My dealer told me (lies ??)

[rAudiman]

My local dealer told me that I should not replace the BOSE (Symphony) head unit in my 2000 A4 2.8 because much of the car's computer function is dependent on that circuitry. They went on to claim that they have had a number of cars come in with strange or squirrely electrical &/or display problems due to exchanged head units. Is this crap or is there something to it? I really want to get an MP3 unit in my car... please help. .\\ikeQ

[T-28-Quattro de VT]

i replaced mine with a sony active black panel and i havent had a problem and have had it for a week.

[WClark]

...for instance it is part of the VAG system, it gets inputs from the ECU for speed and it shares some circuitry with the cell phone system. It also has an interface to the instrument pod wher it shares display space with the ECU. I think it also interfaces to the security system.

I guess it is possible that an installation of an aftermarket head unit could leave some interfaces unterminated and picking up electrical noise which might interfere with the data exchange among the remaining systems causing funny or intermittent problems.

[MoBrazen]

The K wire is the interface between all of the electrical systems in the car. All you need to do is (1) cut it & cap it off from the new head unit or (2) not include it in the aftermarket harness. If you do a search for "K" wire, I know it will come up (because I'm usually the only one that posts about it.) Just so you know, I had a local dealer tech work with my installer to properly identify the wire & provide all necessary schematics before the install. The tech is also a customer of the installer, so this is first hand info.

[Richard Solomon]

It's the K-wire they're worried about, because old bad harnesses which tie it to 12V will blow the dealer's diagnostic equipment if they hook it up. MoBrazen's absolutely right about that - just don't hook it up.

I believe the '00+ cars at least use CAN bus to communicate all the cool stuff (vehicle speed, instrument cluster displays) to/from the radio. On those cars, the K-wire is inactive until diagnostic equipment (1551, 5051, VagCom, etc...) is connected to the car's diagnostic connector.

I don't know what implications dangling the CAN bus connections would have...other than plenty of '00+ folks have replaced head units w/o difficulty, so either they're connected correctly in aftermarket harnesses or it doesn't hurt to dangle 'em. Maybe both.

Short answer. Like MoBrazen says: make sure your harness doesn't tie the K-wire, and you're probably golden.

[2phast]

those schematics? I sure would like to borrow them........

[MoBrazen]

[2phast]

*

[rAudiman]

Did you happen to find those schematics?

[MoBrazen]