'01 Forester P0420 help

[overflow23]

I have a 2001 Forester that has a P0420 code with check engine light.
I had both catalytic converters replaced with both O2 sensors
replaced. Two weeks later, the code is back. Then I had a tune up
(plugs, wires, PCV valve) and 1 week later, P0420 is back.

What else could be causing this? Or do you suspect that one of the O2
sensors from Napa is bad? Catalytic converters were rebuilt, but they
are 49 state legal so I wouldn't think that was the problem.

I'm getting frustrated with my local shop, though they are trying.

 

[Carl 1 Lucky Texan]

I have a 2001 Forester that has a P0420 code with check engine light.
I had both catalytic converters replaced with both O2 sensors
replaced. Two weeks later, the code is back. Then I had a tune up
(plugs, wires, PCV valve) and 1 week later, P0420 is back.

What else could be causing this? Or do you suspect that one of the O2
sensors from Napa is bad? Catalytic converters were rebuilt, but they
are 49 state legal so I wouldn't think that was the problem.

I'm getting frustrated with my local shop, though they are trying.

Well, some folks have suggested that aftermarket O2 sensors are inferior
to OEM.

I think it's your shop's responsibilty to actually troubleshoot the
problem. There are oscilloscope tests for sensors, flow and tailpipe
tests for converters, etc. They seem to be 'shotgunning' the problem.

Carl

 

[Dano58]

Well, some folks have suggested that aftermarket O2 sensors are inferior
to OEM.

I think it's your shop's responsibilty to actually troubleshoot the
problem. There are oscilloscope tests for sensors, flow and tailpipe
tests for converters, etc. They seem to be 'shotgunning' the problem.

To say nothing of 'rifling' your checkbook!

I agree with Carl - most of the time, people walk into a repair shop
and say 'I have a CEL, please fix it'. It's the shop's responsibility
to diagnose the problem, fix it and bill you. Not throw some parts at
the problem, bill you, throw some more parts at the problem, bill you,
repeat.... Are they a Subaru specialist or a generic repair shop?

Dan D
'99 Impreza 2.5 RS (son's)
Central NJ USA