A vehicle will show a check-engine light or go into limp mode when the throttle sensor is unplugged before the ECU has had enough time to go to “sleep.” Since it thinks something has been unplugged, it shows you a light as a warning, even if you’ve already plugged it back in.
You can get rid of the check-engine light and cut out limp mode by removing the negative battery on your vehicle for 20 minutes, or by taking away the codes with an OBDII code reader, available at most stores.