AUdi TT engine code P2181

Just acquired a 2003 TT Coupe for my daughter. Hd it 2 days; it's now showing a Check Engine light Took it to Autozone to get scanned, they tell me the code is P2181 and
that it means low coolant.
According to http://www.hallsautoonline.com/obd_ii_code_definitions.htm , it means "Cooling system performance""
BUT - coolant tank is showing 3/4 full. I tried disconnecting the battery for 10 sec to reset the codes - no change. I _did_ manage to reset everything else, but hte check engine light is still on.
Also - there's a constant hum from near the cooling fan - looks like a small inline pump in the coolant line. It doesn't seem to shut off - was running nearly an hour after we returned from the store.
What's happening here?
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Oh, BTW the temp guage reads fine while driving - just below mid-guage. The car is _not_ overheating.
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Check the coolant filler tank to see if it is low. If so fill with Audi coolant from the dealer. Do not use an alternative from the local parts store. There are alternatives but you would need to research which ones are acceptable.
If it looses coolant again you will need to find and correct the leak.
If the coolant is not low you probably have a bad coolant level sensor (located at the bottom of the coolant tank.
Frank Rowe wrote:

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I had the same problem on my 98 A4 so I changed the expansion tank and all was well after. It was most probably a faulty sensor in the tank.
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Hi,
We had two 1.8 TT coupes, and they both had an electric pump running after the ignition was switched off for a while. I never timed it to see how long. I believe that this pump is for circulating coolant through the hottest parts of the engine until they have cooled enough.
We had a 1989 Renault 5 GT Turbo that had an air pump that would run for up to an hour after the engine had been turned off.
HTH
David
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The sensors can get clogged up. Open up the expansion tank and there will be a couple of prongs in there, just rub them down with a screw-driver or something to get any gunk off them. Should resolve it.
Make sure you've had a cambelt & water pump change done on that car if it hasn't been done already.
Frank Rowe wrote:

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