unlocked and allows for a variable front:rear torque split that ranges from 0:100 to 100:0, or anywhere in-between. Up to 100 percent of torque can be sent to the front wheels, via "torque biasing" for temporary front-wheel drive, in extreme situations where the rear drive axle loses complete traction. High range gearing is used. For use in all-weather on road (dry, wet or slippery pavement) conditions or light off-road conditions. |- ! Four High (4H) | All-wheel drive(locked) | The intelligent locking center multi-disc differential is locked providing a permanently locked 50:50 torque split. The front and rear drive shafts are mechanically locked together forcing them to turn together with absolute zero rotational speed difference. High range gearing is used. Not for use on pavement, only for off-road conditions. If Four High mode is used on pavement, torque windup and drivetrain binding can occur resulting in catastrophic driveline failure. |- ! Four Low (4L) | All-wheel drive(locked) | Similar to Four High mode in operation, the permanently locked 50:50 torque split is maintained; however, low range off-road reduction gearing is engaged. A default off-road program is automatically selected and remaps (reprograms) the electronic throttle control, traction control system (engine control), and turns off AdvanceTracs electronic stability control and roll stability control safety systems for off-road use. The four-wheel electronic traction control system (brake differential locking control) remains active and continues to function as normal. Not for use on pavement, only for off-road conditions. If Four Low mode is used on pavement, torque windup and drivetrain binding can occur resulting in catastrophic driveline failure. |} 4WD Expeditions come with standard dual front frame-mounted closed-loop recovery hooks and available off-road underbody protection. Steel plates are placed over vital areas with a composite shield for the fuel tank. Expedition 4x4s are tested alongside the F-150 and Super Duty trucks at Ford's California and Arizona proving grounds. Expedition is put through the same durability tests and evaluations to meet the same durability standards as its pickup truck brethren. Traction control Rear-wheel drive or all-wheel drive have conventional open-type differentials with a choice of axle ratios. Traction control systems, both mechanical and electronic, are optional.Mechanical traction control (1997–2006) Both first and second generation Ford Expeditions (UN93 and U222) had an optional Traction-Lok rear limited-slip differential (LSD). The clutch packs inside the LSD tend to be weak, will wear over time, gradually losing their ability to