2012 Volvo XC60 3.2 AWD. Bought with 25K miles, currently has 167K miles. Car has been bullet-proof. All I have needed to do is brake pads, oil, and tires. Check engine light never came on once. Car has always run great - 22 mpg around town and 24/26 on the highway.
Over the past year or so, car started getting louder - exhaust noise. When it warmed up, noise went away. I crawled under it and it looked like the flex coupling at the front of the catalytic converter was distorted, so got a hold of a muffler shop who could work with the stainless exhaust (no one locally can) and took it over to have the flex replaced. Turned out, the noise was a very cracked steel exhaust manifold. They said the reason for the crack was usually that the catalytic converter was partially blocked and that I would replace that as well.
I OK'd that, parts were ordered, and we picked up the car and headed for home. About 70 miles into the trip, the check engine light comes on. The error in VIDA-DICE (the Volvo diagnostic tool for independent shops and owners) said the Cat efficiency was below threshold. Call the shop and they recommend replacing the rear O2 sensor. Since the O2 readings were a little wonky, I replaced it. 70 miles in, the light is back on. Called the shop and they pointed to the wonky O2 sensor readings. OK, I say, let's fix this. Ordered the front and intermediate O2 sensors (all three were Denso OEM sensors), new spark plugs, and a PCV diaphragm repair kit. Installed everything and cleared the codes... which stayed out for 120 miles.
At this point, the only parts I can think to throw at it are new injectors.
The shop has a great reputation, so I really think they have been trying to do the right thing, but I suspect that the aftermarket cat is just not up to the job. I keep going back to the car never throwing a code before the new cat.
I would appreciate any ideas about how to proceed.
Thanks
