[kramerdude]

Hey GM lovers,my 2003 GMC 4x4 keeps stalling when I apply the brakes.Could that be the brake booster or the air booter pump?The pump works when you pull the vaccume line off and apply but the booster make a loud hiss sound all the way to the floor. 5.3 /z71/131k.

 

[nicolet]

Must be a leak somewhere in the system, as when pressure is applied it's too much of a load on the engine...

 

[kramerdude]

If I spray brake clean in the area to see if there is a leak is that o.k. ?

 

[mbukukanyau]

I would have the vehicle looked at by a mechanic, or dealer, do not operate it. It does not sound safe

 

[Slideways]

I've had the same problem before, it was a leak at the brake booster. You could try plugging the vacuum hose to the booster (on the booster end) and then pressing the brake, with the truck in park. That will at least tell you whether the leak is on the brake side or the engine side.