CoachWes

I just wanted to provide some information for those that run into the same problem as I did and I hope it helps point you in the right direction.

About 2 months ago at this point, I was getting ready to enter into the car wash and my car shut off and wouldn't crank back up. Long story short, it was towed back to my house and I started trouble shooting. At the time, I only had a Bluetooth scanner, and it was throwing out all types of codes that made no sense because they were not related to each other at all. If anyone really wants to know the codes let me know and I can go back and look at a few pictures. After tearing apart most of the wiring harness checking every single wire in the engine bay, it only left one possible cause, the ECU.

So I was at a cross roads because I'm about to give that car to my youngest son because he just got his permit and I want something safe and reliable for his first car. It has about 220,000 miles on it so its probably in the last quarter of its life anyway but I had made the decision to start repairing some things that I knew would be replaced if he was going to drive it such as shocks, control arms, etc. All of that is done and now this happens.

After doing some research, I found out that you can either clone them or you can have them repaired (sometimes). I first chose the repair route because it was going to be the least expensive and the quickest because I have a good PCB repair show here in town.

Well, as it turns out the capacitor had leaked and it didn't look that bad with the capacitor still on the board but the the repair show sent me some pictures after he removed it and it was clear that it had done some serious damage through all the layers of the board (see pictures). So the only option was to clone the board onto a used donor board. I got very lucky and found out that a guy that works at my company had access to everything that was needed to clone a Mercedes ECU. He doesn't do it but his buddy does. I had previously gotten into a conversation with him about my E350 and some work I was doing with the dreaded wiring falling apart, so that's how I knew that he may be able to help with the ECU.

As it turns out, it took longer than I had hoped for them to clone it but he also didn't charge me anything for it either. None the less, since it was gone for awhile and I had already taken most of the wiring harness off, I decided to go ahead and fix the other problem that we all face with the tumble flaps! I bought a repair kit, pulled the intake off and made the repairs. I finally got the ECU back and had already started plugging the wiring harness back together so it would be ready to just plug and play, so I thought! I plugged in the ECU and was excited to get my car going again but when I turned the key, nothing! ARE YOU KIDDING ME, what now? The key would turn to all positions but would not crank or start and all the lights worked on the dash. Well after some more trouble shooting and also investing in a Foxwell NT710 Scanner to get more accurate codes and the ability to make some changes if needed. The scanner however didn't throw any CAN codes but unfortunately, while I had all of the wiring harness disconnected, we had gotten several afternoon storms and water had gotten into the front SAM and also into the drivers side floor so I was pretty sure this is what was causing the issue.

If you didn't know, there are 2 CAN bus connections on the drivers side (and 2 on the passenger side) and the way the wire are run, the connections are at the bottom of the wire channel and are extremely susceptible to corrosion in the case there is any moisture in the floor. What had led me to looking into this was, there was the beginning signs of mold/mildew growing on the surface of the carpet. BTW, I live in SC so its been really hot this summer and it didn't take long for the mold/mildew to start showing up. Well lets just saw that troubleshooting CAN problems aren't the easiest when you don't have all the right equipment and only have a multimeter. I had removed both CAN blocks and cleaned them because there were signs of some corrosion on both but still, no start, no crank. I checked all the fuses and relays, took out the front SAM and cleaned any corrosion off of its boards, replaced with all new fuses (just happened to have a new kit with a ton of fuses). Still nothing!

The good thing about now having the Foxwell scanner, I could now get further into the system and get better live data and run tests on a wide variety of components. While working through all of the menus, I ran across Drive Authorization. Lucky me, I got to learn about the Mercedes DAS system. Everything for the most part was enabled, except for Start Enabled which seemed odd but I figured that it must not be getting an acceptable condition to allow start so back to the drawing board again. I printed out all of the wiring diagrams, taped together, and started testing every connection that I could until one afternoon, I got so frustrated that I couldn't stand it anymore. I came back and started to think, well, with the old ECU, it would crank but not start, so lets see if I can at least see if I can get this condition again to at least rule out any "new" problems that I may have caused by working with the wiring harness. Plugged in the old ECU and wouldn't you know it, it cranked but of course didn't start. So know I'm back to what's wrong with the new cloned ECU. Using my scanner, I went through each screen, taking a picture of each setting with the old ECU plugged in and then compared it to having the new cloned ECU plugged in.

To try and wrap up this story, ultimately it came down to one "minor" detail. When they cloned the ECU, I don't know if he was in a hurry or what but he did not change the VIN number to my VIN which in turn, didn't allow the car to start. The key fob matched the EIS so everything worked in the dash but because the VIN didn't match the VIN in the ECU, it would not enable the start condition!

Looking back, I'm glad I learned a lot of things along the way but wish it wouldn't have been so painful doing so.

So if you ever need any electrical drawings of a E350 with M272 engine, let me know because I probably have them!

Bottom the the ECU case

Bottom side of the ECU PCB

Capacitor that leaked/blew

PCB after capacitor removed

tjts1

Mounting the ECU on top of the hot vibrating engine was a daft idea.

CoachWes

I agree. I don't think that its is just by chance that this happened the same day that my car was running for awhile in the driveway while I was doing something in the car on a 100 degree day.

I've thought about how I can incorporate some type of fan, exhaust pulling air across or blowing fresh air across but I guess if I can get another 200,000 miles it will be OK but I'll probably be lucky to get 100,000 since the "new" one has already been used for who knows how long.

CaliBenzDriver

Thank you for sharing the many steps in your journey to fixing the original issue. Your soon should measure the effort you put in making this car great again.

I see your original ECU had what looks like a capacitor solder failure.
Based on that you could be dealing with a high ripples condition. Voltage ripples are what heat up the cap beyond already high engine bay temperatures....
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>> Evaluate how good are :
-- main single GND STRAP oxidized ?
-- voltage REGULATOR output??
-- main BATTERY charge level ?

The above items create unfavorable voltage ripples.