2004 be jetta
 

I ha e a 2004 be Jetta and the ECM went bad so I got a used one with the same serial number, I am wondering do I have to get a new key made?

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After being prompted. ;)

You will need this new coding but you need to find the Secret Key Code (SKC). As far as I know that can only be found with VAG TACHO.

The key is just a blade its the coil around the ignition switch that has to be coded.

You can ask at a locksmith if they can code a key?

Please tell us your car spec in your signature