Hello all, I am a college student fresh to these forums as I just last month bought a 1996 Volvo 850 Turbo. It has 146k on it, and runs great, except for last week when the CEL came on. So I had it read at autozone and I got the P0422 code stating:

Main Catalyst Efficiency Below Threshold (Bank 1)

Now the car started and ran fine for a few days, but I took a 4 hour trip to Chicago last weekend, and ran into the following issues.
-The mpg's on the trip computer would on and off go down horrendously.
-The car sometimes would violently shake back and forth while I had it on cruise.
-It really seems like something's a miss with the turbo as well, the gauge moves, but I really feel like I shouldn't be flooring it until I have this issue resolved.

I have done a bit of reading online and I dont know too much about cars, but I really feel like this is an oxygen sensor issue. I really hope it isnt a CAT problem as this would most likely be quite a bit of money to fix.

So does anyone know anything about this code, or these symptoms? What could this all be a result of? And if it is the Oxygen sensor(s), how easy is it to replace them yourself?


Thank you!!

 

Could be the O2 sensor but I would also check and see when the last tune-up was. It might need a tune up.