Plenty of owners of this make and model have experienced similar frustrations with the rotary dial not selecting two- and four-wheel-drive promptly and accurately. It’s possibly down to a switch (the rotary dial itself) that has developed wear or play in its mechanism and simply isn’t as accurate as it once was. But it’s also worth checking the electronics that control the shift function, as a glitch might have the system trying to select something other than what’s showing on the dial.

This is a classic case of electronics taking over a mechanical function (early 4WDs had a simple, mechanical lever to switch between two and four-wheel-drive) and not being as good at it. This function, when you think about it, is an incredibly important one for this type of vehicle and might mean the difference between getting out of a bog-hole and not. Many owners would welcome the return of the purely mechanical lever, but that’s not the direction car design is travelling.

It’s quite common for an oil pressure sensor to develop a fault where it sends the incorrect information to the car’s computer which then lights up the low oil pressure warning. But since you’ve already replaced this sensor, maybe that’s not the case here.

The big clue is that fresh oil and filters improved things a little, which makes me think it’s a genuine oil pressure problem. I also reckon you might be bang on the target by suggesting that it’s an oil pick-up problem. The oil pick-up lives in the sump of these engines and if the pick up inlet is blocked or partially blocked by sludge from the engine, it can fail to suck up enough oil to maintain the correct oil pressure. The higher the revs, the bigger the pressure shortfall. Failing that, sludge can block the various oilways around the engine that allow the oil to get to where it needs to be. Either way, you wind up with insufficient oil pressure and flow and risk destroying the engine.

I wouldn’t have thought 136,000km on an engine would have it showing signs of oil sludging, but that’s based on proper maintenance (not to mention that even modern diesels are filthy things inside). Have you owned the vehicle from new? Has it always been serviced correctly and promptly? If it’s been neglected (even one skipped oil change) it can develop the deadly sludge and it can be all downhill from there.

Possibly the best course of action would be to remove the sump and check the oil pick-up strainer for signs of gunk and build up. If that’s okay, then two or three quick oil changes (say, every 1000km) with an engine oil designed for trucks (which has lots of detergent as an additive) might clean things up internally enough to keep the oil pressure light at bay.

The other thing to try would be a new oil pump. Like any engine component, these can wear out over time and kilometres but, again, I wouldn’t expect to see significant wear on one that’s just 136,000km old. Other causes to consider would be excessive bearing clearance in the engine (due to wear or damage). In that case, a tear down and rebuild is the best option, because worn engine parts don’t repair themselves.

Commercial vehicles like the Colorado can often lead a much harder life than passenger vehicles. And that means some areas can wear faster, differential bearings being just one of them. A Colorado that has been used to carry heavy loads or tow heavy trailers could easily be showing wear in the differential at this point.

The other thing that destroys differentials is driving the vehicle through water crossings. As an off-road capable vehicle, this is pretty likely in a Colorado., What happens is that water can enter the differential housing through the breather tube and contaminate the diff’s oil. At which point, wear is accelerated as the differential gears and bearings are no longer receiving the lubrication they need. Floodwater is particularly bad for diffs as it also contains lots of tiny grit particles which act as grinding paste inside the differential.