I to have tried to retrieve MIL codes using the key on off 3 times method and I have not been able to get it to work! I have an 08 quad cab 4x4.

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08 2500 Quad Cab, Big Horn, Auto.,Volant CAI with Powercore, Auto Meter Boost, Pyro., and Trans Temp., Muffler Delete, 03 Crossroads Cruiser 30' 5th wheel.