malfunction indicator light goes on

Absolutely has to be SCANNED for code / codes that turned it on.... Some Auto Parts stores will do that for FREE hoping you will buy the necessary parts from them. ADVANCE AUTO STORES and AUTOZONE are two examples. Do that and take the code home with you (take their advice and thank them) and then 'google' the code with your make/model and that should give you an idea where to Start !! If you are not technical or are mechanically challenged then it's time to take it to your repair shop