'12 G37 with Brake Booster Vacuum Leak

Dentt42

Vehicle: 2012 G37S, RWD 6-speed manual

I've been chasing this on and off since last week, and every time I think I've figured it out, it's a dead end. At idle, there is an audible constant hissing coming from my brake booster. Locating the point of the leak itself is driving me up a wall, and I'm hoping for some guidance.

So far:
-Capping the hose from the intake manifold to the booster stops the noise completely, so it's definitely the booster itself that's leaking.

-The hose grommet at the connection from manifold to booster is not leaking. I've replaced it and even tried sealing it with black silicone to make 100% certain, and no change.

- The booster sensor (connected by a second smaller hose to the booster) is not leaking. I can unhook the second hose at the sensor end, and capping the hose itself does not change the sound.

- The brakes lose power assist as soon as the engine is off, so the booster is not holding vacuum for any duration of time.

- The clutch master was replaced by a shop 10 days ago, and I noticed the problem very soon after. I usually do my own work, and circumstances forced going to a mechanic.

-The leak is bad enough to repeatedly trigger lean codes P0174 and P0171 for banks 1 and 2.


Do I have a bad booster? If so, how do I test it before removing it from the car? Going to the shop I chose meant calling in late to work to drop it off and then again to pick it up, and my boss complained.

Thanks for reading if you made it this far.