Can I clear OBD-II codes myself?
How to clear codes
The easiest way is with an OBD-II scanner: plug it in, turn the ignition on, and select 'Clear Codes' or 'Erase Codes' from the menu. This tells the engine computer to wipe stored codes and freeze frame data. You can also disconnect the negative battery cable for about 15 minutes, but that resets all learned settings, radio presets, and may require a relearn procedure for idle or transmission.
After clearing, the codes may come back immediately if the fault is still present. If they don't, the issue might have been intermittent. However, clearing codes also resets emissions readiness monitors, which means you can't pass an emissions test until the car completes a drive cycle—often 50-100 miles of mixed driving.
- Use a scanner's 'Clear Codes' function—it's quick and safe.
- Disconnecting the battery works but resets other settings.
- Codes return if the problem isn't fixed.
- Clearing resets emissions readiness; you'll need to drive to reset.
- Never clear codes right before an emissions test.
- Write down codes before clearing so you have a record.
When to clear and when to diagnose
Clearing codes is fine after you've repaired a problem—it turns off the check engine light and lets you verify the fix. But clearing codes to 'make the light go away' without diagnosing is a bad idea. You'll lose freeze frame data that helps pinpoint the issue, and the code will likely return. In some states, clearing codes just before an emissions test will cause a 'not ready' result and fail you.
If you're not sure what a code means, write it down and look it up before clearing. Use the code as a starting point for diagnosis. If you're not comfortable diagnosing, a mechanic can read and interpret codes for a diagnostic fee, often $50-$150, which may be applied to repairs.
Common mistakes
- Clearing codes to turn off the light without fixing the problem—it will come back.
- Disconnecting the battery and losing radio settings and idle relearn.
- Clearing codes right before an emissions test, causing a 'not ready' failure.
