One problem related to brake master cylinder has been reported for the 2003 GMC Envoy. The most recently reported issues are listed below.
The contact owns a 2003 GMC Envoy. The contact was driving approximately 25 mph applying pressure to the brake pedal when the vehicle became difficult to stop and the brakes would exhibit an abnormal whooshing sound. The vehicle was taken to an independent mechanic who advised the contact that there was a leak in the master cylinder and the power brake booster. The technician replaced the power brake booster and the master cylinder. The vehicle was repaired. The approximate failure mileage was 117,000.