Models: 1998-’99 Legacy Sedan, Wagon, Outback, Forester.

Problem: Hard brake pedal (high effort) in extreme cold weather. Braking ability gets better as air temperature rises.

Cause: The vacuum hose in these vehicles has an in-line check valve (see graphic). Moisture can accumulate in the valve. In cold weather, the moisture freezes, blocking the vacuum to the booster, which causes the need for greater brake effort. When the air temperature rises above freezing, the valve thaws out and normal brake effort returns. 

Solution: Inspect hose and check valve assembly. If moisture is found, the source of the moisture must be eliminated. Check the emission system and the engine for proper operation; correct or repair as necessary. It may be necessary to replace the vacuum hose and check valve assembly to correct the freezing problem.

 

Source: CARDONE Pro Tech