P0420 - Catalyst System Efficiency Below Threshold (Bank 1)
Plain-English meaning
The vehicle's engine control module (ECM) has detected that the catalytic converter on bank 1 is not working as efficiently as expected.
What to check first
Array
What not to replace yet
Array
Stop driving when
No immediate need to stop driving; however, prolonged driving with this code may lead to increased emissions and potential damage to the catalytic converter.
Related symptoms
Array
Owner steps
Array
Likely causes
Faulty or degraded catalytic converter (medium)
Oxygen sensor malfunction (upstream or downstream) (medium)
Exhaust leaks before or near the oxygen sensors (medium)
Engine misfires causing unburned fuel to damage the catalyst (medium)
Wiring or connector issues related to oxygen sensors (medium)
Use of incorrect or contaminated fuel (medium)
Shop steps
Array
Follow-up questions
Has the vehicle failed an emissions test recently?
Are there any noticeable changes in fuel economy or engine performance?
Has any recent work been done on the exhaust or engine systems?
Are there any other diagnostic trouble codes present?