there should be a procedure you can do without a reader. For a jeep im thinking pull the pcm fuse, turn and hold the key to clear it. You can also get the code from the odometer on obd2 but there are some years that it doesn't work.
I'd still buy a reader. I got one of those things to plug into the obd2 port and plug in the laptop. You can clear codes and also get some live data from certain systems. They also have bluetooth/app versions.