this is caused by the sensor tripping in the light sensor to see what causes this you must diagnose it with a computer and see what fails in it.
You may think there is nothing wrong but there is. If the check engine light is on there will be codes stored in the ECM. Have the codes read. The codes will help you determine what the cause is.
If not installed properly check engine light will illuminate
Check
check
there could be a thousand different reasons. there is no way to tell or even guess with the iformation you have given.
in neutral while engine warm and running. be sure to have emergency braake on.
http://www.scribd.com/doc/6382741/Mitsubishi-Galant-2003-Systeme-de-Chauffage-Et-Climatisation- check section 50-40 AlexR
Mitsubishi gallant is both automatic and standard. You can check out some car classifieds on the net to see the different transmission.
Check your coils on the sparkplugs
It will be an icon of an engine or it will just say Check Engine.
To install a freeze plug on a 2003 Mitsubishi Galant, first drain the engine coolant and clean the area around the freeze plug hole. Apply a thin layer of sealant to the edges of the new freeze plug, then use a socket or a similar tool to tap it gently into place, ensuring it sits flush with the engine block. Finally, refill the coolant and check for leaks before starting the engine.
You cannot reset a code. Take out your radio. Check the serial number on it and call Mitsubishi dealer. They will check a database and give you a code.