99 Audi A4 Avant Audio Wiring

I'm looking for information to install the pioneer NAV-Sys910DVD or another navigation and/or DVD player in a 99 audi a4 avant. This isn't my car and have never installed in an audi. My friend told me that his old head unit he had in there used to mess up the ECU, it would give fake codes, and false codes, he would have to remove the head unit if something went wrong to check the code. Im wondering why this is, and is their some specail way to wire in a head unit/DVD/Navigaiton system. Hes not sure what hes going to get yet. He just sold his old system because it messed with the ECU(or so he said, i never saw it). Any and all help would be great.

Thanks a ton,

Mark Sprague

You would only have problems if you hook up the wrong wires. 2000 and newer A4's have a dual k-line on the OBD II plug. Hooking up an aftermarket deck could backfeed 12v into an Audi techs VAG1551 frying it. Your friend must have a newer A4 and needed to remove the deck because most dealerships that see non oem won't touch the car.