Hi. My daughter bought a 2004 XC70.It was bought at 99,000 and now has 103,000.So far I've done the brakes and spark plugs.

The problem is code P0420 which has come on a few times and the car is running very rough.O2 sensor and catalytic problem.

The autozone readout says possible timing error.Could the timing belt jump and cause a timing error?

It also said possible oil in the cylinder.When I changed the plugs they were not sooty.Have I eliminated that possibility?

It looks like O2 sensor replacement and possilble cat replacement.Is there a good aftermarket cat?

Any ideas on the source of this problem? Thanks.

 

I hope this helps http://www.obd-codes.com/p0420

 

Thanks for the link.