I own a 2000 Jeep Cherokee Sport (6 cyclinder - 53,000 miles) and I'm getting an OBD-II reading of Cylinder Misfire from a Portable OBD-II scanner. The place I rented the scanner said that Chrysler codes are some times not readable from OBD-II scanners and that I would need to take this a dealer, is this true? If not can anyone recommend a handheld scanner that one could purchase to scan the OBD-II sensors and reset the Check Engine light that isn't to expensive.

Second, the parts store I rented the OBD-II scanner suggested running a higher octane gas to correct the Cylinder Misfire. Currently I run an 87 octane, will a 90 octane or higher fix this or should I look at replacing spark plugs, wire, etc..?

All chrysler products have a built in scanner, the way to use it is to flip the ignition back and forth 4 times, the check engine light should come on for a moment and then start to blink.  The way that you can tell the codes that it is throwing is by watching for the # of times it blinks in between pauses. All codes are 2 #s long, the first code it will always through is the electricle code and the last code will always through is the finish code.  Any code in between the first and last should be writen down.  Then all you have to do is call up autozone and they will tell you what the codes mean.  If you actually go to autozone then they can do it for you, just ask them to do a diognostic test for you and they will even print out the troubleshooting sheets that tell you all of the possible problems and fixes to the problems when that code is throwen.  And the gas could be a possibility, my chrysler lebaron will barily run off of 87 octane and only runs well off of 91 or higher.