• Tiny
  • legacy98
  • 1998 Subaru Outback

1998 Subaru Outback All Wheel Drive Automatic 152500 miles

Hey there -

So my check engine light came on about a week ago so I hooked it up to my diagnostic scanner and the code " P0420 Catalyst System Efficiency Below Threshold (Bank 1)" popped up. It's just confusing because with every code, there could be are multiple possiblities of what the problem should be. I was wondering if you might be able to help me narrow down my search. I just bought this 1998 Subaru Outback about a month ago, and it has been driving a little bumpy and shudders occasionally (usually when it's shifting from 1st or 2nd gear). Any suggestions?


Friday, March 20th, 2009 AT 6:43 AM

1 Answer

  • Tiny
  • rasmataz
  • Member

Might not be the Cat could be other things involves here

Why did the converter go bad? Under normal use, converters are engineered to last upwards of 150,000 miles. But any number of things can make it fail prematurely. The most common cause is contamination of the catalyst because the engine is burning oil or leaking coolant internally (leaky head gasket or a crack in a combustion chamber or cylinder). Converters can also be damaged if they overheat due to ignition misfiring that allows unburned fuel to pass through into the exhaust (check for a fouled spark plug or bad plug wire). The same thing can happen if the engine has a bad exhaust valve that leaks compression into the exhaust (check compression). Bad oxygen sensors

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Friday, March 20th, 2009 AT 7:15 AM

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