This is a pretty well known problem with the three-litre turbo-diesel that Toyota was fitting to Prados between 2009 and 2014. The problem began when Toyota redesigned the pistons of the engine to help it achieve Euro 4 emissions standards. Earlier versions of the motor that didn’t comply with Euro 4 did not have the same problem.

The piston cracking most commonly occurs once the engine has covered something like 100,000km or 150,000km. It was also most likely to occur in engines that had been modified to produce more turbo-boost or vehicles that had been used for extended periods of towing heavy loads.

Toyota did issue a service bulletin for the problem and began fitting post-2014 engines with different fuel injectors and a revised piston design. Piston failures in these later engines are rarer but still not entirely unknown. Even though a service bulletin was issued, Toyota did not issue a recall for the affected vehicles.

The first thing to check is the level of the transmission fluid. If this is incorrect, it can cause all sorts of drive and shifting problems. Also, how long since this vehicle had its automatic transmission serviced? We tend to forget that these hard working components benefit from a periodic change of filter and fluid and a general check-up to make sure there’s nothing that needs adjusting inside the gearbox.

The reason the transmission begins to feel better after it’s warmed up is possibly to do with the temperature of the fluid and the friction surfaces inside the transmission. When the gearbox and fluid are cold, the fluid is thicker (and harder to pump) and can’t lubricate or operate the transmission as effectively. Even so, the gearbox should not shift harshly even when it’s cold. When it does, it’s trying to tell you something.

Before you buy more parts that may or may not fix the problem, have the vehicle electronically scanned. This is by far the most cost-effective way of finding out what’s wrong and then being able to tackle the actual problem. You could spend weeks and months, not to mention hundreds and thousands of dollars, replacing random parts that have no relationship to what’s causing the engine to refuse to start.

There are literally thousands of reasons for the symptoms you’ve noted, so try to finding the root cause before committing to more replacement bits and pieces.