I saw this numerous times around here and figured MANY would like to know. It IS tricky. A while ago, after trying many combinations, I figured it out! I'm an old pro at this now, works every time. I pulled codes off another guy's '04 that never could get it either. Pay attention.

Jump in your truck, CLOSE DOOR.

Turn key ON

Turn key OFF

Turn key ON

Turn key OFF (Now here's where is gets tricky)

PUSH mileage button IN, AT THE SAME TIME you turn key ON again the third time. AS SOON AS KEY IS ON you must SIMOTANIOUSLY let go of mileage dash button and leave key in ON position

There you have it. This DOES NOT work if you hold the button in for all three strokes. AND you have to do this FAST.

Tell me how it works for ya

Again...

turn key on
turn key off
turn key on
turn key off
push button in AND turn key on
let go of button

it works to give you the c-codes for the dash. put didn't get the p- codes. never have been able to get the p-codes on the 04, worked on the 03.