2003 XC70 - Crank wont start Fuse #3 keeps blowing

[AutosDirectFlorida]

Like the title says, we have a 2003 XC70 and for no reason one day it wont start.
Found that Fuse #3 for the vacuum pump/bifuel dfco keeps blowing as soon as you turn the key on.
Is this fuse related to the car not starting?

What can we look at in regards to the DFCO? I have no idea what this is.
Google has not been friendly with this search.

Thanks.......

[AutosDirectFlorida]

While we still have no idea about Fuse #3, I believe the non start issue was related to a low battery.
I've never seen a car act this way from a low battery - would turn over - all accessories worked etc
When we finally hooked up the battery box, just because I wanted to, it cranked right up without issue.
Ran it for awhile and it recranked without issue.
Investigating battery issue and dont care about the vacuum pump - no messages or codes so far and runs great otherwise.

[Forkster]

I would check the alternator for voltage output - the voltage regulator will go BEFORE the entire alternator will actually wear out. It's an easy fix to put in a new regulator, but getting it in and out requires elbow grease and patience.

[hoonk]

2003 XC70 .Fuse #3 for the vacuum pump keeps blowing

That car has a vacuum pump for the power brake system. The plastic control switch breaks, gets stuck on and the vacuum pump over heats and melts from being on all the time.

You may notice the car does not stop well right after being first started (when there is very little manifold vacuum for the brake booster)