How to clear a check engine light and reset codes

Clearing a check engine light is easy — but doing it before you’ve fixed the underlying fault just hides the problem until the car re-detects it. Read and understand your code first (how to read OBD-II codes), repair the cause, then reset.

The right way: use a scanner

1. Plug the scanner into the OBD-II port and turn the key to “on.”
2. Read and record the codes first, so you know what you’re clearing.
3. Select “Erase / Clear codes.” The tool resets the stored codes and turns off the light.
4. Drive a few cycles. If the fault is truly fixed, the light stays off. If it returns, the problem isn’t solved.

This is the cleanest method and works on every OBD-II vehicle.

Will disconnecting the battery clear it?

It can, but it’s a blunt tool. Disconnecting the battery for several minutes may reset the computer and clear codes — but it also wipes learned fuel trims, radio presets, and other settings, and it won’t fix anything. A scanner is faster and safer.

Why the light comes back

If the code returns after a drive cycle or two, the underlying fault is still present. For example, a P0420 will keep returning until the converter or sensor issue is actually repaired, and a P0455 EVAP leak returns until the leak is sealed.

Important: emissions testing

Clearing codes also resets your car’s readiness monitors. Most emissions tests will fail a car whose monitors aren’t “ready,” so don’t clear codes right before a smog check — drive several normal cycles first to let the monitors reset.

Bottom line

Fix the cause, then clear the code to confirm the repair. If the light returns, look the code back up in our database and keep diagnosing.