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catalyst system efficiency below threshold

  1. Attempting to Use Overformatted Data to Fix P0420

    Gen 3: 2005-2009
    Hi friends, I recently had my first run-in with the infamous P0420 code (Catalyst System Efficiency Below Threshold) on my 2006 Outback 2.5 Limited. The CEL has been on with the P0420 code for probably about a month now. At first, it was intermittent and would sometimes go off on its own (I...