2023 Isuzu NPS Pricing and Specs

The first question to ask is have you changed the way you drive the vehicle. Driving style has a huge bearing on fuel economy, and if you’ve started to drive the vehicle harder or even on roads that are more winding and hilly than before, a jump in fuel consumption is common. On that level, is it just you driving the vehicle or is somebody else using it lately who might have a heavier foot than you?

Have you added a roof rack or more weight in the form of a winch. Even a new set of more aggressive or larger diameter tyres can do terrible things to fuel economy. But if the answer to all that is no, then you need to have the car scanned to see if any fault codes are thrown up by the computer. And when was the engine last tuned? Is the air cleaner free of dust and are the fuel injectors working as efficiently as they should be?

This sounds like a rear differential problem. The differential is designed to allow the inside and outside wheel of that axle to rotate at different speeds (which they need to do as the inside wheel describes a smaller arc than the outside wheel in a corner). If something goes wrong inside the differential, that function can be lost and the wheels try to turn at the same speed in corners. When that happens, the rear end will skip and jump about as the two rear wheels effectively fight each other.

Limited-slip differentials (LSD) often have this problem when the clutches that control the amount of lock-up in the differential fail or become worn. At that point, similar jumping and clunking noises can be felt and heard. In some cases, a limited-slip differential can be restored to health with a change of fluid and perhaps an additive, but in other cases, the unit must be rebuilt.

The rear differential in your D-Max should be the limited-slip type, but around this time, Isuzu made the LSD an option, so it would be worth checking. If it’s an LSD, a fluid change would be the first step towards sorting this problem.

The first thing to check is the fluid level in the transmission. Consult the owner’s manual for the correct method of doing this (sometimes the engine needs to be running and the transmission at operating temperature, in other vehicles everything needs to be cold, so this is important).

Low transmission fluid can cause all sorts of problems with gear selection, flaring between gears and actually making the vehicle drive, so that’s why this is the first step. If the level (and the condition) of the fluid is fine, then you need to start looking deeper, and a transmissions specialist is probably your best bet there.

The transmission is a sealed system, so any drop in the fluid level suggests a leak somewhere that needs to be fixed or the problem will return.

Beyond that, running a transmission that isn’t behaving properly can cause damage to the unit itself, so continuing to drive the vehicle in this state is not a good idea.