My 2006 Volvo S40 2.5l T5 AWD manual transmission received and o2 sensor heating and voltage issue check engine light and codes. I took it to a specialized volvo mechanic and he told me one o2 sensor is not heating up and the other is causing voltage irregularities causing fuse 33 to blow (o2 heater sensor and vacuum pump fuse) Ok so I replaced my up and down stream sensors with bosch o2 sensors like he recommended. My fuse was fine for a couple days and blew again. I replaced it and it was fine for a few weeks before blowing again. Now it's been fine for more weeks but no matter whether it's blown or not my car runs like crap with no check engine light. Very delayed throttle with rpms jumping up with little power and then dropping down and then the power initiates.

It's annoying the fuse takes random times to blow and I've thought of replacing the electric vaccum pump and switch which shares the fuse with the o2 heater sensor that keeps blowing. Someone online with the same fuse 33 blowing out issue said they replaced the vaccum pump and it fixed the car running lean/rich, but their car only accelerated with jumping rpms when their fuse was blown, while mine does it no matter if the fuse is blown or not. So now while the car drives like **** and there is no check e gine light and the fuse is ok so far, I don't know what to replace or do.

A mechanic with German car experience, not volvo, said it most likely is the vacuum pump causing the short and blowing out the fuse.

Is it possible the car is running like crap because the fuse is not working properly? maybe voltage issues due to the vacuum pump and this is why it shorts at random times?

If it was the EGR valve or carbon build up or bad sprak plugs or connectors wouldn't there be a check engine light?

To add, idle and downshifting the RPMs are fine.

Any help would be greatly appreciated. 🙏

 

Have you checked for any intake leaks? Check the hoses connected to the vacuum pump as well. You have vacuum at idle so the pump wont be running then. Check the vacuum pump switch as well.

Not everyone has access, but I like doing a smoke test for intake leaks.

I had my intake pipe come off and didn't get a CEL.

 

I've checked the vacuum pump switch and it's fine. Had a mechanic inspect it for free too, looks good. When I turned my key for power (not starting engine) I checked to see if vacuum pump is running. My brake pedal gets hard so this means it's not turned on before ignition. I will check for leaks but I think it may be wiring related, electrical due to the shorting of fuse 33.

 

I found a link that says fuse 33 goes to the heater element of the O2 sensor. Have you seen any related codes? If you pull that fuse, what codes do you get?