2007 Dodge Ram 1500 Pickup Owner's Manual - Page 324

324 STARTING AND OPERATING The "SERVICE 4WD" warning light monitors the electric shift 4WD system. If this light remains on after engine start up or illuminates during driving, it means that the 4WD system is not functioning properly and that service is required. When operating your vehicle in 4WD LO, the engine speed is approximately three times that of the 2WD, 4WD AUTO or 4WD HI positions at a given road speed. Take care not to overspeed the engine and do not exceed 25 mph (40 km/h). Proper operation of 4 wheel drive vehicles depends on tires of equal size, type and circumference on each wheel. Any difference in tire size can cause damage to the transfer case. Because 4 wheel drive provides improved traction, there is a tendency to exceed safe turning and stopping speeds. Do not go faster than road conditions permit. WARNING! Always engage the parking brake when powering down the vehicle if the Service 4WD light is illuminated. Not engaging the parking brake may allow the vehicle to roll which may cause personal injury. NOTE: Do not attempt to make a shift while only the front or rear wheels are spinning. This could cause damage to driveline components.