Catalog

OBD-II codes

Look up a code your scanner returned. Each entry covers the generic meaning, the system it points to, the common causes, and the order to check them in.

P0420 Code: Catalyst System Efficiency Below Threshold — Causes, Diagnosis, and Fixes
P0420 means the catalytic converter is not cleaning exhaust gases efficiently. Causes range from a $100 O2 sensor to a $2,000 catalyst replacement — here's how to tell which fix you need.

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