In addition to other people's recommendations, your car may have a way of spitting out the code to you. Go look on the internet for 'read OBD codes <car model>

In addition to other people's recommendations, your car may have a way of spitting out the code to you. Go look on the internet for 'read OBD codes <car model>'. It might be as easy as turning the car on/off/on/off/on in less than 10 seconds and reading the digital odometer, or as complicated as a 10-step process that spits out the codes to you as a number of flashes of the dashboard display. That said, having an OBD reader could make you everyone's new best friend.