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Cold weather brake problem on Audi-A4

What would cause the brakes on a 2002-AUDI-A4-QUATTRO-1-8-TURBO not to work in very cold weather(below freezing)? The brake pedal is stiff and won’t depress so the brakes don’t engage. After a half hour or more warm up they will work fine until the car sits out in the cold again for an extended period.

When was the brake fluid last changed? If the brake fluid has not been changed for 3 years/36k, then it needs to be done.

Brake fluid is hygroscopic, which means that it absorbs moisture from the air. The symptom that you have experienced is what happens to “old” brake fluid in the winter. In the summer, brake loss also occurs, but in that case, it happens when the brakes are heavily used, as in mountain driving.

The bottom line is that those who do not change their brake fluid at least every 3 years will risk the loss of braking ability in a variety of climatic conditions.