The AEV ProCal Module is must-have piece of equipment for the serious jeep owner. it's a simple and affordable way to program variations that aren't offered by the Jeep dealer or other re-programmers. Correct your speedometer and gear ratio for larger tires to increase transmission and engine performance, recalibrate your Tire Pressure Monitoring System, activate daytime running lamps, “one-touch” turn signals, increase idle speed for winch use, clear engine trouble codes, and more! The ProCal Module offers a series of easy-to-use DIP switches. Easy reference guide allows users to quickly program codes and plug the Module into the vehicle's OBDII to activate the new settings. The process merely takes minutes and can be reversed back to its original settings just as quickly. NOTICE: The AEV ProCal enables axle gear ratio changes for Wranglers equipped with the A580 Automatic transmission (2011+ 2.8L, 2012+ 3.6L) It CANNOT change axle gear ratios for 2011+ 2.8L CRD diesel Wranglers using a manual transmission. See more in the FAQ.