By "mechanic" do you mean "I can do it for cheaper"??? Cause that means you are fighting a guy for shoddy work rather than getting warrenty on a shop for the part... Getting a 2004 computer unfortunately will not resolve your issue here. It's that the trans you got plugged in is a different trans and the computer knows that. (Or maybe even it was installed improperly on the wiring side) 2004-2006 is the same era of crown Vic of this time. Get an electrical diag from a shop and see what they will say. My buddy had to replace his entire wire harness which was a total pain. Good luck. Also look up your current smog laws. California is hella wack nowadays. Idk if you be here or elsewhere.

Hi Thank you for the info.

The car was sold to me as "great car, brand new transmission,brand new tires" by my old neighbor who is also a mechanic working out of his parents backyard. I saw the transmission he bought it said 2006 with black marker on it but there was also a sticker on which said 2004.  I paid the fines on the car but never got a tag because I couldn't get it smoged .....well long story anyway at this point I don't know what to do I had to go to court because of this but got a extension to fix it till the end of this month. Anyway thank you

Welcome to The Hotel California.

did california at some point become a police state?

sounds like it