To reset the check-engine light in vehicles manufactured in and after 1996, use an OBD II code-scanning tool to clear the codes stored in the control module. Another option to reset the check-engine light is to disconnect the battery, and drain the power from the control module. Use caution when disconnecting the battery to clear the check-engine light, as this can delete important information.
To use an OBD II code scanner, connect the device to the OBD II connection port, which is typically located near the steering column inside the car. Write down the diagnostic codes that appear, and press the Clear Codes button on the code-scanning device to turn off the check-engine light.
To turn off the check-engine light in cars built prior to 1996, disconnect the battery terminals for at least 10 seconds, and reconnect the battery. In vehicles built after 1996, disconnect the battery terminals, and hold down the horn button for at least 30 seconds to drain the stored power in the control module.
Some problems, such as unusual engine idling, can occur after disconnecting the battery. Drive the vehicle at highway speeds to correct the problems. See a mechanic if the problems persist, or if the check-engine light turns on after resetting it.