Failed smog check b/c aftermarket stereo and check engine light
 

I took my 2001 a4 into a smog check station yesterday and was told that it failed for two reasons: (1) the technician couldn't communicate with the car because of aftermarket stereo work that was done, and (2) the check engine light was on.

Any idea how I can unblock the communications and also, do I have to take my car in to a shop and resolve the check engine light situation before I can even pass a smog check?

Thanks in advance

you don't necessarily have to take the car to a garage. Pep Boys or Autozone or any other auto shop should be able to read diagnostic codes. That will tell you what the reason is for the CEL.

I have never heard of a stereo interfering with communications though. Maybe someone else can help out with that one.

From my understanding there's a bus line between the radio and instrument cluster that needs to be connected or else the two won't communicate. When installing an aftermarket head unit, this line can get eliminated and apparently if it's not connected then a code reader wont be able to read codes...I've heard of this issue before but I'm not sure how to get by it

Funny story...
I had a similar issue with my aftermarket rado (piaoneer 4200 I think..)

Turn's out that all I had to do was remvoe the radio head unit (the piece that all robbers take when they break your radio; candy abr piece that pulls of with the press a a button).
By doing so, and I don't know why! The obdii's could easily communicate with the car, but if it was plugged.. the machine would get a error.
That's what solved my problem..

Yup, i have my stock bose concert w/ an aftermarket wiring harness for my sub and amp. I also cant get any readings off of the system with the harness in, but if i take it out it works fine. I've read off ross-tech that it has to do with a k1 line. I tried a work around but it didnt work for me. There isnt too much documentation of it online. i really wish i could figure it out tho. Its either vag-com or lots of bass! and i love them both.