Mercedes GLS engine issue VANOS mechanics

I also own a GLS, and I had similar symptoms a while back Check engine light, decreased fuel economy, the works The VANOS system is responsible for variable timing, and when it malfunctions, it throws everything off The inlet camshaft timing is crucial Did the scanner provide any specific error codes A faulty camshaft solenoid valve is a prime suspect, but also look into the wiring harness and connectors leading to the VANOS solenoids A poor connection can mimic a faulty solenoid If you can monitor the VANOS solenoid activation with a scan tool, that's even better Do you have access to one that can do live data

Thanks for the quick reply The error code was PXXXX something related to 'Inlet Camshaft Actuator Control Circuit' I don't have a scan tool that can show live data, unfortunately I only have a basic OBD2 scanner Is there a way to check the wiring harness and connectors without specialized tools I'm willing to get my hands a little dirty before taking it to the shop

That code pretty much confirms the inlet camshaft VANOS issue You can visually inspect the wiring harness for any obvious damage – frayed wires, cracked insulation, corroded connectors Unplug the connector to the solenoid and look for corrosion on the pins Clean them with electrical contact cleaner if you find any However, without live data, it's hard to pinpoint the exact cause Given the symptoms and the error code, it's highly likely the solenoid valve needs replacing You could try swapping the inlet and exhaust camshaft solenoid valves as a diagnostic step if they are the same part number, but I'd advise against it unless you're confident Honestly, at this point, I'd recommend taking it to a reputable shop They can properly diagnose the issue and replace the faulty component The eventual repair cost for me was around 250€

Thanks a lot for the detailed explanation and advice I checked the wiring harness as best as I could, and didn't see anything obvious, so I took it to my local mechanic Turns out it was indeed the inlet camshaft solenoid valve Replaced it, and the check engine light is gone, and the car runs like new Fuel consumption is back to normal as well The final bill was almost exactly the same you predicted I appreciate your help in narrowing down the problem