It stopped working from the 2005 KJs I believe.
XRench3 can try it on his 2005 KJ.
Without starting the engine, rapidly turn the ignition ON/OFF 3 times.
After the last ON action leave the ignition ON and the Odometer display will show stored codes from the oldest to the latest.
You cannot erase codes using the KEY method but the last few codes can be investigated...the first codes to roll out could be ancient and no longer valid.
The Export Models such as I have seem to need 4 ON/OFF actions...I will check to see if 3 actions work on my 2002 Export CRD!
My Jeep uses only PCI Bus and even the local Bosch agents cannot pull codes or erase codes...only the Dealers with their DBIII readers can do so.
You guys with newer Jeeps should find a code reader that works on your Jeep and make use of it!
Yesterday my Jeep "Pinged" at me and died. I pulled out my Laptop which I always carry with me...pulled the last codes using the KEY method which pointed to the Oil Pressure Sensor according to the codes I have stored on my Laptop along with the 2002 Service Manuals, Tools, a big hat and a Multi-meter.
I topped up with oil...which I always carry with me and Jeep seems OK!
This old girl KJ of mine does burn oil and leaks a bit....fortunately the Owner does not leak yet!