98 Legacy OBD2 code P0420

[Guest]

The car has 150,000 Km's (90,000 miles?). It has been flawless, until
the MIL - P0420. Subaru dealer wanted to play "Replace parts til he's
broke" I have changed the rear O2 sensor, now have a new catalytic
converter. I do not wish to just keep throwing parts at it. I thought
that a Subaru dealer should have the equipment to look at the ECM inputs
and O2 outputs, etc...
HELP... if anyone has experienced this or something like it, I would
appreciate any help. Where do I go from here, BROKE ??

 

[TG]

What does that code mean? TG

 

[TG]

OK, low catalyst efficiency. Usually replacing the exhaust manifold gaskets
will cure this. I like to replace or at least chase the studs, you need an
accurate torque reading here. Check for any other exhaust leaks upstream of
the O2 sensors. TG