I just changed my brake booster because I was getting the hissing sound coming from underneath the dash. I was able to pick up the booster from a recycler for $100.

The hissing has seemed to stop. However, I am still having an issue with the vacuum pump assist. The pump will cycle for about a minute after the car is turned off. This problem started when the hissing sound started. I was hoping that by replacing the booster both problems would have been solved.

Any idea what is causing the pump to cycle after car is turned off?

Let me add, this is an '03 V70 with 170k on odometer. Base 2.4.
No CEL lights on dash.

Any input is greatly appreciated.

Thanks

 

Problem fixed. I was leaking air through the brake position switch. I am not sure if I damaged it upon installing the booster. Nonetheless, I swapped it with the switch from the original booster. No cycling of the air pump now.

 

Hmmmm,

This sounds exactly like the issue I just posted: "Hissing Sound from under the dash". I too experience run-on of the vacuum assist pump after shut down.

Did you ever determine if the initial problem was the booster itself or simply the brake position switch hissing?

Thanks

Bob