On this model, the sensor in question is located on the crankcase (not the cylinder head as many are). You’ll find it on the driver’s side of the crankcase, below the intake manifold. Replacing it involves removing the old one by screwing it out, and screwing the new one in. But there’s a bit of a process for this, and if you’re not familiar with this type of job, it’s probably one for the experts.

The sensor is located between cylinders three and four and it’s located pretty close to the manifold. The good news is that you don’t need to remove the manifold to access the sensor; you can get to it by going into the engine bay through the wheel-well.

Don’t forget that you’ll lose some coolant in the process, so that will need to be topped up with the correct type afterwards. Remember, too, that the new sensor won’t work unless you correctly reattach the wiring plug that connects the sensor to the rest of the car. This area can be pretty grimy and muddy in a vehicle like this, so cleaning everything off first is a good idea.

The symptoms here point to a stuck flasher relay. This is the electrical component that not only powers the indicator lights, but makes them flash (and produces the steady clicking sound you hear when the indicators are on). The contacts in these units can become stuck at which point the lights can become stuck on.

Why does it still happen when the ignition is off? Because the flasher relay is powered up even when the ignition is not. That’s so you can have the emergency hazard-warning lights flashing even though the vehicle is locked and the keys in your pocket. A new flasher relay unit should fix it.

This sounds very much like a fuelling problem. Since a diesel engine has no ignition system (beyond its own compression) any fall off in performance can often be traced back to the fuel system.

The best bet is to take the vehicle to a diesel specialist that knows this make and model and will have either seen this exact set of symptoms before or will be able to make a logical diagnosis rather than just changing random parts that may or may not be the cause of the problem. Things that are likely causes, however, are the fuel filtering system, fuel pump and injectors. But don’t rule out something simple like a bad batch of fuel that is playing havoc with the entire system.