Car: E320 CDI

Year: 2005

Problem: Car won't start

I'm a long-time owner of a 2005 E320 CDI. (CDI = Diesel version)

Recently the car failed to start. Insert key. No sounds, no clicking. Nothing. Almost like the battery was disconnected. But the windows would go up and down, the trunk would open, etc. So obviously there's power somewhere.

I had the car moved by roll-back wrecker 94 miles to the independent shop that has repaired it through the years. They got it to start and I drove it home. It operated normally for a few days, but the same no-start problem returned. Once again, on the roll-back wrecker to the shop for a second time. They get the car to start. I go to pick up the car, and when I'm ready to leave the shop parking lot, the car will not start.

(For background information, the shop owner was a top tier technician, working for 20+ years at a Mercedes dealership. When he retired from the dealership, he opened his own independent M-B repair business. A legitimate 7 a.m. until 5 p.m. brick and mortar business. He's NOT someone working out of a backyard shed. His shop has Star diagnostic technology.)

Now back to the problem: When the car refused to start in the parking lot, he raised the hood, opened the fuse box next to the firewall, and tapped around with his pocket knife. He said he thinks the trouble is in the SAM, the “signal activation module.” So after making a couple of “taps,” he told me to “try it,” and the car started. Yippee! But a few days after I got back home, the car again failed to start. I repeat his “tapping” process, and after a couple of tries, the car started.

Once the car starts, it drives just like normal. After tapping it to start, I drove the car on errands and, you guessed it, I leave a store and the car won't start. I slid off the fuse box cover and tap and the car eventually started. Naturally, this is very frustrating.

After talking with the repair shop owner via telephone, he suggested I take the car to the Mercedes dealer in my city and have them look at the problem.

(Just for additional background, I've paid $600-plus to get the car towed twice to his shop. Towing to local M-B dealer is $60. He said he was trying to save me some towing money.)

Now, back to the problem: He says to tell my local M-B service adviser for the dealership to zero in on the SAM area. My out-of-town tech said to tell them he would be glad to talk with their adviser and share his diagnostic information with them.

What he thinks is water has gotten under the slide-off cover where the SAM is located and has caused corrosion to form. When he started his diagnostics, he said the cover was not properly latched shut. (It is situated just below the area where the wipers push the windshield rain.) He thinks it likely has corrosion inside. He believes this because my SAM unit tests “good,” but he admits the problem is occasional, AND that the tapping MIGHT jiggle the electrical connections just enough to make better contact, therefore the car starts.

My man doesn't trade out parts or install used parts. He only installs “new,” and says if he installs a new SAM, it would cost more than the car is worth.

So with all this information I've provided, here are my questions:

Situation A:

1.) Can my SAM unit be unplugged and “opened” so the corrosion can be gently cleaned away by using a baby toothbrush and spray-on electronic contact cleaner?

2.) If I do this cleaning, will the car have to be re-programmed after the SAM has been removed, cleaned and re-installed?

Situation B:

1.) Can a used SAM that tests “good” and has no corrosion be purchased on eBay be traded out with my unit? I understand the used replacement needs to be from my exact car, meaning a matching part number from an identical 2005 E320 with CDI?

2.) If it can be traded out with an exact, identical replacement, will the car have to be re-programmed in order for all the functions throughout car to work properly?

The last thing I want to have happen is kill the car because of my ignorance of the SAM unit.

I've probably already spent more money on the towing and diagnostics and other services than the car may truly be worth. The car looks good on the outside, it's 100% rust-free, has a 99% perfect interior, nearly new tires, and until now, has been totally reliable. It has had great maintenance, including documented oil changes, transmission fluid changes, brake fluid and coolant changes, etc. It has 220,000 miles on it, but after all, it is 17 years old. It easily gets 37 miles per gallon driving at 75 mph to 80 mph on the interstate.)

Can anyone with genuine knowledge give me advice regarding the SAM unit and the need for re-programming. I'm not one bit afraid to handle the “remove, clean and replace” work. It is the re-programming I know nothing about and am fearful of doing without professional advice. Will removing the SAM, cleaning the corrosion and re-installing it keep the car from starting?

My humble appreciation to all who have read, and particularly to anyone who can give me real-world advice on the need for re-programming.

Thanks, and best wishes,

– Ed Rouze

 

No, you don't need reprogramming if you take out the front SAM and clean it, same goes if you get used unit with same part number.
Front SAM is also easy to take apart, unlike the rear which is pain and requires solder gun to remove contacts from the board. But on front you just remove few screws (T10 head IIRC), and pry tabs that keep the cover on.
​​​​​​And when you have the module out, check all the electrical plugs that they are clean. Especially if the corresponding connector on the module side has corrosion.

 

With chip shortages & supply chain issues worsening worldwide, we are relegated to DIY junkyard swapping to keep our precious CDIs from becoming salvage for parts. Here is one accidental success story for encouragement & inspiration: I hope you're able to get it reliable again w/ a sam swap. Good luck! Stealership will likely NOT be helpful (they are part of a green new deal agenda) as their goal is to stick you in one of their new electric vehicles if they even have anymore to sell. Same supply chain disruptions are affecting inventory of new vehicles apparently as well,

 

Check starter relay fuse f59 (15A) & relay L including connection points. Fine, pull SAM to visually check all connectors/pins.

 

If your SAM got swamped, there's a strong 80% chance you're better off getting a clean spare replacement.

Have a look anyhow at your original unit to see if indeed it shows water damage. Perhaps only the relay got swamped... sometimes luck has its own ways to work.

These old SAMS do not require programming as stated by YT "Car D Ologist" himself. These parts are unexpensive to have laying around.

Be proactive, go research the sources of "water intrusion", free time well spent !

Feel free to post good picture of your unit, I might be able to point out a few things... such as simple solderless pins?

👍

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