Your post doesnt give many details, (such as which warning light it is, where on the dash, colour of warning light etc).
However, i am very very confident that this is the most popular and over reported item on this forum. (especially this time of year).
let me guess: red flashing warning light on the temperature guage, bleeps when you start up, or 20 seconds afterwards, bleeping doesnt continue, flashing light might though.
yes? - then its the coolant level warning. - true or false reading.
Often mistaken for oil or temperature issues as its on the temperature guage.
If you take the top off the coolant expansion tank and look inside you should see two metal prongs from the electrical connection area.
These prongs detect the existance of coolant and as such confirm the level. (presumably by the coolant providing a contact between the to metal prongs).
Now, it could be the coolant level is too low, and the sensor is working correctly. So first things first check the coolant level.
Or it could be that the coolant level is within the correct range, and the metal prongs are within the coolant.. but the connection or contact between the prongs is not sufficient enough as coolant levels are lower when its cold.
My advice is top the coolant up to the top of the range indicated on the expansion tank when cold. (will be above max when hot, dont worry this is fine).
YOU MUST USE THE CORRECT COOLANT, - G12 from a dealer, GSF etc... (its red or pink) or a VAG spec coolant from elsewhere, (still red/pink).
Do not mix with other colours or types. 50/50 coolant/water mix.
If this doesnt solve it the next thing will be to check if there is a build up on the metal prongs, which may reduce its efficiency so gently scrape these clean.
Then after that perhaps unplug the electrical connector and ensure all contacts are clean and make good contact.
After this, it would be replacing the expansion tank. (no you cant get the sensor on its own).
Id say 9 times out of 10 topping up the coolant will fix it. A very common fault.
If you doubt me, then use the search facility.
