My Dad has a 2005 A8. On a number of occasions when the car has been parked for the night the break lights will come on all on their own. He has gone out to check before going to bed and they are not on but the break lights will come on hours later for absolutely no reason. He has checked the floor mats and they do not seem to be the problem. Any suggestions as to what the problem could be?

We have had A8's do that before at our shop, most of the time its a malfunctiong brake light switch. Its the sensor that connects to the pedal.

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00 A4 1.8T

01 S4 SOLD!!!

That sounds like it is probably the culprit. Is there any way that he can or have the mechanic (he is not an Audi mechanic) test thisswitch/sensor to see if it is defective or should he just have it replaced?

There is a way to test it with either the VAG COM or VAS factory scan tool. You would have to go to data block 2 in the brake electronics and slowly depress the brake pedal to watch the detents engage one after the other.
The other cause since its such a highly complicated vehicle is a module that is faulty, which has also happened for this same complaint, the best possible thing to do is have the dealer look at it.

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00 A4 1.8T

01 S4 SOLD!!!