point it looks to me like the SAM isn't commanding the passenger light on or if it is it's very brief. Unfortunately these were the best captures I could get using the Verus. I have included the original scope files as well if anyone wants to take a look at them. 

If I'm being honest I'm not very familiar with this set up for the exterior lights and I am basically hoping a fellow tech might be able to tell me if I'm missing something.

+2
Interesting
Thanks
Jim Owner/Technician
Charlotte, North Carolina
Jim Default
 

Kyle, I believe the headlamp module will try and turn on the lamp- but if it doesn't light then it stops trying to activate it. BMW has a similar strategy,

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Kyle Diagnostician
Philadelphia, Pennsylvania
Kyle Default
   

Hey Jim, Thanks for the input. What do you think about the fact that both lights (the complete assemblies) can be put on the driver side and function? I forgot to include that I'm scoping all four lines as follows: Yellow=Left Headlight Can-G H Green=Left Headlight Can-G L Blue=Right Headlight Can-G H (inverted) Red=Right Headlight Can-G L (Inverted) I had to invert the second set to get…

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JJ Technician
Quincy, Massachusetts
JJ Default
   

Have you checked for voltage drop at the right headlight's ground wires? No ground, no light, module cuts power. In the interest of transparency, I don't work on any Euro makes, but voltage drop comes to mind. I'm thinking check for a quick pulse of voltage at what appears to be pins 5 and 10 of the right headlight unit, brown wires. Edit: Pin 5 looks to be the high beam ground, maybe disregard…

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Kyle Diagnostician
Philadelphia, Pennsylvania
Kyle Default
 

Have you checked for voltage drop at the right headlight's ground wires? No ground, no light, module cuts power. In the interest of transparency, I don't work on any Euro makes, but voltage drop comes to mind. I'm thinking check for a quick pulse of voltage at what appears to be pins 5 and 10 of the right headlight unit, brown wires. No admittedly, I didn't. I did static/unloaded tests for…

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Jim Owner/Technician
Charlotte, North Carolina
Jim Default
 

Looking at the diagram, it looks like the headlights have different controllers. Are the controllers being swapped as well? Can you clear faults from the module(s) and see if the drivers side will work on the pass side- I've had several MB lighting issues that wouldn't work properly until I cleared the faults. Also - can you scope the power feeds from the SAM module to the headlights? It looks…

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Kyle Diagnostician
Philadelphia, Pennsylvania
Kyle Default
   

Hey Jim, Looking at the diagram, it looks like the headlights have different controllers. Are the controllers being swapped as well? The entire headlight assemblies (each assy has it's own controller bolted on the bottom) have been swapped from side to side with all lights working on the driver side in either light assembly. Can you clear faults from the module(s) and see if the drivers side…

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Sisco Owner/Technician
Mendon, Vermont
Sisco Default
 

Codes?

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Kyle Diagnostician
Philadelphia, Pennsylvania
Kyle Default
 

Codes? No codes and if memory serves no communication with the right headlamp module either. ~Kyle W.~ ~The Texadelphian~

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Jim Owner/Technician
Charlotte, North Carolina
Jim Default
 

I don't think you're missing anything, and based on what you have done so far, and provided that power and grounds are a non issue, I'd say you are on the right path with replacing the SAM module,

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Stephen Technician
Gallatin, Tennessee
Stephen Default
 

Since the right assy works in the left socket, I would think the assy is OK. With the one wonder, are the lights programmed to function only as a left or only as a right side? Are they able to be turned on/off individually? The same CAN bus feeds both sides and the captures show that the CAN lines are equal. Since one side works that would rule out the CAN bus. But the CAN would need to be…

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Carl Technician
Baytown, Texas
Carl Default
 

Does this vehicle have intelligent lane ? I was reading all the different options that were available and how they could effect the Sam... It has two processors that communicate with each other, and the lights are powered separately . I cant think of any reason why it was tell the light to wink unless it has the hot chick option. Good news that means its probably no power, no ground or bad module.

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