Running on after the ignition is switched off is more of a problem in petrol engines than diesels. But you haven’t told me which engine your Triton has, so maybe it’s the 2.4-litre petrol we’re dealing with here. If so, you may find that the running-on is being caused by poorly timed ignition which could suggest a problem with the physical bits that make up the ignition system, or even a problem with the computer that controls it all. Worn or leaking fuel injectors could also cause this problem.

If your engine is the turbo-diesel, then another potential cause of running on is a worn or stretched timing chain (the petrol engine uses a toothed timing belt which shouldn’t stretch) that has allowed the camshaft to get slightly out of phase with the crankshaft. In both these cases, the fault could easily be enough to trigger the check-engine light and keep it on to alert you to the problem. Have the vehicle scanned to see if there’s an ignition fault or what’s called a camshaft deviation, indicating a worn timing chain.

You don’t tell us why your ute needs a new head at just 134,000 km, so it’s hard to comment. If nothing untoward has happened to cause the problem, like overheating, then you could try and convince Mitsubishi to cover the cost of repairs, but unless you have a full history that clearly points to a manufacturing fault I think you would struggle to justify a claim.

If the suction control valve is worn or there is contamination present the fuel pressure will be affected and so will the drivability as a consequence. The car will sometimes go into limp home mode when this happens. It is a relatively common complaint on common-rail diesels, and the only thing to do is to replace the valve.