SQ7 VANOS Solenoid Fault Spikes Fuel Consumption

Had this exact issue on my S5 (2018) last winter. The symptoms match what you describe, increased fuel consumption and check engine light coming on repeatedly. After diagnostic tests, it turned out to be a VANOS failure caused by a defective inlet camshaft solenoid valve. The variable valve timing system malfunction was causing the engine misfire and poor fuel economy. The timing chain showed normal wear, but the solenoid valve had completely failed. This is actually a serious issue that needs immediate attention, as continued driving can lead to further engine damage and even more expensive repairs. When the VANOS system fails, it cant properly adjust valve timing, leading to rough running and decreased performance. The repair involved replacing both the solenoid valve and cleaning the entire VANOS unit to prevent future issues. Would strongly recommend getting this checked by a qualified technician who specializes in these engines. Its not a DIY job due to the complexity of the timing system and the precision required for proper VANOS adjustment.

Thanks for sharing your experience. Your symptoms definitely sound similar to what I went through with my SQ7 last year. The check engine light and fuel consumption issues were really concerning at first. Since you mentioned getting it fixed, did you remember roughly what the final repair cost was? Also curious if you have had any related problems pop up since the VANOS repair was done? Mine has been running fine after the fix but always good to know what to watch out for with these variable timing systems.

Thanks for asking about the follow-up. After getting the VANOS solenoid issue fixed on my S5, everything has been running perfectly for the past months. The repair specifically addressed a faulty inlet VANOS solenoid valve which was causing the low power and variable timing problems. The total cost came to 250 Euro for replacing the defective camshaft solenoid valve. This was actually reasonable considering the complexity of the BMW VANOS system and the precision needed for the repair. Since the fix, fuel consumption has returned to normal and the check engine light hasnt appeared again. The engine response is much smoother now, especially during acceleration. Would definitely recommend getting any VANOS-related issues checked quickly, as catching these problems early typically means a simpler repair job. Have had zero issues with the variable timing system since the repair. Regular oil changes and using the recommended grade seem to help prevent future VANOS failures. Just keep an eye on any unusual engine sounds or performance changes, as these can be early warning signs.

Thanks for the input. I finally got my car checked and fixed last week. The mechanic confirmed it was indeed a VANOS solenoid problem causing the variable timing issues. After running diagnostics, they found significant oil sludge buildup affecting the VANOS system. The total repair came to 280 Euro, which included cleaning out the VANOS unit and replacing the faulty solenoid. They also did a complete oil system flush to prevent future problems. The whole job took about 4 hours. My SQ7 is running much better now, fuel consumption is back to normal and the check engine light has stayed off. The low power issues I was experiencing have completely disappeared. The engine feels much more responsive, especially during acceleration. Really glad I got this sorted quickly before it could cause more extensive damage. Will definitely be more proactive with maintenance going forward to prevent oil sludge from building up again.