vacuum pump circuit for brake servo shorting out

zippy83 · Post by **zippy83** » 04 Jan 2019, 19:48

Hi All,

I am hoping to find an answer to a mystery that I have been looking into for over a week now.
I have a 2006 Volvo S40 2.4i with a little but over 132K miles on it. About a week ago my check engine light came on, I looked at the code and it told me that both HO2 Sensors 1 and 2 are bad. I ordered two new sensors installed them cleared the code and 20 min later the same code re-appeared.

Someone at work told me that I may have a leak in my exhaust manifold, I inspected the Manifold and wasn't able to see anything. I did replace the upper and lower gaskets, with no luck at all. Then I read somewhere on the internet on a article that there is a fuse under the hood. Location #33. Sure as hek that fuse was blown. I replaced it, cleared the code and tried again. About 20 min later the check engine light came on again with the same issue.

I looked at the fuse and saw that it was blown again. Then doing some more research I came across an old post on some other site that states the same issue and that the problem was vacuum pump circuit for brake servo shorting out. Now I am not sure what Am I looking at here. The entire Vacuum pump or is there a sensor attached to it?

Any help is greatly appreciated.
Thank you
Zipp

Post by **abscate** » 05 Jan 2019, 23:50

Go to your owner manual and look up everything on fuse 33, you need to check everything on that circuit and find the item that blows the fuse.

zippy83 · Post by **zippy83** » 06 Jan 2019, 19:25

Hi there. After examining the vacuum pump I have noticed that it never comes on. And as soon as you tap the brake the fuse blows immediately. After replacing it with a refurbished vacuum pump the issue has gone away.

Post by **jimmy57** » 06 Jan 2019, 19:36

Now you need to monitor what is going on. The vac pumps I have replaced for failing, some shorted like yours, have been ones that ran too much due to vac leak, bad booster, or bad switch. The normal operation when engine is fully warmed up would be pump runs if you pushed and released brake a couple of times or more. The switch is more likely to be the problem from what I've seen.
Often you cn tell it has partly come apart as it will be crooked.
At high altitude it will come on more readily. WHen first started and CVVT is phasing cam way out of "normal" position it will have to run more.

zippy83 · Post by **zippy83** » 06 Jan 2019, 19:50

Thanks for the suggestion. I have noticed that the pump only comes on when you press the brake. Also after install when I turned on the engine it immediately came on and stayed on until I pressed the brake for the first time. After that it comes on only when I press the brake down. You do mention the switch.. Is the switch built in the pump or does it sit someplace else? If it's outside of the vacuum pump do you know the location?

Post by **jimmy57** » 06 Jan 2019, 20:06

The switch is in the black hard line that goes into firewall to get to the booster hidden there. It has a brown two wire connector.

zippy83 · Post by **zippy83** » 06 Jan 2019, 20:11

Thank you.. I will keep an eye on it. Hopefully it will behave..