The JL4 RPO code denotes a four-wheel drive system for certain General Motors vehicles. This system utilizes an electronically controlled transfer case to send power to the front and rear axles. The JL4 option was first introduced in 1999 on the Chevrolet Silverado and GMC Sierra 1500 models. It has since been made available on a number of other GM vehicles, including SUVs and trucks.
The main advantage of the JL4 system is its improved traction and stability compared to traditional two-wheel drive systems. This makes it ideal for driving in off-road or inclement weather conditions. It also offers a smoother ride than older four-wheel drive systems that used manual locking hubs.
If you're considering a GM vehicle with the JL4 option, be aware that it does come at a premium price. However, many drivers feel that the added safety and peace of mind are well worth the extra cost.