Does this V70 Need a Cat? ECM-4801

[burnout8488]

Mother in law's 04 V70 2.5T FWD. The car has a P0420 / ECM-4801 code, goes on and off.



Oddly, my scanner does not show units for the front O2, but will show rear O2 voltage and waveform. The front O2 stays pinned at "1" while idling, but the rear O2 seems erratic. This photo was taken with the car at operating temp and idle, and a brand new Bosch front O2 sensor.

I have not replaced the rear O2 yet - trying to determine if I should, or if the catalytic converter is shot. There are no other codes, vacuum leaks, or exhaust leaks pre-cat that I could find.

Thoughts? Any other data I should pull to help diagnosis?

Thanks!
Alex

[oragex]

Downpipe flexible is prone to leak and may foul the 2nd O2 sensor. The cat may fail due to mixture burning issues, so a new cat may also fail. IFor the cat, best way is a used one, aftermarket ones give O2 codes. And a new Volvo one..

[burnout8488]

Downpipe flexible is prone to leak and may foul the 2nd O2 sensor. The cat may fail due to mixture burning issues, so a new cat may also fail. IFor the cat, best way is a used one, aftermarket ones give O2 codes. And a new Volvo one..

I always try to rule out *why* the cat may have failed first, perhaps bad plugs, perhaps poor ownership, but this car has had a nice life.

It seems quiet with the hood up, but I will give the flexpipe a closer look next time if the new Front O2 sensor doesn't clear up the CEL.

The rear sensor waveform just looks wacky to me though - it's a different voltage every time, and it sweeps at random intervals.