Can I Do A Smog Check If The Check Engine Light Is On?

In California, if the check engine light is on, your car will not pass the smog check. That’s because the 2017 BAR Smog Check manual states that checking the “Malfunction Indicator Light” (MIL) is a standard part of the functional test. The technician will first validate that the MIL is illuminated in the “key on engine off” position, and then start the engine. The MIL should, after a brief time of illumination, not be on on the “key on engine running” position. If the MIL (check engine light) is illuminated or flashes, this is a fail criteria. Note that it is also a fail criteria if the MIL does not illuminate at all. In other words, if the check engine light doesn’t turn on in the key on engine off position, that’s a fail, too.

What Should I Do If The Check Engine Light Is On Before A Smog Check?

So what should you do if your check engine light is on and you need to do a smog check? First, that depends if you already have resolved an issue with your car, and just need to clear the check engine light, or if the issue needs to be diagnosed.

If You Have Resolved The Issue, And Need To Clear The Check Engine Light Before Your Smog Test…

You have a few options to clear the MIL (check engine light) if it was not cleared by your mechanic or during the time of repair:

  • Drive the car around in mixed driving scenarios (freeway and street) for 2-3 days. It is possible this will clear the check engine light.
  • Stop and start the car 3 times (you can do this in quick succession).
  • Disconnect the car battery for 15 minutes (and try to actively drain the battery). Reconnect the car battery and the OBDII data will be cleared. Note that this will require you to complete an OBD Drive Cycle again before you can do a smog test, because all of your driving data will be erase.
  • Use an OBDII reader to erase the code.

If You Need To Diagnose the Check Engine Light…

  • If you have an OBDII reader, you can connect it to the OBD port and read the code.
  • You can visit an auto repair shop (like Autozone or O’Reilly Auto Parts) and ask the salesperson to give you the meaning of a diagnostic code.
  • You can simply go to a mechanic’s shop and ask them to diagnose and ultimately repair the code.

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