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Discussion Starter · #1 ·
when redoing my car stereo with the help of my friend, we ran into a lot of "firsts" with my car ranging from crossovers built into amps to the way we had to run wires from point a to b and etc. Now i have run into a new first and i'm hoping someone can help me with it.

living in the great state of california, and my car now being 4 years old, i have to get my smog checked. i figured this would be easy. i take good care of my car, i have never missed a service, and so on. boy was i wrong. i got to the auto shop and they told me that my onboard computer was not communicating with the smog machine which is an automatic fail. so now going from a proud VW owner, I am now getting annoyed with my car since I have had to deal with lots of other little random things that have taken their toll on my wallet. they continued by saying that they had seen this before with aftermarket decks being installed - and thus why i am asking about smog in the audio forum. they said that there is a low level bus signal that is either sent roundtrip to the deck and back or from the deck, i wasn't quite sure, but bottom line, changing decks means there is no more bus signal. and no more signal means my computer now doesn't want to communicate with the outside world. this confused me a little but i thanked the guy and now i am in the process of getting my factory deck shipped back to me, thank god i saved it.

with this, i ask two questions. 1) can some explain what exactly is going on with this bus signal and why there is something this retarded in a car? I mean i am an engineer so low level signals aren't foreign to me, but i dont know much about cars, so the concept of having one in my factory deck in some way so my onboard computer will communicate with the outside world is. 2) what can i do about this? is there a way around it without wrestling with my factory deck, getting my smog checked and then spending twice as long wrestling with my new deck to get it back in? if i do have to install the deck, do i just need the deck or do i need the whole system up and running? i ask this because we clipped all the wires to the amp so those huge plugs were gone and so the wires could be tired and hidden.
 

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Check the connections on the aftermarket wiring harness adapter. Sometimes the diagnostic wire (k-wire) can be looped to power or ground (don't remember) on some of the older harnesses. Compare the wiring diagram sticker on your factory radio to the wiring harness that you bought. If you see a connection (loop to another pin) at the k-wire location cut it and tape it off. Nothing should be connected to the k-wire.

I ran into the same issue on my 1998 B5 about 5 years ago when I brought my car into the dealer to have them reprogram the doors to auto-lock. This will hinder any scan tool talking to your car.

-Mark
 

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the older "Metra" harness linked the k-line
which is the diagnostic wire for the stock radio.
this is used to communicate with the ecu for
troubleshooting the radio.

dont sweat dude. this wiring mis-hap happens
quite often when the k-line is carefully looked for
and taped off. :wink:
 

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ohh, by the way, you Can destroy a Vag-1551
diagnostic tool at the dealership when the k-line
is grounded or powered. they sometimes will
not scan your car for problems when you have
an aftermarket radio.

the Newer Ross-Tech Vag cables have an Led
in the plug that turns red when theere is a k-line
miswire 8)
 
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