4Goffs

I have a 2011 Grand Cherokee Limited 4x4 with 47k miles.

When trying to stop i can hear hissing in the cab & my brake pedal gets real stiff.....Now i spoke with my mechanic & he told me it sounds like the brake booster but when i took it to him with the part for repair the brakes started working fine. The computer also gave no codes during the 30 minutes of driving it was hooked up. The brakes also didnt malfuction as they were the previous 2 days before.
To make matters worse i drove to work today after doing all the tests last night & the brakes are getting stiff/hissing again.

I live in Ohio & its been cold so it seem that this issue only comes up in the morning when i leave for work & in the evening when i go home.

Has anyone heard of this issue? Again the Jeep is not throwing a code & the issue only happens when its cold. I need to fix this before i need to make an emergency stop & cant due to whatever the heck is going on.....this is ...

red4dr

it does sound like the booster. I know we had the master cylinder go out and it made the pedal just fall to the floor and stay there with no brakes. The booster would sound right because it helps you apply pressure to the brake system making it easy to push.

JWheeler

Yep. Brake booster. The seals go out and it will leak vacuum and cause the hissing sound.