C4 Diesel Rail Pressure Sensor Fault

That does sound like a faulty rail pressure sensor. Before you go replacing it, have you checked the wiring and connections to the sensor itself? Sometimes a loose or corroded connector can cause intermittent signal issues. Also, what specific code are you getting? Knowing the exact code can help narrow down the possibilities. What happens when you try to rev the engine, any smoke?

Good shout on the wiring, I'll give that a look-see tomorrow in the daylight. The OBD reader just gave a generic 'Rail Pressure Sensor Signal Faulty' message, didn't have a specific code number unfortunately. As for revving, it's hesitant and struggles to get up to speed. It puffs out black smoke when I put my foot down when accelerating. Does that help?

Okay, the black smoke indicates incomplete combustion, which could definitely be linked to incorrect fuel pressure readings from a faulty sensor. Given the stalling, reduced power, and black smoke, combined with the sensor code, it's highly likely the sensor itself is failing. While you could try cleaning the sensor (unlikely to fix it permanently), I'd recommend getting it properly diagnosed at a workshop, especially with the diesel engine. They can confirm the sensor is the issue and check the rest of the fuel injection system. It might save you money in the long run.

Thanks, that's what I was afraid of. I was hoping it was a simple fix, but sounds like it's beyond my limited skills. I'll book it into the workshop. Turns out, the rail pressure sensor was indeed defective. After replacement and diagnosis of the sensor and the wiring, I'm back on the road for 240€. Thanks again!