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Ross-Tech: VCDS: Afterrmarket Radio Problem

Somewhere between 1997 and 1998, VW and Audi started using diagnostics-capable radios in most of their models. That means the dealer's scan tools (and our own VCDS system) can talk to the radio. Why? So you can set various options, like whether a CD player is connected, whether there's an amplified or conventional antenna, and so on. In addition, these radios constantly monitor their speaker outputs and if you have an open or short circuit to one of the speakers, even a momentary one, they will record a fault code.

The problem is, VW brought the "K-Line", the wire on which all of the control modules in the car communicate with the scan-tool to a pin in the connector on which older radios used to put +12 back into the harness. (We're not sure whether this was for antenna power or as an amplifier turn-on or what). So if you were to take the non-diagnostics capable radio out of a 1997 GTI and put it in a 1998 (where there should be a diagnostics-capable one), it fits perfectly, plugs right into the harness, but the K-line ends up shorted to +12!​
Aftermarket Radios
Now people hardly ever put older stock radios in newer cars. What they often do is install better after-market radios. And they most often do this by using an aftermarket adapter-harness which plugs right into the car's harness, so they don't have to cut up the car's harness. Trouble is, some of the aftermarket harnesses faithfully reproduces the older, non-diagnostics radios with a loop of wire between +12 and the pin where the K-line is on newer models. So you install your fancy new radio with one of these and everything works fine until.. somebody plugs in a scan tool.​
The Problem
Nothing in the car cares if the K-line is shorted to +12. The K-Line is not used for intra-vehicle communications. But a scan-tool initializes a communications session by pulling the K-line to ground. The K-line is supposed to have some voltage on it, but through a high-impedance source. If the K-line has "hard" +12 on it, something has to give! What "gives" is usually the scan-tool's output driver for the K-line. And fixing a VAG-1551/1552 with a blown K-line driver is expen$ive! But the ISO-COM PC<->Car interface adapter that we provide with our VAG-COM software has a small user-replaceable fuse protecting the K-Line output driver, and there's a spare fuse taped under the lid of the little box. No big worries there..:) Our other interfaces use output drivers that are thermally protected against shorts. They don't need a fuse. If you plug them into a car with the K-line shorted to +12, they simply won't work in that car, but it won't hurt them either."​
I just installed a new Pioneer digital radio, which is working fine, but now my Auto-Polar display is gone :unsure:
Anyone else have any more current info on this issue?
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