Transponder synch to ignition key? - BMW Forum

kstesney · 10-02-2009, 12:09 PM

My 2003 BMW 325i has a rebuilt title. Since I bought it a couple years ago, it has generally been fine, with no evidence of ever being rebuilt, except a good mechanic had to do some rewiring to correct the outside temperature sensor. He said although I live in Florida, the car thought I was in Alaska. That's why my A/C kept failing when it rained and the windows got all foggy. Anyway, that's not a problem anymore. But here's the real kicker. I have always had only one key for this car and I have been worried that if I ever lose that key I'd be out of luck. So I went on Ebay and got a programmable replacement key. It turns out the replacement key could be programmed to lock and unlock doors and trunk, etc. However, it was a blank key and had to be cut. Car Max said they could do it, and did cut the key, but said they could not get it to start the car. They did not charge me anything (good guys). So I went to the BMW dealer and they could not program it either. Here's the kicker: they said that my key did not match the vehicle ID. Somehow, in the past someone had changed the key and related communication with the engine from another vehicle. The BMW dealer just said "don't ever lose that key" otherwise I could never get the car to start again. They also did not charge me for their efforts. It seems strange to me that someone with a little computer/electronics savvy could not get a new key to work with this car. Is it true that it is impossible to program a replacement key to work with my transponder even though it is not the one that originally transponder with this car? By the way, that's the best I can describe the situation as explained to me by the dealer, and I'm still not sure if I am explaining it right. Thanks for any advice.

FCPGroton · 10-06-2009, 08:30 AM

I am surprised they could not figure out the code for the car from the working key. Can't they put it in a device that will read the key and then program that to the new key?

kstesney · 12-02-2009, 12:22 PM

I don't completely understand how the the BMW ignition key system works, except that it has something to do with a chip in the key and a transponder somewhere in the car. Also, some programming through the computer somehow might be necessary. It seems that maybe the chip has to match up with the transponder somehow. I could not believe that a BMW dealer having a working key in hand for the car could not make another key work with the car.

marti5 · 12-02-2009, 01:38 PM

The transponder is in the key fob not in the car, if your new key has no transponder in the fob it will not work, did the dealer take the fob apart to see if there was a transponder in there??

kstesney · 12-03-2009, 08:33 AM

I did not really understand the dealer's explanation of the situation. I gave him my spare key that I bought separately on ebay. That key was successfully programmed to open and lock the doors and trunk by pushing the buttons. Carsmax cut the key blank to fit in the ignition and it turns the ignition but nothing happens. They could not get it to work. The dealer tried and since the car has been rebuilt they said something about the duplicate key not being able to be programmed to work with the car. I still do not understand why. I don't know what the mechanics did when they rebuilt the car that would stop a duplicate key from working. BMW said that when they put my original key in some sort of reading device it was not the original key that should match that vehicle ID. In fact, they said something to the effect that not even BMW could make another key for me that would work with the car, and my best bet was to make sure I "never lose the key" I have, otherwise the car will never start again.

mkwame · 12-03-2009, 08:47 AM

To fix this problem correctly you'll need to replace your DME, dealer will charge about $1300 including programming and getting you keys that came with your car based on the VIN. Or you can buy a used DME, EWS and key cylinder with required keys from a junk yard for the doors and trunk

kstesney · 12-03-2009, 08:53 AM

Thanks for the explanation. What is an EWS? Also, I wonder how it is that the key I have now even works with the car considering it does not match the VIN?

mkwame · 12-03-2009, 09:38 AM

The EWS module controls the signal from the key to the injection system. If the key doesn't match the stored code in the EWS brain the car will not start. EWS is located under the steering column

kstesney · 12-03-2009, 10:01 AM

OK, that explains it then. I will see if I can locate those synchronized parts at a reasonable price somewhere. If not, I will just have to live with one key. Thanks for your help.

mkwame · 12-03-2009, 10:06 AM

what year and model bmw do you have?

kstesney · 12-03-2009, 10:11 AM

2003 325i

mkwame · 12-03-2009, 10:50 AM

i've got complete set of what you need from 2004 325i sedan but don't take my word check with the dealer. Ask them how will you ever get this key done right and they'll tell you you'll need to change the DME, EWS/CAS.

You may call me anytime 860-328-0908

kstesney · 12-03-2009, 11:47 AM

The 2004 parts will work in the 2003 model year?

mkwame · 12-03-2009, 12:20 PM

02-05 model year all the same