Hello, my m235i wouldn't start so i took it in and they say i need a new ECU and a ISM. They are quoting me $4400. I have done car work in the past and feel comfortable doing this type of work but I haven't reprogrammed my BMW before so I was wondering if this is something I could attempt or is it better to just let them do it? Looks like the ECU costs around 2k and the ISM is about $200 so labor is going to be about half of this cost. I've seen a couple youtubes on this topic and it doesn't look that bad but I was hoping to get better info from someone with more experience. I don't mind paying the cost if the quote is accurate and the job is out of my league but in these situations i really like to do them myself especially if it means I can buy the tools i need for the job and I still save money compared to what I would have paid the mechanic. Thanks a bunch, rick

Morning Rick

Welcome to the Forum

Well some one has to pay for the free coffee 😅

At the bottom of this issue is the fact that BMW do not repair anything? They replace components at their client/customers expense (they are not alone in this approach). If examined your ECU will have a corroded pin or a dry joint or two due to the failure they also want to change any component that communicates through the ECU like your ISM.

Early cars used to suffer FCM (footwell control module) failures BMW's answer New FCM and it can only be done by BMW as it has to be programmed to the car/chassis. There is no "programming" as such it is registering the module to the chassis to avoid getting a "tamper dot" beside the mileage figure.

As you have already seen it isn't that hard to do if you have the right tools. First source a matching set of ECU and ISM (used to be ECU and EWS) from a BMW Dismantler use www.realoem.com to get the correct part numbers for your model. Also buy a copy of BMW ISTA/INPA (preferred)  diagnostic suit or a good BMW capable diagnostic that will allow program/registration changes. With ISTA/INPA (the one I use) you can interrogate individual modules so first make a note of any information you can take from your existing ECU/ISM modules Serial numbers/chassis/ Vin numbers and mileage, BMW store mileage in 2 or 3 places/modules and they need to match (anti theft) Then it is a case of fitting the replacement parts and editing the Chassis information and mileage. Remember BMW do not make these parts they buy them in and rely on the fact that the vast majority of customers are frightened to even lift the Bonnet (oops Hood) educated to only respond to instructions on the cars screen 🤣

Once you have the diagnostics there is so much more you can learn about your car ISTA is complete with TIS (technical information system) and WIS (Workshop information system) 

Good Luck

Dave