SMAX VANOS Solenoid Issue

Sounds familiar. I had a similar issue with my old Vauxhall Insignia, although that was a petrol engine. Check engine light, poor fuel economy, the works. It turned out to be a dodgy camshaft position sensor. Have you had the codes read? That's the first thing I'd do. Could also be oil sludge buildup if the servicing hasn't been spot on.

Cheers for the reply. Yeah, I had the codes read; it's pointing towards the VANOS system specifically, which is why I'm leaning towards the solenoid valve issue. But oil sludge is a good shout, hadn't thought of that. Where exactly was the camshaft position sensor located on your Insignia, and did it throw any other codes besides the generic check engine one?

Okay, VANOS specific codes definitely point to that system, so oil sludge or a faulty solenoid are likely culprits as you suspected. On the Insignia, the sensor was located near the top of the engine, close to the camshaft pulleys, but honestly, the location will be different on your SMAX. Mine also gave a specific camshaft position correlation code alongside the check engine light. If you're getting VANOS specific codes I would take it to a workshop. It cost me 200€ to fix the Vauxhall issue so brace yourself.

Thanks for all the help! It's been sorted now. Turns out it was a faulty camshaft solenoid valve, just like I suspected. Ended up costing me 250€ for the part and labor. Annoying, but at least it's running smoothly again.