How to Clear OBD2 Codes (and Why the Check Engine Light Comes Back)

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You can clear OBD2 trouble codes with almost any scanner, but clearing a code does not fix the problem behind it. If the fault is still there, the check engine light will come back. Here is how it works and what to keep in mind.

How to Clear Codes

  • Plug the scanner into the OBD port and turn the ignition on.
  • Connect the scanner (if it is a Bluetooth model, connect it in the app).
  • Read and write down the codes first. You will lose them once cleared.
  • Choose the “erase codes” or “clear DTCs” option and confirm.
  • Turn the ignition off, then start the car and check whether the light stays off.

Why the Light Comes Back

The code exists because the computer detected a fault. If you have not fixed the cause (a loose gas cap, a failing sensor, a misfire), it will detect it again and the light will return, sometimes within minutes and sometimes after days.

Clearing Codes Resets the Readiness Monitors

Clearing codes also resets the car’s self-test “readiness monitors”. Emissions tests in many places require these to be complete, which can take a period of normal driving. Do not clear codes right before a test.

Permanent Codes

Some codes are stored as permanent and can only clear themselves after the car confirms the fault is gone. A scanner will not erase them.

Fix First, Clear Second

Look up what the code means before you clear it. My guide to common OBD2 error codes is a good place to start. If your scanner will not connect, see my 9 fixes for a scanner that won’t connect, and if you need one, see my OBD2 scanner guide.