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DTC P0420 (CAT) - CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD Subaru Outback BG

Testing & Diagnostics ~160 words
  1. Connect SSM. Turn ignition on. Retrieve DTC(s). If DTC P0130, P0133, P0135, P0136, P0139 or P0141 is present, diagnose affected DTC(s) first. Clear DTC(s) and retest. If no DTC is found, go to next step.
  2. Turn ignition off. Check for gas 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 converter. 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 converter, remove front catalytic converter. If there is damage to front or rear face of front catalytic converter, replace converter.

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