Hello everyone, here's the history of the current problem. Bought a used 2003 Subaru Legacy with 190K miles. after 1 month P0420 cat efficiency code tripped the engine light. The light seems to come and go with no repair work done. 2 months later the car hesitates severely upon acceleration but does finally get going. I am not limited to any certain speed on the highway yet. Exhaust shop said cats were fine after they cut a hole and actually visualized the inside of the cat. Then I took it to firestone who said it WAS the CC. There was no diagnostic work done as admitted by firestone once they say that the P0420 code had been stored in the "computer". Was quoted 1200 to replace CC and 1100 to replace the O2 sensors. Should I believe the exhaust shop or Firestone? Can I replace the CC myself?

Asked by Jul 15, 2017 at 04:35 PM about the 2003 Subaru Legacy 2.5 L

Question type: Maintenance & Repair

Paid 2300.00 for the car for my 16y.o. daughter.  Only seems to have severe
problems once engine gets warm.

2 Answers


$1100 to replace O2 sensors? No way. Doing exhaust work requires a torch and some welding, because the old stuff will be rusty. O2's should be $50 a piece and labor to install. You have a couple. Find an independent shop that can properly diagnose your problem, and have the repair completed for much less than the Firestone quotes.......https://www.obd-codes.com/p0420


Wonder why I didn't see this one.... PO420 codes for "cat conv insufficiency" are endemic in 2000-2009 2.5i...especially late 2004-2009 PZEV, as the ultra-tight operating range of the ECM doesn't accommodate temperature spikes inherent in richer winter-area fuels. SOA recalled a bunch for free cats, but that's old news. Just drive your car and erase the CEL before inspection time. Note that most cheap aftermarket cats will NOT solve the problem...only the $900+ ones. Clearly your antique should pass on this one....

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