Isuzu Problems

Unless the wheel nuts have sheared off or the bearing or axle failed catastrophically, the most usual way for a wheel to fall off a moving car is if the wheel nuts were not torqued properly by who ever removed the wheels most recently. Has the car ever had a new set of tyres? Or was the wheel that jumped ship changed at any stage because the tyre was flat?

Perhaps the best advice is to approach your state motoring club. These clubs often operate a technical inspection service where the cause of faults can be determined and a written report supplied. This is then considered an independent source of evidence and may be helpful if the matter is taken to a dispute hearing.

What you’re experiencing is the transmission calibration that many modern vehicles use to increase fuel economy. By always trying to be in a higher gear, the vehicle will record a better fuel economy number on the official test that compares it with its competitors.

The downside is that the constant upshifting means the vehicle will sometimes find itself in a gear that’s slightly too tall, and that’s when you’ll start to get the symptoms of feeling like the engine is labouring or lugging.

As you’ve noted, when the car shifts down a gear, the sensation goes away. The solution is to manually pull the car back a gear when this happens. If t really bothers you, you could ask Isuzu if there’s a software update that makes the transmission a little less eager to be in top gear.

This is a tricky one because the D-Max’s SVS warning light seems to be a bit of an all-rounder. That is, it indicates a fault, but a non-specific one. Certainly not one that can be read by the majority of aftermarket scanning tools. Logic suggests there’s something within the driveline that is getting too hot for the computer’s liking, a theory backed up by the fact that it only triggers when you’re towing a big load and the car is working its hardest.

The solution seems to be to present the car at an Isuzu dealership as this may be the only workshop that will have the D-Max-specific scanning gear to determine the cause or even narrow it down.

For the record, the SVS stands for Service Vehicle Soon, but I’m afraid even that’s a fairly generic recommendation and doesn’t get you any closer to the cause. That said, when engine oil or transmission fluid gets beyond a certain temperature, the computer will often detect this and call for a change of fluids as a means of driveline protection. This could be what’s happening every time you tow.

The car could be trying to trying to tell you that there’s something wrong with the key. So start with the basics. The most common cause for the key to not operate the ignition and security system (which is why the engine won’t start) is because the key’s battery has gone flat. Change it and see if that works. At the very least, try the second key (that should have come with the car) to see if it will operate things properly.

If not, then you have to start digging deeper, at which point the cause could be a glitch within the car’s body computer which is the brain that controls everything from the power windows to the central locking and immobiliser. If that’s the case, then an auto electrician is probably your best bet, but definitely check the key’s battery first.

A car that’s left to sit for a length of time will often develop a flat battery as things like the clock and security system slowly drain the battery. But this should not happen in just three days.

If there’s absolutely no drain on the battery (as checked by your electrician) then suspicion turns to the battery itself. It may have done this since it was brand-new, but the battery could have a manufacturing flaw or internal damage that means it won’t hold a charge beyond three days. Borrow a different battery and see if the problem goes away.

Not being able to match a vehicle’s official fuel consumption number is not just common, it’s something just about every owner discovers the hard way. That’s because the test that determines the number is a laboratory test, not a real world one. The test figure serves as a comparison between different makes and models, not a realistic expectation of fuel consumption.

However, the additions you’ve made to your car will all increase fuel consumption. A nudge bar and tow bar both add wight and a set of roof bars can easily add a litre of fuel to every 100km travelled thanks to increased aerodynamic drag. Even the GVM upgrade might make a difference, especially if it sits the vehicle up higher, affecting aerodynamics even further. If you’ve also fitted bigger tyres, fuel consumption will rise even more. To be honest, I reckon 10 litres per 100km is about right for this vehicle and matches most other vehicles of this type. Don’t forget, either, that an Isuzu MU-X is a much bigger, heavier vehicle than a Subaru Forester.

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.

It’s difficult to be definitive here without actually driving the vehicle, but there are at least two possible sources for this. The first is the simplest and involves either a wheel and tyre or driveshaft that is out of balance. That should be easy to diagnose and fix.

The second possibility is that the vehicle’s driveline (engine, gearbox and transfer-case) has what’s called a resonant frequency that, when reached at a particular speed range, will result in some weird harmonics and vibrations which is possibly what you’re feeling and hearing. This becomes worse when the torque converter locks up (to save fuel) and there’s no slip in the driveline to absorb these bad vibes. By shifting back to fifth gear, you’re raising the engine revs and moving it out of that harmonic patch.

I’ve heard that Isuzu has been remapping some ECUs (on-board computers) to try to move this harmonic zone into a different (higher) speed range (by manipulating the torque-converter lock-up point) where it won’t be a problem to most owners. The fact is the Isuzu diesel has never been the most refined one out there and some vibrations and harmonics are relatively common, However, they shouldn’t be bad enough to ruin your enjoyment of the car.

In the old days, a different exhaust was often enough to move the harmonics around or get rid of them altogether, but I can understand why that’s not really an option on a brand-new vehicle.