Turn off a malfunction indicator light, commonly called a check engine light, by rectifying the issue triggering the on-board diagnostic system to activate the light. Determine the cause of malfunction indicator light activation, or turn the indicator light off, by using an OBD II trouble code scan tool or taking the vehicle to an automotive repair technician.
Some models of car reset the malfunction indicator light when the battery is disconnected for a period of time and then reconnected. Perform the battery disconnect procedure by disconnecting the negative cable from the battery terminal for 5 minutes. During this time, switch the ignition to the on position three times and return the ignition to the off position. Reconnect the negative cable to the negative battery terminal. Turn the ignition to the on position and start the automobile after 1 minute, and the malfunction indicator light should be turned off.
Late model vehicles, especially those manufactured prior to 1996, may not reset the malfunction indicator light after the battery disconnect procedure due to the electronic control module storing the trouble code information in its ROM. Such a vehicle requires a trouble code scan tool to reset the indicator light. Never drive a vehicle for extended periods of time with a lit malfunction indicator light to prevent engine damage or further malfunctions. When the malfunction indicator light is flashing, cease operation of the vehicle and bring it to an automotive repair specialist before resuming use.