hc2020 Posted June 5, 2012 Share Posted June 5, 2012 I have an '04 Subaru legacy, naturally aspirated, 2.5l. The car is displaying extreme hesitation when you first press on the gas and anytime from 30-40 mph. I ran my diagnostic tool and received three messages: PO301 - Cylinder 1 misfire detected, PO304 - Cylinder 4 misfire detected, & P0420 - Catalyst system efficiency below threshold. I was wondering if anyone had some suggestions. I am unsure if I need to replace the catalytic converter, the air assist injector solenoid, the idle air control solenoid valve, or something different. Any advice would be appreciated. Thanks and have a great day! Link to comment Share on other sites More sharing options...
No DRFT Posted June 5, 2012 Share Posted June 5, 2012 Po420 is related to the exhaust system. Probably a o2 sensor or clogged cat. I have no control over drippie. Link to comment Share on other sites More sharing options...
WhiskeyTango Posted June 5, 2012 Share Posted June 5, 2012 I like how the 0420 code is related to smoke Link to comment Share on other sites More sharing options...
boostedgrocerygetter Posted June 5, 2012 Share Posted June 5, 2012 id say you probably have a faulty cat which in turn could have caused your misfire if the cat is semi clogged. i would solve the cat issue first. that or the o2 could be reading wrong due to your cat or sensor making the car run rich or lean and burned up a valve or fouled the plugs. could be a number of issues. Link to comment Share on other sites More sharing options...
mwiener2 Posted June 5, 2012 Share Posted June 5, 2012 Headgaskets!!$!11!?!1! My Mods List (Updated 8/22/17) 2005 Outback FMT Running on Electrons Link to comment Share on other sites More sharing options...
FJuan Posted June 5, 2012 Share Posted June 5, 2012 id say you probably have a faulty cat which in turn could have caused your misfire if the cat is semi clogged. i would solve the cat issue first. that or the o2 could be reading wrong due to your cat or sensor making the car run rich or lean and burned up a valve or fouled the plugs. could be a number of issues. ^^ This Just to add, had the same issue in my BMW and after testing all the O2 sensors, it turned out to be one of the Cats was defective. After replacing the Cats the car ran normal again, and corrected the misfire codes as well. Test your O2 sensor first, since this is fairly easy and cheap to do. If you don't know how to test, search YouTube for "How to test 02 sensors". My wife's balls are delicious. Link to comment Share on other sites More sharing options...
mnstrmech Posted June 5, 2012 Share Posted June 5, 2012 p0420 is ALWAYS a dead cat code.... plain and simple... and starting to clog up... gotta get it replaced asap... Link to comment Share on other sites More sharing options...
hc2020 Posted June 6, 2012 Author Share Posted June 6, 2012 Thank you for all the helpful information. Link to comment Share on other sites More sharing options...
BlackWagon GT Posted June 9, 2012 Share Posted June 9, 2012 p0420 is ALWAYS a dead cat code.... plain and simple... and starting to clog up... gotta get it replaced asap... 99% of the time, your statement is correct, including the OP's case. However, when my car had that code (completely stock exhaust) it was due to an exhaust leak that allowed air entry into the exhaust stream because some hack didn't fully tighten down the joint bolts. Link to comment Share on other sites More sharing options...
RuskiTrombone Posted June 9, 2012 Share Posted June 9, 2012 Spark plug defouler should do the trick Link to comment Share on other sites More sharing options...
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