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?

 

Welcome to the forum.

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