This mightn’t be too hard to figure out as the GU Patrol used a purely mechanical engagement system for the transfer case and four-wheel-drive system. Unlike newer designs with rotary knobs and electronic control, there’s really not to much to go wrong with the Patrol’s setup assuming it’s a selector problem. Make sure the selector rods are all connected properly and that they’re not binding or loose under the car.

However, if the lever is engaging and the front drive-shaft is not turning the front wheels, then you may have a hub problem. Free-wheeling hubs are great for saving fuel, but when they go wrong, it can often mean the drive doesn’t reach the front wheels. At that point, you have a bigger job on your hands. The same symptoms could also be a result of a broken front differential which is not sending the drive out to the front wheels. Finally, the transfer-case itself may be at fault. If it’s not sending the drive forward, there’s no way the vehicle will achieve four-wheel-drive.

Also, to maximise your chances of engaging four-wheel-drive, make sure the vehicle is stationary at the time and the transmission is in neutral. In fact, this is essential for moving between two and four-wheel-drive in many types of off-roader.

While the ZD30 engine should have been a major step forward in terms of technology with common-rail technology and double overhead camshafts, in reality, the engine was not one of Nissan’s finest moments. Bottom end failures were not uncommon with cracked pistons necessitating full rebuilds.

Several causes have been suggested including poor fuel-air ratio management and boost spikes form the turbocharger putting sudden, huge loads on the engine’s internals. Either way, though, the engine is far from remembered fondly.

CarsGuide has looked at this engine in depth, and even published a guide to the Nissan Patrol ZD30 engine.

If your can manually force the shift then there’s probably nothing wrong with the actual gearbox and its mechanicals. Instead, the problem is likely to be an electronic one, perhaps with the speed sensor that tells the computer the car’s road speed and tailors the gearshifts to reflect that. Don’t forget, however, that gearboxes like the Nissan’s with many gears, often won’t select higher gears at low speeds. So if the car refuses to select sixth or seventh gear at urban speeds, that’s possibly just the calibration Nissan has fitted to it.

If this is an actual problem (and not just a characteristic) this is a very new vehicle and would be covered for this sort of problem by the factory warranty.