Vauxhall Vectra Crankshaft Sensor Issue

A 'crankshaft to camshaft reference value' error could indeed point towards the crankshaft sensor. However, have you considered a timing chain issue? Though the crankshaft sensor failing seems more likely, it would be prudent to rule out timing chain wear, especially given the mileage. Is the engine making any unusual noises?

I haven't noticed any unusual noises that might suggest a timing chain problem. However, I will try to ascertain for sure. Is there a reliable way to assess the timing chain without dismantling the engine and having a look at it? Is a misfire possible in that setting?

Without physically inspecting the timing chain, a precise diagnostic may prove difficult. Misfires are definitely possible with timing issues, and could present as the symptoms you're experiencing, or not, depending on severity. Given the reference value error code, and if noise is not present, the crankshaft sensor appears as the culprit. I suggest confirming with a qualified mechanic before purchasing parts.

Following your advice I went to a workshop. It was indeed the crankshaft sensor, and after replacement, the problem is gone. The total repair cost was 340€.