'09 R320 Bluetec- no tail/brake loghts after installing repair harness - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 07-30-2019, 10:15 PM

I installed the two repair harnesses (164-826-00-07) on an '09 R320 Bluetec, and there is still the tail/brake light warning on the instrument cluster. I checked for power on the wire, and there is none. I also used my Icarsoft MB II and monitored the live data. It says there is an open or short in the wiring for both bulbs. When stepping on the brake, the monitor shows both lights being off. I am not sure what to do now. Anyone have experience with this issue? It happens on the ML and others as well. Thanks, Rich

EDBSO · #2 07-31-2019, 12:38 AM

Not confident in this answer BUT when I lost the rear lights on my 2006CDI it was the rear SAM that was defective $$$$

Diagnosed and replaced by dealer.

Father Of Giants · #3 07-31-2019, 06:15 AM

This sounds most likely like a communication issue, because both are out at the same time.

Or simply a bad brake light switch?

Or bad brake light assembly contacts? Read Dspicher's post, very interesting.
https://forums.edmunds.com/discussion/5796/mercedes-benz/r-class/mercedes-benz-r-class-electrical-problems

Does the IcarSoft MB really say "Open or Short" if so.

If it where a true open you'd have 12v at the beginning of the brake light circuit, but 0v at the bulb.

If where a true full short to ground it would read 0v at the source (where the circuit begins) and 0v at the load.

That's all I can think of.

ROLLGUY · #4 07-31-2019, 01:23 PM

Quote:

Originally Posted by Father Of Giants

This sounds most likely like a communication issue, because both are out at the same time.

Or simply a bad brake light switch?

Or bad brake light assembly contacts? Read Dspicher's post, very interesting.
https://forums.edmunds.com/discussion/5796/mercedes-benz/r-class/mercedes-benz-r-class-electrical-problems

Does the IcarSoft MB really say "Open or Short" if so.

If it where a true open you'd have 12v at the beginning of the brake light circuit, but 0v at the bulb.

If where a true full short to ground it would read 0v at the source (where the circuit begins) and 0v at the load.

That's all I can think of.

I thought about the brake light switch being the problem, but since the tail light and brake light are the same bulb, the tail light would/should work even if the brake doesn't. These single filament bulbs are connected to a module that puts a lower voltage for the tail light, and higher voltage for the brake. I believe all MB's since 2003 are like this. I fear it may have a bad SAM as EDBSO described. If there is a separate module for the rear lights, it may be easier/cheaper to fix. However, if the rear light control is in the rear SAM, then it could get expensive. These cars have separate modules for each door, the overhead, and tailgate. I need to do more research and find out if the lights are controlled by a module, or the SAM.......Rich

jay_bob · #5 07-31-2019, 04:21 PM

Tail lights on the modern MBs are on the rear SAM. They use a single filament (or LEDs for the really new ones). Our favorite friend PWM (pulse width modulation) is at play again here. Applied voltage is always 12 V, but it gets switched on and off rapidly to make the light appear dim for marker light mode. Brake mode gets constant 12 V dc.

If you’re having trouble and you’re sure it’s not the wiring or the socket it will be the SAM. They use a power semiconductor to switch the voltage to perform the PWM. I suspect that this is a readily available MOSFET that can be replaced easily.

ROLLGUY · #6 07-31-2019, 11:29 PM

Quote:

Originally Posted by jay_bob

Tail lights on the modern MBs are on the rear SAM. They use a single filament (or LEDs for the really new ones). Our favorite friend PWM (pulse width modulation) is at play again here. Applied voltage is always 12 V, but it gets switched on and off rapidly to make the light appear dim for marker light mode. Brake mode gets constant 12 V dc.

If you’re having trouble and you’re sure it’s not the wiring or the socket it will be the SAM. They use a power semiconductor to switch the voltage to perform the PWM. I suspect that this is a readily available MOSFET that can be replaced easily.

I checked it today, and I was mistaken about the center brake light. Id does in fact work, so I imagine the brake switch is good. What is this MOSFET you speak of? Is there a place that can repair something like this?

jay_bob · #7 08-01-2019, 12:12 AM

MOSFET is an acronym for a Metal Oxide Semiconductor Field Effect Transistor

It is a highly efficient device that switches dc voltage on and off with a small dc triggering signal. Thus making it perfect for switching the several amps of dc needed to light several tail light bulbs with only a few thousandths of an amp from a logic chip.

Never had a SIM apart before but if you pop the top off you will probably see some devices that have a black case, bolted to a heat sink, about the size of your thumb nail. With a little sleuthing (look at the board traces) you should be able to find the one that has a connection with the tail light pin on the body harness connector. Then with a meter you should be able to probe the pins on the device and find one that has 12 V (the ‘source’), one going to the bulb (the ‘drain’) and one that is leading from the logic chip on the SAM (the ‘gate’). When the gate is energized it allows current to flow from source to drain and out to the load (light bulbs).

Look at the markings on the front of the device and punch into Google. May have to search for ‘semiconductor trademark images’ to get the manufacturer’s name. Once you’ve figured this out you should be able to go to Digikey or Mouser and order a new one. They have minimum orders so you’ll probably have to order multiple to meet minimum.

Then it’s just a matter of being handy with a soldering iron and swapping the component.

ROLLGUY · #8 08-01-2019, 12:32 AM

Quote:

Originally Posted by jay_bob

MOSFET is an acronym for a Metal Oxide Semiconductor Field Effect Transistor

It is a highly efficient device that switches dc voltage on and off with a small dc triggering signal. Thus making it perfect for switching the several amps of dc needed to light several tail light bulbs with only a few thousandths of an amp from a logic chip.

Never had a SIM apart before but if you pop the top off you will probably see some devices that have a black case, bolted to a heat sink, about the size of your thumb nail. With a little sleuthing (look at the board traces) you should be able to find the one that has a connection with the tail light pin on the body harness connector. Then with a meter you should be able to probe the pins on the device and find one that has 12 V (the ‘source’), one going to the bulb (the ‘drain’) and one that is leading from the logic chip on the SAM (the ‘gate’). When the gate is energized it allows current to flow from source to drain and out to the load (light bulbs).

Look at the markings on the front of the device and punch into Google. May have to search for ‘semiconductor trademark images’ to get the manufacturer’s name. Once you’ve figured this out you should be able to go to Digikey or Mouser and order a new one. They have minimum orders so you’ll probably have to order multiple to meet minimum.

Then it’s just a matter of being handy with a soldering iron and swapping the component.

Wow, that all sounds like fun. A little scary, but it may be fun. I am not that good with electronics, so I may enlist the help of an expert. Where would I find a pinout diagram for the SAM? That would make it easier to find the right component, should I take on this task. Thanks, Rich

jay_bob · #9 08-01-2019, 12:40 AM

If you have a Xentry computer there is a wiring diagram tool called Star Finder.

Otherwise there is Mitchell or Alldata on the internet.

ROLLGUY · #10 08-01-2019, 10:58 AM

Quote:

Originally Posted by jay_bob

If you have a Xentry computer there is a wiring diagram tool called Star Finder.

Otherwise there is Mitchell or Alldata on the internet.

Having several, and servicing 2003 and newer MB's, I should probably have an Xentry. If I could find a good deal on one, I would buy it. For now, Alldata will have to be what I will look at. My A/C shop buddy has it and I can probably have him look it up and print it for me.