P0420Catalyst efficiency low
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Common codes, decoded
P0420
Catalyst efficiency below threshold
Oxygen sensor readings suggest the catalytic converter is underperforming.
P0300
Random or multiple misfire
Misfires detected across cylinders. Spark, fuel, and air are common suspects.
P0171
System too lean
More air or less fuel than expected. Vacuum leaks are a typical start.
P0442
Small EVAP leak
A small fuel vapor leak. A loose gas cap is a frequent cause.
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Three steps to clarity
Plug in
Connect a scanner to the OBD-II port under the dash.
Read the code
Note the five-character code it shows.
Walk in informed
Look it up here, then talk to a technician with confidence.
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