Should I worry about the check engine light P0420 on my Honda Civic?

[Emily.W]

My 2017 Civic’s check engine light came on yesterday and the code reader says it’s P0420. The car seems to drive completely normally, no weird sounds or loss of power, which has me a bit confused. I’m just wondering if this is something that needs immediate attention or if I have a little time to figure it out.

[ZoeyNB]

P0420 is a catalyst efficiency code. It doesn’t always mean the converter is dead; sensor glitches or a small leak can trigger it.

[GregoryL]

If the car still runs normally and the light isn’t flashing, you probably have a little time, but it isn’t something to ignore for too long.

[FrankBP]

I’d start with the easy checks: make sure the gas cap is tight, and look for obvious exhaust leaks or damaged wiring around the O2 sensors. If nothing obvious shows, take it in for a read and see if it returns after a few drives.

[Addison_W]

One time I got that code and the problem turned out to be a loose harness on a downstream O2 sensor; I reseated it and the code didn’t come back for a while.

[AdamSM]

If the light starts blinking, stop driving and get it checked—that’s usually a sign of a misfire and possible catalyst damage risk.

[Layla_S]

Want help mapping out the next steps or just vent about how vague these codes can feel?