10/13/2026
New gas cap and that check engine light is STILL on? 🐗 Easy, bud. Here's what's going on:
• A loose or bad gas cap can set an EVAP leak code (usually something like P0455 or P0457).
• Fixing the cap won't shut the light off right away. Your car's computer has to re-run its EVAP self-test over several drive cycles, so give it a few days of normal driving.
• Don't guess. Get the code read. A cheap OBD2 reader works, and lots of parts stores will read it for free.
• If the light comes back, it may be something else in the EVAP system, like a purge valve, a vent valve or a cracked hose. Get it checked.
• And if that light is ever FLASHING, that's not a gas cap problem. Get it looked at right away.
Ever had a gas cap turn on your check engine light? Tell us in the comments 👇
This is Behind the Ham, our behind-the-scenes series from Farmington, AR. More on the Dirty Ham's Garage YouTube channel. (Voiceover by Dave, our AI narrator.)