Loud engine noise

[onlyislandlady]

Car: 2006 Volv S40 2.4i 5cyl at 105,000 miles

First question: I had some engine noise and progressively kept loosing gas mileage over a period of 6 months. The dealer said there was a catalytic converter efficiency code. When they replaced the camshaft reset valve, the noise got significantly louder and almost sounds like my car is always on low gear for 4-wheel drive. Is it possible they damaged something when they replaced the camshaft reset valve to make this loud noise? such as a valve? or is it as the dealer says, the catalytic converter needing to be replaced?

Second question: can I buy the OEM aftermarket caty converter for this car?

Third question: Should I replace the O2 sensors also?

[FlyingVolvo]

I would think it to be unlikely that your cat converter would be dead with your model year and miles, although it can happen. Do you notice a big loss in performance in conjunction with the noise and lost gas mileage? If so, that could be indicative of a plugged or degraded cat. The old trick is to take a rubber mallet or something and bang the converter and listen for rattling or anything that would show that it has fallen apart. The noise could also be an exhaust leak of some sort.

You can buy the OEM converter from various sources, as well as appropriate aftermarket ones (depending on your state's emissions standards).

Replacing the O2 sensors at your mileage wouldn't be a bad idea, although I'd try and sort out any of the bigger issues first.