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EPROM for Automotive

Discussion in 'Microcontrollers, Programming and IoT' started by Rosco, Nov 17, 2016.

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  1. Rosco

    Rosco

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    Nov 17, 2016
    Hi, I'm an automotive technician, and was called to a shop to program a car's vin into a new ECM. After arriving, I learned that it was a used pcm, and this particular year didn't allow you to reprogram. So, I removed the EPROM from the original ecm (with the car's vin already programmed into it) and soldered it into the replacement pcm.

    Unfortunately, the problem was the EPROM itself. This rarely happens, but there was actually a code in the computer saying that it was bad - in not so many words. It was as code P0605 - ROM error. Since there were other IC's with memory and I was out of options, I swapped them.

    In this particular case they could have ordered a remanufactured pcm for less than they paid for the one from the junk yard.
    That isn't always the case though. Sometimes they're $2000. Plus labor and the cost of programming on a $3000 car. It's not happening.

    This brings me to my questions.

    Would this EPROM, which contains the software that runs the car and the immobilizer information, have a BIOS in it, or would the BIOS be in another IC?

    If it does contain a BIOS, would it be programmed in from the IC factory or would it be a part of the program that I install when flashing a new computer into the car?

    If the BIOS is in the EPROM and already in it from the original factory, is it erasable?

    This last question I'm wondering because the code refers specifically to a ROM error. I'm wondering if there is a non erasable portion of the EPROM.

    The reason for all of these questions is to figure out if I can just buy a new EPROM, put it in, and program it. (or an erased EPROM)

    Thanks
     
  2. Rosco

    Rosco

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    Nov 17, 2016
    It is definitely an EPROM. I looked up the data sheet on it. It is obd2. Some cars use EPROM instead of EEPROM so that yu can't put a used computer in. Not very many techs have a uv eraser.

    I did replace the EPROM. The problem was that the EPROM with the correct vin programmed in it had a ROM error.

    I'm looking for answers specifically to the questions that I asked.
     
  3. davenn

    davenn Moderator

    13,866
    1,958
    Sep 5, 2009
    quite possibly

    the BIOS most likely, but not necessarily would be in the CPU IC

    not if it is a standard EPROM
    but since you have told us nothing about the specifics of the EPROM, it's anyone's guess


    Dave
     
  4. Rosco

    Rosco

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    Nov 17, 2016
    IMG_20161116_123039195.jpg
     
  5. Rosco

    Rosco

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    Nov 17, 2016
    I was looking for an answer that would apply to most ECM's. Which is why I didn't think to give specific info. I service all makes and models, so I need general info. Such as what you gave. It sounds like, from what you're saying, that I could most likely buy a new EPROM and program it.
    Thanks.
     
  6. davenn

    davenn Moderator

    13,866
    1,958
    Sep 5, 2009
    That isn't an EPROM

    it is a PROM

    http://www.datasheetarchive.com/AM29F400B-datasheet.html



    Dave
     
  7. Rosco

    Rosco

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    Nov 17, 2016
    Thanks. That explains why I didn't see a quarts on it. I must have read the data sheet wrong.
    Aside from it not being erasable, does that chang anything? Bios is most likely in the processor? If in the prom would be installed with the program?
     
  8. davenn

    davenn Moderator

    13,866
    1,958
    Sep 5, 2009

    That's unknown, only the manufacturer could answer that
    It may or may not be written into the PROM
     
  9. Rosco

    Rosco

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    Nov 17, 2016
    So it is possible to write bios into a prom, put it into the ECM, sell it to the tech, whom then flashes the program into it?
     
  10. davenn

    davenn Moderator

    13,866
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    Sep 5, 2009
    Like I said, only the manufacturer could answer that :)
     
  11. Rosco

    Rosco

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    Nov 17, 2016
    I'm not asking if they do. I just need to know is it possible to write bios onto a prom and then write a program onto it. My understanding of a prom is that you can write onto it once and never again. If that's true then there couldn't be a bios on it before the program. I put the program on it, so that would mean that I could buy a new prom and flash it myself.
    This all assumes that it's not possible to write a bios onto it then the program at a later date. Based on the principle operation of any prom not any specific one.
     
  12. tedstruk

    tedstruk

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    Jan 7, 2012
    thats a 42 pin SMD and it looks like a prom when I look at that data sheet.
    you need it reprogrammed or you should consider replacing the entire unit.
     
  13. Rosco

    Rosco

    9
    0
    Nov 17, 2016
    Yes. I do the reprogramming. In this case the customer should have purchased a new unit as they're cheap. Sometimes they're really expensive though. I'm trying to determine if I can put a new/blank prom in it and flash the vin on it. I presume that this is what the remanufacturers do. (Put a new prom in it and clean it.) Then the tech flashes it.
     
  14. davenn

    davenn Moderator

    13,866
    1,958
    Sep 5, 2009
    they could be written sequentially to two different parts of the ROM

    AGAIN, the MANUFACTURER ... IF he is willing to share info, would tell you what they have done
     
  15. Rosco

    Rosco

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    Nov 17, 2016
    Okay, so it is possible. A solid no would have meant that it was possible to do what I wanted to do for sure. Your answer tells me that it's not likely.
    Working on automotive modules is like working on mac products. No info will be provided and as of late, is sealed so tightly that you risk breaking the circuit board removing it from the case.

    Thank you for your patients and persistence with helping me.
     
  16. tedstruk

    tedstruk

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    7
    Jan 7, 2012
    SMD wow. It didn't even exist when I was a kid.
     
  17. NMNeil

    NMNeil

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    10
    Oct 3, 2014
    What make model and year?
    The reason I ask is that all ECM's can be flashed. Never ever heard of one that was 'locked'
     
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