Q I have a 2000 Subaru Outback. It has been a great car and has about 96,000 miles on it. The problem relates to the brakes and happens only in the winter when the temperature stays below freezing all day.
During the day at work my car is parked in an unheated parking ramp. At the end of the day, when I go to back out of the parking space, I find I have no brakes. Even with my foot on the brake pedal as hard as I can, the car continues in reverse without stopping. I learned quickly to back up very slowly. It has happened the last two winters, and today with the temps below zero all day it was really bad.
Today, for the first time, the brakes did not work when I drove forward, either. I press down on the brakes and nothing happens. Last fall, I had a major brake job done on the car and figured with new pads and everything the problem would go away, but it didn't. I have the problem only when I come out of work after the car has been parked all day in this ramp.
The car is in an attached garage at home, and I don't have any problems in the morning. The problem disappears after a few minutes of driving. It's almost as if ice has formed on the brakes.
A When this occurs, does the pedal sink all the way to the floor? Or is the pedal firm and at normal height, but no stopping power? Is the "Brake" or "ABS" warning light on? Or both?
I checked my Alldata database and find no bulletins on brake system issues like this. You may be right in that something in the system is literally freezing solid. If the brake pedal feels firm and normal but the vehicle won't stop, perhaps moisture in the brake fluid is freezing and preventing the brake system from applying hydraulic pressure to the individual wheel brakes. Remember, hydraulic brake fluid is hydroscopic, meaning it will absorb moisture from the atmosphere over time. This is the No. 1 cause of contamination of brake fluid and corrosion in brake system components.
Since your vehicle is now six years old, I think your first step in trying to resolve this problem is a full and complete "bleed/flush" of the brake system to exchange 100 percent of the original brake fluid with new brake fluid. Many carmakers call for routine brake system bleeding/flushing every couple of years -- a maintenance suggestion I fully agree with.
If the brake pedal sinks to the floor during this loss of brakes, try several quick pumps on the pedal as this occurs. If the brakes suddenly "catch," the problem may well be a worn or noncompliant cup seal in the master cylinder allowing a bypass leak of brake fluid upon initial application, or a stuck hydraulic valve in the antilock-brake system allowing a bypass of fluid and pressure. I would think that if this were an ABS-related issue, the ABS warning light would come on and an ABS fault code would be stored in the system.