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Mazda
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2003
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MX-5 Miata Base, Standard
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Repair and Diagnosis
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Engine Performance
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System
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Engine Controls - Self-Diagnostics
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Diagnostic Tests
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DTC P0420: Catalyst System Efficiency Below Threshold
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Possible Causes
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Possible Causes
Three Way Catalytic (TWC) converter deterioration or malfunction.
Exhaust system leak.
Loose front HO2S.
Loose rear HO2S.
Front HO2S malfunction.