I always have trouble finding these diagnostic codes, so I'm putting them here as much for myself as anyone else that needs to see them. 

When I researched this topic, I have found some variances in the answers.  What I've posted here is those things that seem to be consistent or the majority of the sites I've reviewed have agreed on.  I have not tried these, so let me know if you have something different.
  My 95 Cherokee has an OBD-I system (that stands for On Board Diagnostics) which was used in the older jeep products.  After 1998, jeep began using the OBD-II system which is completely different and has a completely different list of diagnostic codes.

   To put the vehicle in the diagnostics mode, insert the key in the ignition then within 5 seconds turn the key to ON (not start) then OFF, then ON-OFF-ON.  (A couple of sites I saw stated an additional ON-OFF was needed, but I tried it and it worked both ways.)  When you turn the key to off, you don't need to turn all the way to the lock position.
It's a little hard to see in the picture, but the "CHECK ENGINE" light is in the second row from the bottom on the left side.

   After you do the ON-OFF-ON-OFF-ON sequence, the check engine light will come on for a few seconds then shut off.  Then you have to wait for it to start flashing.  Mine took about 5 seconds to start.  It will then begin flashing the error codes, that is, it will flash once for 1, twice for 2, etc.  I was afraid it would flash the numbers too fast, but it didn't, and there's a long pause between each number (enough time to write down the number you read).  When all the codes have been read, the system will flash 55.