Mercedes ECU Exchange
A new challenge came my way this week. A shop was working on a 1996 Mercedes and decided it needed a replacement ECU. They purchased a used one off the internet. The immobilizer was enabled due to the swapped ECU. The goal was to get the vehicle to run. After getting on site I realized that this would be a challenge. My cloning tools did not have the capability for a ECU this old. Searches on the internet yielded dissimilar ECUs and some scary methods.
I had my soldering and rework gear with me so I decided to exchange the most likely parts in order to get the vehicle to run. I first changed what appeared to be the EEPROM on the lower side of the board. I then installed the ECU and tried to start. No fire. I then exchanged what I was pretty sure was the calibration memory. No Start. Then another memory chip. No start. I had to go to another couple of appointments so I told the owner I would need to work on it overnight.
When I got to my home office I again browsed the internet for any hint of where the immobilizer info was stored. I also consulted with another expert well known on this forum. All the chips were re-branded so it was difficult to determine what could be the one. Between browsing sessions I decided to try and read the EEPROM off the under side of the board. I was able to read the VIN in the EEPROM which matched the original ECU.
Another session online and I found an Easter Egg. In one of the forums a guy was wanting to do an ECU swap with a very similar ECU. It seems in the forums many of the ones in the know will give you just enough information to get you hooked. One seasoned sage suggested that the immobilizer data was stored in the HC11 chip. From further comments in the forum, I was able to gather the HC11 was re-branded as a 30196. I then removed this chip from the original ECU and installed in the donor. Once installed the vehicle fired right up. Success!
I have labeled the chips as I understand them on the board. Not to be taken as absolute......
Great work Michael!. What tool are you using to read the EEPROM?
Hi Carl, I am using the Andromeda Research AR32A. It is a little dated in the way it works but it can read and do some pretty cool stuff. I also often use the VVDI Prog tool. It is easily sourced in Europe. arlabs.com
Thanks for that Michael, I will look up those tools. It's an area which interests me greatly but I am very green.
Michael should a Benz situation like this arise in the future please reach out to me. You do so much here on DN and I want to return the favor. 1996 HFM control units are really goofy. It was the first year where the PCM was closely tied to the immobilizer system. Older cars at Best had a starter lockout relay. Many scan tools claim to be able to "program" them but only if they arrive to you in…
Thanks Robert, All the numbers on the outside matched and the ones on the inside matched. I guess I got lucky. Changing the one I assumed was the HC11 did the trick. I will surely reach out next time I get one of these. -Mike
One more thing. Some of the HFM units have the eeprom on topside of the board!
Michael- What are these forums you speak of? Links?(are they the wild west forums someone listed earlier?)
Hi Rusty, I usually just start Googling different terms to get to the forums. Mercedes ECU, EEPROM, Mercedes Immobilizer and so forth. Keep in mind it is not likely anyone will post everything you need. Typically they give you a little information and you then have to connect the dots. It is like a big puzzle with a prize at the end.
Nice work Michael ... it’s great to have these documented for a possible next case situation or simply to archive the device markings for reference on possibly another different year make or module
Great Work and very interesting Michael !
Thank you very much Michael! This is an area of great interest to me. I have been looking at VVDI tools, and trying to find eeprom readers/writers to do what you did here. I have a video saved in my iATN archives where someone did the same thing to a Global A pcm on 2010 GM. They were able to erase the vin in the used pcm, write the correct vin in, and the pcm allowed the vehicle to run. Thank…
HI Paul, VVDI Prog is a great tool. You can also use the Auto Pro Pad for many EEPROMs. As mentioned above, I really like the AR32A. It has an old school DOS look but reads a huge variety of chips with the proper adapter. We are looking at a less expensive EEPROM tool that looks promising as well. In addition you need to be able to safely exchange chips. A good pair of jewelers magnifiers and…
Michael, Without a doubt a new frontier. I have been dabbling over the last couple of years with EEPROM work. I have received some great advice from many. Like anything in automotive is you have to put the time and research in. Also, practice and more practice. I thought I was pretty good with soldering. Boy, did I need to improve my skills. I look at it as an extension to my mobile…
Hi John, These processes are a huge time burner. I end up spending many late nights not able to sleep due to not figuring something out. Once a module is figured out, the second of that type goes more smoothly. That is when you start to see profit. When you can knock something out in an hour instead of six. Soldering is an art. I feel my age every time I have to do board level work. You start…
This is something I am very interested in. I have recently chatted with a few of my peers about learning board repair. I don't come across failed module too often. When I do, they are not the easiest to source. I would be very interested in training on the topic.
Hi Blake, We are looking at doing online training and then doing in person classes. On board repairs will be covered in one of the classes.
Great write up, Thanks for the info and your time and thoughtfulness in sharing.