Diagnosis Guide · Reviewed Oct 3, 2026
How to Reset Your Check Engine Light (and Avoid Failing Emissions)
You can turn a check engine light off, but it will come back if the fault is still there. Here is the right order: read the code, fix the cause, clear the code, then finish a drive cycle before any emissions test.
By Alan Williams, independent AMSOIL Dealer since 2004, Tomball, TX
How do you reset a check engine light?
Fix the problem first. Then clear the code with an OBD2 scanner, or let the light go out on its own after the repair and a few drive cycles.
A flashing check engine light means stop driving and get it checked, because it often signals a misfire that can damage the catalytic converter.
The right order: read, repair, clear
- Read the code with an OBD2 scanner or at a parts store. Write it down.
- Check the simple causes first, such as a loose gas cap (tighten until it clicks).
- Repair the fault.
- Clear the code with the scanner.
- Drive normally so the car can re-run its self-tests.
If the light returns, the problem is not fixed. Our guide to dashboard warning lights explains which lights are urgent.
Ways to reset the light
| Method | How | Caution |
|---|---|---|
| OBD2 scanner | Plug in, select “Clear codes” | Best method. Read the code and freeze data first. |
| Fix it and wait | The light can clear itself after several clean drive cycles | Slow, but it keeps readiness history. |
| Disconnect the battery | Disconnect the negative cable for several minutes | Last resort. It erases radio and learned settings, and resets readiness monitors. |
Keep your engine healthy between warning lights. Preferred Customers save about 25% on AMSOIL oil and filters.
Why resetting can make you fail an emissions test
Your car runs self-tests called readiness monitors. Clearing codes or disconnecting the battery sets them to “Not Ready,” and many inspections reject cars with incomplete monitors. The Texas Department of Public Safety explains that clearing codes or a battery disconnect resets monitors, and driving a drive cycle sets them back to Ready.
- Do not clear codes right before an inspection.
- Drive normally for days, including highway and city driving, until monitors complete.
- Some stored “permanent” codes cannot be erased by a scanner or battery disconnect.
When not to reset at all
If the light is flashing, the engine runs rough, or the temperature or oil light is on, stop and have it inspected. For unusual sounds, see engine noises and what they mean.
Check engine light FAQ
Will the check engine light reset itself?
Yes, after the problem is fixed and the car completes several drive cycles, but it may take days.
Does disconnecting the battery reset the check engine light?
It can, but it also erases readiness monitors and settings, and the light returns if the fault remains.
How long do readiness monitors take to reset?
It varies by vehicle. Several days of mixed driving is typical, and some need a specific drive cycle.
Can I pass an emissions test right after clearing codes?
Usually not, because monitors will show Not Ready.
What does a flashing check engine light mean?
A more urgent problem, often a misfire. Reduce load and get the car checked.
Maintain your engine for less
AMSOIL Preferred Customer membership is $20/year (or a $10 six-month trial), with free shipping on orders of $100 or more.
Sources (checked Oct 3, 2026): Texas DPS: readiness monitors (Ready or Not) · Redline Car Garage: clearing OBD2 codes · Apex Auto: readiness monitors
AMSOIL is a registered trademark of AMSOIL INC. LubeOilSales.com is operated by Alan Williams, an independent AMSOIL Dealer (Dealer #1243776), and is not owned or endorsed by AMSOIL INC. If you join through my links, I may earn a commission at no extra cost to you. This guide is general information. Follow your owner’s manual and consult a qualified professional when in doubt. Content last reviewed October 3, 2026.