I have a 2000 c5 a6 2.7t 6spd and it drove fine this morning around 1pm. Just recently at 9:30pm as i went to start it i found my key (i only have one key) unable to unlock the door, i would insert it but could not turn it either left or right (my keyless entry has been inoperable for several months either due to a dead key fob battery or some kind of recognition issue, but I have always been able to lock, unlock and start the car). I am still able to unlock the trunk, so by doing that i climbed through to the drivers seat and tried the ignition. When i press the clutch and turn the key all the way forward the alarm goes off, when I turn the key to any position but the start position everything is normal and all accessories power on. This seems to me that somehow my key is not being recognized as valid, but I have no clue what the fix for this might be. The only unusual circumstance is that today the temperature dropped from a normal 30f to 15f. I am hoping there is something I can do that does not involve a house call from a dealership, I have a usb vag-com, any and all suggestions are greatly appreciated.

 

You don't need a vag-com for this. Your lock has frozen up due to the cold. Go to the auto store and see if they have some sort of spray or something to free it up. I've never had this issue as I've always lived in warm weather so I can't help you there.

Other than that its operating as it should is sounds like. The keyless entry would be the quick fix (or just avoiding the problem) but in order to reset the recognition after changing the battery you will need to be able to use the key in the door once. The battery is really easy to change by the way. I'd get that done as soon as possible so you don't have to deal with this issue again.