pstutcher

I just picked up a bargain buy of a 2004 E320 4Matic Wagon. It runs and drives great but there's lots of issues I'm working thru 1 by 1. I'm stumped by one that's keeping me from putting it on the road: No brake or tail lamps.


Here's what's up:


No brake lights, EXCEPT the center high mount light, which does work.

No tail lights

No rear turn signals

No tail gate interior light


There's a number of things at the rear that do work: center high brake light as stated, rear fog light, license plate light, reverse lights, rear wiper, rear latch electric release and closure motor, rear defrost.


OBD shows tail gate control module (signal acquisition module, or SAM) is not reporting on CAN. It specifies the N111 SAM located in the tail gate, not the main rear SAM with the fuse box in the left side rear cargo area.


There's +12V at the tail gate SAM on both the standby and accessory 2 power wires.


All grounds at the tail gate SAM are good


All grounds at every bulb connector are good


All bulbs light when connected directly to 12V


The electrical mechanisms for the rear tail gate latch work, both to release the latch and pull it to final closed position. I mention this because power for these passes thru the tail gate SAM.


Given all of this, I concluded that the tail gate SAM had gone bad. It's getting power and is properly grounded but isn't reporting to CAN or turning on any lights it's supposed to .


So i find a salvage part online and plug it in hoping it solves the problem. It does not. Symptoms are identical, so it's not the tail gate SAM.

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I took the covers off the SAM thinking I might see corrosion or burn marks on the circuit board. I found nothing that looked off


So next I stripped out the rear SAM from the cargo area thinking I might find corrosion or burns. Nothing


I'm lost as to what to do next except the dealer, which I'm loathe to do because my experience with my local dealer is that they very much pursue a mentality of 'let's start changing stuff and see if it helps' and it has cost me a whole lot of unnecessary expense on my CDI.


There is one other conspicuous error showing on the OBD. It's error code 930E and states 'signification synchronization of the DTC memory cannot be ensured'. I have no idea what this is about.


I'm stumped on what to pursue next. Please help.


Pete

pstutcher

I forgot to add a few things:

All fuses on the vehicle are good, although the one for NAV was blown when I first got the car.
All relays appear to be working
I replaced the main battery in the rear with new, the old one was dead
The aux battery is good
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I've searched this and other forums plus the Internet at large and I'm not seeing anyone describing a situation that matches this.

Again, please help, I'm stuck on what to go after next.

CaliBenzDriver

These lights have got to work!
You did a comprehensive survey of the chassis with very little improvements.


Your preliminary work gives you confidence of what's what and everything that's good.
There's something derailing your party that we need to discover....

I think this issue is centered around Rear SAM not reacting.... like a bad CAN-B preventing orders from coming in.

We are not going to replace perfectly good parts without testing what we can.


Use your bi-directional scanner to trigger the Rear SAM light output of your choice.

Scan the whole chassis for evidence of what's at play mainly on CAN-B where R-SAM lives.

pstutcher

I don't have a bi directional scanner, so I might need an investment there. Oh, and learn what that is and how to use it.

Something I noticed today that puzzles me further. There are lights on the tail gate that run thru the tail gate SAM, but there are also lights on the body and as I was dismantling things today I noticed that they run straight to the rear SAM that's integral with the rear fuse box. The body lights don't work either. BUT, there's lots of other stuff going thru that SAM that works fine.

The conundrum is that the lift gate lights don't work but since it's not reporting on CAN, there are no warnings in the dash about the lights not working. Ok, that makes sense to me. But how are lights that failing lights that are on the other SAM, the SAM that works otherwise, that aren't being reported as not working?

CaliBenzDriver

The front SAM manages power to chassis modules plus front lights.

The rear SAM manages rear lights by communicating with front SAM over CAN-B.

CAN-B has the most modules connected to it... any swampy module can impact COMS for the entire bus.

Even with all the knowledge and schematics you can gather you won't know for sure what's wrong!

The chassis has endless ways to disfunction.
Any good scanner is not tell you what to do next... it's only a necessary troubleshooting tool.


You can disconnect all batteries and then cleanup GND posts around trunk area and Rear SAM.

pstutcher

Thanks for the response. By swampy do you mean that it's been wet?

If so, it seems to me that I should pull each SAM, open it up and look for corrosion or burn spots, right? It's just a matter of learning where they all are.

As for the grounds, I've torn apart a large portion of the cargo area checking for loose grounds, things disconnected, loose, wet, corroded, etc. Nothing so far.

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CaliBenzDriver

yeah... "swampy wet" when water meets electricals: in the trunk, in the front footwell and front SAM.

When you decide to remove modules... do remove battery power first!

SAM's are "smart fuse boxes" connected to CAN bus for control.


The sooner you can locate your bad electrical item, the sooner you can do something else... like regular engine maintenance.


> Homework study:
​​​​​​​learn about the "CAN Bus distribution bars" located near footwell and door seal. This will help you troubleshoot CAN-Bus with your good scanner.