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p0420
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  1. EJ25 - 2.5L Non-Turbo (1998-2010)
    I’ve been having some issues with my 2009 Forester….165k miles. Threw codes for misfire cylinders 2 & 3 and the P0420. Replaced plug wires, coil pack, and spark plugs. Found oil on the plugs and a small leak around the valve cover so I have new gaskets/and tube seals on the way. In the...
  2. EJ25 - 2.5L Non-Turbo (1998-2010)
    Hello! I've perused the forums looking for a solution and I've came up short. I also have very little working knowledge of repairs and advanced car repairs. My 09 Forester has around 130k on it and over the past few weeks I've had some issues with a P0420 code. I have a persistent code reader...
  3. Engine Management, Tuning and Datalogging
    Hi all! Yesterday I was finally able to read my ecu by selecting 2007+ from the list. Previously was hitting my head into sti05 and it always failed. Well anyways, I found out that in the ecu in diagnostics codes the CAT EFFICIENCY BELOW THRESHOLD was disabled, with numerous...
  4. FA20DIT - 2.0L Direct-Injection/Turbo (2014-2018)
    I had the p0420 code come on about a week ago saying Catalytic converter system bank 1 below threshold. I started experiencing some sort of hesitation/studder feeling when driving on the interstate a couple days ago. It only happens when at highway speeds (65-75). I haven’t had the time to take...
  5. General Troubleshooting and Technical Help
    I replaced the OEM exhaust manifold in my 2009 Forester with an Eastern Catalytic Manifold from Rock Auto. Had the install verified by my mechanic. After about 200 miles the P420 code came back on. Mechanic states that the rear O2 sensor reads all over the place while running, 100mV - 1000mV...
  6. General Troubleshooting and Technical Help
    I have a 2009 Forester X that's showing p0420 and have been trying the other fixes to delay replacing the Catalytic Converter until I have money to do so. I have no performance issues right now. Does anybody have experience using an o2 sensor spacer for the rear o2 sensor? What size are the...
  7. General Troubleshooting and Technical Help
    Hey guys, Started having issues months ago when my 2010 Subaru Forester (133K miles) threw the P2096 code. I started replacing things one at a time, solving the P2096 code, but now I have the P0420 that keeps coming back. Since the beginning I've had intermittent issues with cold starts and the...
  8. General Troubleshooting and Technical Help
    Question for anyone who might have some advice: I love Foresters...now on my second one, an '07 2.5X. It's a manual and it's been really good to me these past few years... BUT, it's needed work recently and now I need help. There was a P0420 code that kept coming back, so my mechanic put in a...
  9. General Troubleshooting and Technical Help
    Hi my high mileage (443K km) Forester has been throwing a check engine code for a while now. Got it read and it was P0420 - Catalyst System Efficiency below Threshold, Bank 1. My mechanic just called and 1) noted the head gasket leak is much worse than previous); 2) cylinder 3 is misfiring; and...
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