03's just cycle key off/on three times and let it stay in the on position and it will tell you if you have thrown any codes. Don't start the engine, at least that is how mine works. I did not have to hold down trip button.When looking for the codes after you do this it will say DONE. Look where your odometer/trip is displayed.

 

Sittenbull2 is right. Cycle the key 3 times to see if any codes are stored. Don't bother with the trip button. I have done this several times on mine when I was having trouble with the JTEC plug. Interesting...I had to show this method to my dealers mechanic!!!!