Brake booster vs vacuum pump

sbateman13 · Post by **sbateman13** » 30 Oct 2016, 11:20

Hello,

We are trying to fix a problem with my 2003 Volvo S40. My husband has been able to do most of the repairs to this vehicle himself, but this time we are having trouble isolating the problem so we know what parts to order.

There is probably more than one problem, but here is the synopsis: Loud and annoying buzzing/humming sound with braking difficulty. Occasionally car will stall following hard braking or a sharp turn. Based on my research so far the noise is probably coming from the vacuum pump. Check engine light is on (and has been for a LONG time).

Because of the check engine light, the stalling, and also the unpleasant fumes from the car, I am pretty sure we are looking at at least two separate issues, but for the purposes of this post, I am focusing on the safety issue which is the brakes (and the annoyance factor of the super loud buzzing!).

What is unclear is whether we need to replace the vacuum pump itself, or just the vacuum pump hose, and whether the brake booster could also be bad. How do we tell which of these is to blame for the problem, short of buying each part and replacing them one at a time? I have even read that sometimes a new brake booster gasket is all that is needed... Anyway, we finally have some money for repairs so let's figure this one out!

Thanks in advance for any assistance you can offer!

Post by **jimmy57** » 30 Oct 2016, 11:24

Look for blown fuses. The heated crankcase breather fitting where crankcase vent hose meets air cleaner to turbo inlet hose can short and blow a fuse that stops electric vac pump and idle air control valve function.

I can't remember fuse number. You can unplug the two wire connector for the heated nipple. It needs to function if temps fall below freezing as the moist vapors freezing in that fitting will increase crankcase pressure and pop out cam and crank seals.

sbateman13 · Post by **sbateman13** » 30 Oct 2016, 12:39

Thanks for your reply. I have no idea what you're talking about but I'm sure my husband would, ha ha! So you think if a fuse is blown and we replace it that would fix the buzzing sound coming from the vacuum pump? Is it relevant that we live in an area where the temperature rarely drops below freezing?

I am just wondering if the buzzing sound means for sure that the vacuum pump is now failing and should be replaced...

sbateman13 · Post by **sbateman13** » 31 Oct 2016, 11:45

Bump.... Anyone else have any insight?