It has been way too long since I've posted anything on this blog. Too many other things going on. However, a couple of weeks ago I made the mistake of trying to read the EEPROM on my ECU. I don't mean the large flash (29F200), but the little L56R (sometimes its a 93C56 - they are basically equivalent) next to the microcontroller. This little guy holds immobilizer related information.
Sadly, I wasn't successful, and worse yet, when I reinstalled the ECU, my car wouldn't start! I don't know if I damaged the ECU somehow, but my guess was that I had inadvertently modified the contents of the EEPROM and the immobilizer system wasn't happy about it. When I say "immobilizer system" I mean the ECU + immobilizer, as they work together.
So what to do? I figured that restoring the contents of the 93C56 was pretty much out of the question, since I had probably already scrambled it and I had no copy of the original data. Plus I'd have to desolder it to reprogram it anyway, which I didn't feel like doing.
My only other option was to try to figure out how to bypass the immobilizer. Long story short (and with the details intentionally omitted!), I was able to do this with just firmware mods (no hardware changes necessary, other than unplugging the immobilizer). Yup, I can now start my car with no immobilizer. Not the best solution security-wise, but it sure beats having to buy a new ECU/immobilizer/keys/etc.
Do you have an immobilizer issue? Here are some things you can try:
- If the ECU went bad and needs to be replaced, buy a used one of the same type, then swap out the little EEPROM with the one from the original ECU. Yes, you will have to desolder/solder a small surface mount IC. I highly recommend making a copy of the contents of this EEPROM while you're at it, just in case. From the immobilizer's point of view, the entire "identity" of the ECU resides in that EEPROM, so as far as it's concerned, after the chip swap, the replacement ECU will look just like the original one.
- If the ECU is good and the immobilizer needs to be replaced, this is a bit more involved. First, buy a used (known good) immobilizer. Make sure you can read the serial number on it. Then, you'll need a way of getting the code word from the serial number. There are programs out there that can do this. Most are not free, but I know of at least one where the "demo" mode will do this for free! It will be an 8 digit number. You'll have to program this into the EEPROM. I'm still looking for a way to do this without having to desolder the chip. There must be a way, because the manufacturer does it - but until I find it, you'll have to remove the chip and program it that way. If you are actually going to do this, let me know and I can help you out with the details. Once the EEPROM's copy of the code word is made to match the immobilizer, then the new immobilizer should work with the ECU. You'll have to reprogram your keys, too (you can find the procedure online). Caveat - I haven't tried this myself, so YMMV.
- If both ECU and immobilizer are replaced, and you don't have a matching set, do the same as if you replaced just the immobilizer, as I don't know how to change the code word in the immobilizer, or if it's even possible.
Anyway, I hope you never have a problem with your immobilizer system, and I'm glad my car came with one, but if you do, just know that there are cheaper ways to get up and running again than replacing the ECU/immobilizer/keys/locks.
