Drive with caution — fix soon.
P0420 means the computer compared the two oxygen sensors around your catalytic converter and decided the converter isn't reducing pollution efficiently enough. It doesn't always mean the converter is dead; a faulty sensor, an exhaust leak, or a separate engine problem can fool the system. A proper diagnosis checks the sensors and exhaust before condemning the expensive converter.
$200 – $2200
Varies by vehicle and root cause.
Yes, short-term driving is generally safe and the car runs normally. You'll fail emissions and could lose a little fuel economy, so get it checked within a few weeks before it worsens.
It ranges widely: an oxygen sensor or exhaust leak repair can be $200-$500, while replacing the catalytic converter often runs $900-$2,200 depending on the vehicle and whether you use OEM parts.
It's moderate. It won't strand you, but it signals reduced emissions performance and can lead to a costly converter replacement if an underlying issue like a misfire is ignored.
No. Many P0420 cases are caused by a bad oxygen sensor, an exhaust leak, or another engine fault. A technician should verify the converter is actually failing before replacing it.