A technician is performing a pre-purchase inspection on a four-wheel-drive (4WD) vehicle. They select '4HI' (four-wheel drive high range) on the transfer case selector. Which of the following statements BEST describes the typical operation of a part-time 4WD system in this mode?
- APower is sent only to the rear wheels, with the front wheels engaged only when slippage is detected.
- BPower is continuously sent to all four wheels, with a center differential allowing speed differences.
- CPower is split evenly (or near evenly) between the front and rear axles, and the center differential is locked.
- DPower is sent only to the front wheels, and the rear wheels are engaged for additional traction.
Show answer & explanationAnswer & explanation
Correct answer: C. Power is split evenly (or near evenly) between the front and rear axles, and the center differential is locked.
In a part-time 4WD system, selecting 4HI typically engages both front and rear drive axles, providing a fixed, direct connection between them. This means power is split between front and rear, and the center differential (if present, often locked in this mode or absent) does not allow for speed differences between the axles. This mode is intended for loose surfaces where tire slippage can occur.
Why the other options are wrong
- A. This describes a 'demand' or 'on-demand' AWD system, not part-time 4WD 4HI.
- B. This describes a full-time 4WD or AWD system with a center differential, not part-time 4WD 4HI where the center is typically locked.
- D. This describes a FWD vehicle with an 'on-demand' rear axle, not a traditional part-time 4WD.
Part-time 4WD (4HI)
Part-time 4WD in 4HI mode provides a direct, fixed power split to both front and rear axles, typically locking the center differential (if present). It is designed for off-road or slippery conditions where wheel slip can relieve driveline binding.
- Engages both front and rear drive axles.
- Center differential is typically locked or absent.
- Not for use on dry, paved surfaces due to driveline binding.
- Provides maximum traction in low-traction environments.
Memory trick: Part-time 4HI, both axles tied, for slippery rides.