GarageDex

How to Reset the Check Engine Light

Reviewed by GarageDex editorial

GarageDex's code reference shows the right order: read the code, fix the cause, then clear the light with an OBD-II scanner. Resetting the light without fixing the problem only hides it for a while. The computer re-tests the system, finds the same fault, and turns the light back on.

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Step by step with a scanner

  1. Park with the engine off and find the OBD-II port, usually under the dashboard near the steering column.
  2. Plug in an OBD-II scanner and turn the ignition to on without starting the engine.
  3. Read and write down every stored code before clearing anything - once cleared, the record is gone.
  4. Look the codes up and fix the underlying cause, such as tightening the gas cap or replacing a failed sensor.
  5. Use the scanner's clear or erase codes function to turn the light off.
  6. Drive normally over the next several days so the system can re-run its self-tests.
  7. If the light returns, read the code again - the fault was not fixed, or a related one remains.

Tools used in this guide

  • OBD-II scannerReads the stored code, then clears it once the repair is doneView on Amazon

These tools fit any vehicle. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you.

Read the code before you clear it

This is the step people skip, and it is the one that matters. The stored code is the only record of what went wrong. Write it down, then look it up in our trouble code reference for the meaning and likely fix. Many auto parts stores will read it for free if you do not own a scanner.

Why the light comes back

The engine computer runs a set of self-tests called readiness monitors. Clearing codes resets all of them to incomplete. As you drive, each test runs again. If the fault is still there, that test fails and the light returns, sometimes within one trip and sometimes after a few days, depending on which system failed.

The battery method, and its costs

Disconnecting the negative battery terminal clears the light on most cars, but it wipes more than the code. Expect to reset the clock and radio, and the engine may idle unevenly for a while as it relearns its settings. If you change the battery anyway, see how to replace a car battery.

Not sure it is safe to keep driving?

Check solid vs flashing first. A flashing light means an active misfire, and it should not be cleared and driven on.

Frequently asked

Does disconnecting the battery reset the check engine light?

On most cars, yes, after the battery has been disconnected long enough for the computer to lose power. It also erases the stored codes, radio presets, and learned idle and fuel trim settings, and it can trigger a security lockout on some audio units. A scanner clears the light without those side effects.

Will the check engine light reset itself?

Often, if the fault is fixed. The computer re-runs its tests during normal driving, and after several consecutive clean drive cycles it turns the light off. A gas cap fix typically clears this way.

Why did my check engine light come back after resetting it?

Because clearing a code does not repair anything. If the fault is still present, the next time the computer runs that test it fails again and relights the warning.

Can I reset the check engine light right before an emissions test?

It will not help. Clearing codes also resets the readiness monitors, and inspection stations check that those monitors have completed. A freshly cleared car usually fails as not ready until it has been driven for several days.

Need your car's exact spec?

Look up your trouble code