3dmatters2us

Hello. I am proud to be joining the ranks of those lucky enough to own an A8! Mine is a 2000 with only 130k on the clock. Love it so far. Should have gotten one years ago.

I am trying to diagnose the speedometer drop out issue. I think others have seen this before. When mine drops out (not often), it takes the fuel gage down with it. I'm an electronics guru, so I pulled the cluster apart looking for cold solder and touching up solder on the gauge motors. This did not solve the problem. My instincts tell me to replace electrolytic caps (due to their age). Before I get down a rabbit hole, I would appreciate some advice on this issue.

To "pay it forward", I redid the rear brakes and relubricated the caliper slide pins with great success, so if anyone has questions about that, let me know.

Thanks!

3dmatters2us

Update: The speedo stopped working all together. I located and pulled the VSS. Since its a simple magnetic reed switch, I hooked up an OHM meter to it and passed a magnet next to it. This allows me to see it working properly (when the magnet passes next to it, the contact closes). Seems to work OK. There are two wires on the connector. Brown/Yellow and Yellow/White. Based on all my research, it looks like one goes directly to the instrument cluster and the other may pass through a pull-up resistor and to 5V DC (to generate the pulses). Now, since I'm a noob to this car, I need to find out what connector/pin assignment the signal wire comes into the cluster. Anyone have the instrument cluster schematics and can share some knowledge? I would appreciate it. Thanks everyone!

audinutt

On my a4, the magnetic ring inside the diff failed.

Not a horrible repair, but before you start chasing your tail make sure that it's working.
It might not be the cluster.

3dmatters2us

Thanks! I did finally figure it out. It looks like the previous owner had been into the dash before me. The scratches on the cowl just below the cluster should have been a clue. There was a bent pin on the blue connector. After straitening it out, the speedo has been perfect for over a week now. Go figure. I cannot believe I did not look at that when I had the cluster apart. Oh well, learned a lot about how the system works. Thanks again for chiming in!