What kind of car? If it is a GM you can read the code with a paper clip. You just find the plugin under the dash and place one end into the right upper corner and the other end into the slot nest to that one. Turn the key on and count the flashes of the engine light. It will flash, for example, two fast flashes a pause then three more fast flashes, for 23. It will repeat this 3 times then give you another number. It will do this till there is no more codes and then start over again.
Hope this helps. If it is a Ford product, good luck. They want you to have to bring it back to the dealer for repairs. Look at how you have to get the codes even with a scannar. Turn wheel to left, center the wheel, step on the breaks, and so on and so on then all you get is codes.