Peugeot 406 Fuel Consumption CEL

That sounds frustrating! I had similar symptoms on my old Volvo V70 – check engine light and terrible fuel economy. VANOS is BMW's name for their variable valve timing system, but other brands have similar tech, so the principle's the same. In my case, it ended up being a faulty camshaft position sensor. Have you checked those? Also, what codes are you pulling? Could be anything from a timing chain issue to low power to the valves.

Cheers for the quick reply! Good shout on the camshaft sensor, I hadn't considered that specifically. When you say 'codes', what do you mean? And how did you eventually narrow it down on your V70?

By 'codes', I mean the diagnostic trouble codes (DTCs) that the car's computer stores when the check engine light comes on. You need an OBD2 scanner to read them. They'll give you a more specific direction. I'd start there. If it is related to the VANOS system, I'd suggest you take it to the workshop, those variable timing systems can be quite complicated.

Right, gotcha on the codes. Thanks a bunch for pointing me in the right direction! I went to the workshop, plugged it in, and boom – faulty camshaft solenoid valve, just as suspected. New one fitted, power supply checked, and all's good. The bill came to 250€. Runs like a champ again!