autocheck coolant warning

[George Selby]

The coolant either low or overheat warning has started coming on in my 90 Audi 200's autocheck system.  It's not low on coolant, and it's not overheating.  I have tried the three different multi temp switches (2 three prong, and one 4 prong) I have, and they all do the same thing.  When I first start the car, it won't come on, but within 1-5 miles it will start flashing.  Sometimes it will go out while driving, but then comes back on.

I have tried unplugging the multi temp sensor, and the coolant low sensor in the overflow tank (separatly, and at the same time.)  I have also just unplugged the blue/yellow wire from the multi temp switch - this results in an immediate flashing of the warning.  The only thing I have noticed makes a difference is when you unplug the multi temp switch, then plug it back in the light will go off a couple to 30 seconds, then start flashing again.

How does this system work?  I figured unplugging both sensors would make it stop, but unplugging the coolant tank switch seems to have no effect, and unplugging the multi temp switch makes the light come on instantly.  Are there any other sensors associated with this warning system?

George