vacuum pump circuit for brake servo shorting out
 

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 this site that state(https://volvoforums.com/forum/volvo-...sensors-98208/) with 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

interesting, I think there may be a connection here. If you are leaking vacuum from the engine through the pump/hoses then that could cause an intake air leak that will set off the CEL (and flag the O2 sensors for being "out of range" as they can't compensate for the added air). That would also suggest something more than just a sensor is going on.

I'm thinking that you don't really have an O2 sensor / cat problem - if you don't have voltage to them (because of the blown fuse) they're not going to work right (at least until they're fully warmed up and you computer has already thrown another code).

In a case like this, it's a whole lot easier to just hook up an ohmmeter (a function on just about any multimeter) and measure from the non-battery side to ground. You'll almost certainly see a too-low resistance on that circuit (I'd guess under 1.0 ohm). Then the trick is to just start unplugging things until the resistance goes up dramatically. Then you know you've found the problem, and can save shotgunning (expensive) components looking for the problem.

Another option is to just wire a light bulb across the fuse connector - if the lamp lights up full brightness, you know you have a dead short to ground, and can troubleshoot it the same way (unplug things until the lamp goes out or dims noticeably). I'd say a typical brake / turn signal lamp would be a good choice for this.

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... However new issues have presented themselves. New code came up System too lean. I have also noticed that the throttle body was making a hissing noise when the key is turned into the on position. I don't think that I have ever heard a noise coming from that device so I have priced out a refurbished one and see if that will do the trick.

This new code was triggered after an oil change, and oil pressure sensor replacement.

Chase down the source of that hissing noise, and you'll find your remaining (new) problem. I'm betting there's nothing wrong with your throttle body (at least not that would produce a "hiss"), but that you've probably missed hooking up one of the million or so vacuum hoses when working on something else.

It can be a little difficult to ID the source of a noise like this sometimes - it can help to use a few feet of hose of some type as a stethoscope - that way you can really discern where the hiss is coming from.

I used a 2ft hose and the noise was coming from the throttle body more specific area was the side of it where the electronics plug in.

did you spray around with some carb cleaner etc to see if it gets sucked in and bumps the idle? that will help find an air leak, otherwise a smoke test may be in order.

Yes I sprayed all around the air intake manifold with carb cleaner but did not heard the engine change at idle. it continued to run rough on idle. Could it be the MAF sensor? Looking at the MAF sensor it is marked with some marker indicating that it was replaced from the junk yard at some point in the past by the previous owner.

It would be also worth mentioning that I might have a small exhaust leak before the catalytic converter. I think I can hear it when I first turn on the car..