97 s420 replacing w/ used ecu
 

Hey guys,

I have a 97 s420 and I was having problems with the fuel tank light which kept flashing at strange times when the tank wasnt empty and the ecu was throwing a code about evaporative system leak or something like that. After trying to repair many suspected problems I gave up and took the car to the dealer. They said my ecu was bad and needed to be replaced. I bought a used ecu and the car wont start. The dealership said the ecu has to be new. Is this true? and If I take the ecu to them will they be able to flash it or something like that? Or is there anyway for me to get it to work by myself. Thanks for the help.

Hikmat

You will need to be a first class hacker to use a used control unit. The control unit marries the chassis number on the 40th key cycle once in use. This can be reset indefinitely untill it goes once to 40, then its married forever.

Some of the rebuilders can clear the coding but it is not a factor handled with factory tooling. The dealer can't do it.

I bought a bunch of controllers on ebay for a song due to this and traded them to a rebuider to rebuild (unlock) one for me. I keep it as a test tool. Fits an amazing number of cars. The rebuilder I use is http://www.beckmanntechnologies.com/

Hey thanks for that info it helps. If I was to buy a new ecu I wouldnt need to take it to a dealer right for any type of flashing? Its plug-n-play right?

Also I was wondering if you knew any shops that would clear the coding? I found some like ecudirect.com but they wanted around 500 for rebuild of my malfunctioning ecu. Any shops or places you know that I can send it? Thanks

Hi,
As far as i know here in UK the ecu is programmed in Germany and then sent to dealer. As said above the ecu has a code which links to the other components and if they do not match then nothing works.
I was looking to but a used gearbox ecu for £190 ukl as new from dealer in £490 ukl, but after speaking to a few MB technichians who i know they all advised against it and told me that the codes cause too much hassel and is easier to buy of dealer pre programmed to you chassis number and car.

Regards

You probably checked this out already, but let me mention it anyway. I was at a service station getting gas with my son. It looked like rain, so while I was putting Rain-X on the windshield he finished fueling the car. A ways down the road the fuel guage started flashing and the CEL came on. The code was something like "evaporative system leak-gross". It turned out that my son forgot to put the fuel cap back on! I bought a new cap, cleared the fault, and it's been fine since. I doubt you forgot to put the cap back on, but maybe it's loose or has a leak.

I tried changing the cap to an oem one. As well as the sensor for the fuel tank and the gauge cluster. All no help. Dealer diagnosed it as a faulty ecu. Ill double check the gas tank though.