🛡️ Catalytic Converter Codes
TL;DR
Catalyst codes (P0420 Bank 1, P0430 Bank 2) mean converter efficiency is below threshold. Severity: medium. You can usually drive short-term but will fail emissions. Causes: a worn catalytic converter (~55%), a bad rear O2 sensor (~30%), or an exhaust leak (~10%). Diagnose before buying the expensive part.
Codes in this family
Shared causes
- Worn or failed catalytic converter
- Faulty downstream (rear) oxygen sensor
- Exhaust leak before or near the converter
- An upstream problem (misfire, rich mixture, oil burning) that damaged the converter
Parts commonly involved
Related symptoms
Frequently asked questions
Does P0420 always mean I need a new catalytic converter?
No. The converter is the cause about 55% of the time; a faulty rear oxygen sensor (~30%) or an exhaust leak (~10%) can also set P0420. Diagnose first before spending on the expensive part.
What is the difference between P0420 and P0430?
They are the same fault on different banks: P0420 is Bank 1 (the cylinder bank with cylinder 1), P0430 is Bank 2. On a four-cylinder engine you will only see P0420.
Will a cat cleaner fix a P0420?
Sometimes, if the converter is only mildly contaminated and the underlying cause is fixed. It is a cheap first try, but it cannot rebuild a converter that has physically failed.