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Check out the Super duty Forum.The second thread has 2 pages of specs explaining all of the factory codes.My sticker was below the door striker pin on the drivers side.
Three ways...1) check the code under AX on the data plate on the LH door jamb, 2) crawl under the truck and look at the tag bolted to the rear diff cover. Your axle ratio is located at the lower left corner of the tag. If the ratio says 3.73 or 4.30, then the diff is open; if it says 3L73 or 4L30, it's Traction-Lok. 3) jack the truck up by the rear diff, put the tranny in neutral, and turn one tire by hand. If the opposite tire turns in the same direction, it's Traction-Lok...if it turns the other direction, it's an open diff.
