Taken from WKJeeps:

"Retrieving codes (2005-2010 Grand Cherokee):

Insert and turn the ignition key from "Off" to "On" three times, moderately fast and without pausing ("ON" is when the digital odometer displays):

Tip: use the "count to 5" method, where "1" is the first "On":

Off > On > Off > On > Off > On
0 1 2 3 4 5

0 - Insert key (Off)
1 - On
2 - Off
3 - On
4 - Off
5 - On

At the third "On" the odometer display will read "DTC REPORT" and list the codes. If no codes are present the message "Done" will appear."

 

I must be stupid. I can't get it to display anything when I do that. Plug a friggin Predator into it. Lol

 

I tried it once when I had a CEL and it never worked for me either...

 

doesnt work for me either. hmm.. all i got was system ok.

 

Well, I think SYSTEM OK is the same as DONE.

 

take it to the dealer...you have a warranty

 

x2. Just get it checked out Davy.

 

Yeah just take it in. I got a full blown warranty for 70k miles so i take it in at drop of a hat. Cost chrysler 400 for the last time it went in there for a bad transfer case control module and final drive control module. My cost is 0. I don't care anymore i just take it in and ask for my free rental.