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Home >> Subaru >> 2001 >> Outback Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics - 3.0L >> Diagnostic Tests >> DTC P0420: Catalyst System Efficiency Below Threshold

DTC P0420: Catalyst System Efficiency Below Threshold

  1. Perform basic diagnostic procedure. See BASIC DIAGNOSTIC PROCEDURE  . If DTC P0420 is only DTC set, go to next step. If DTCs P0031, P0032, P0037, P0038, P0051, P0052, P0131, P0132, P0133, P0136, P0139, P0151, P0152, P0153, P0301, P0302, P0303, P0304, P0305, P0306, P1134, P1139 and/or P1140 are present, diagnose and repair those DTCs. Do not diagnose DTC P0420.
  2. Check for exhaust leaks or air suction caused by loose or missing nuts and bolts, or damage to exhaust system. Check especially between cylinder head and front exhaust pipe, between front exhaust pipe and front catalytic converter, and between front and rear catalytic converters. If damage is found, repair or replace exhaust system. If no damage is found, go to next step.
  3. Separate rear catalytic converter from exhaust pipe. If there is damage at rear face of rear catalytic converter, replace front and rear catalytic converters. If there is no damage to rear catalytic converter, remove front catalytic converter. If there is damage to front or rear face of front catalytic converter, replace front catalytic converter. If there is no damage to front catalytic converter, contact authorized Subaru dealership because probable cause is deterioration of multiple parts. Clear memory and perform verification procedure. See CLEARING DIAGNOSTIC TROUBLE CODES  and VERIFICATION PROCEDURE  .
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