Audi S4 Power Loss Linked to Faulty Crank Sensor

Having some experience working on Audis, I faced nearly identical symptoms with my 2014 S5 last summer. The engine light came on and the car felt like it was running on half its cylinders. The crank sensor failure caused inconsistent readings, making the ECU unable to properly time fuel injection and spark. My initial thought was timing chain, but diagnostic tests confirmed it was the crankshaft position sensor throwing incorrect reference values. The repair involved: Full diagnostic scan, Replacing the crank sensor, Clearing fault codes, Test drive to confirm proper operation Total cost was 340 Euro including parts and labor. After replacement, power returned to normal and fuel consumption improved significantly. Can you share a bit more about your S4: Current mileage, Any recent maintenance or repairs, When symptoms first appeared, Any unusual noises before power loss, Whether symptoms are constant or intermittent This information would help determine if your issue matches what I experienced or if there might be additional factors to consider. The cam sensor and other timing components should also be checked as they can show similar symptoms.

Thanks for the detailed reply. My S4 has 109837 KM on the clock, and symptoms started about 2 weeks ago after my last routine service. The power loss seems consistent throughout, no unusual noises noticed. The timing between the crankshaft and camshaft seems off based on the scan data, suggesting either a sensor issue or possibly timing chain concerns. Good to hear your fix was straightforward, hoping mine turns out similar with just a sensor replacement rather than major timing work.

The symptoms you describe occurring right after service definitely mirror my experience. When my S5 showed similar issues, I first suspected a timing chain problem, but the reference value discrepancy between crankshaft and camshaft turned out to be purely sensor-related. The fact that your symptoms started after routine service raises an interesting point. Sometimes, cleaning procedures during service can affect sensor connections or wiring. The timing chain on these engines is generally robust at your mileage, so a crank sensor issue is more likely. My repair started with intermittent problems that became constant, just like yours. The consistent power loss you mention matches the pattern of a failing crank sensor rather than timing chain wear. In my case, the engine synchronization returned to normal immediately after sensor replacement. Quick diagnostic tip: if your scan shows fluctuating reference values while the engine is at steady RPM, its almost certainly a sensor problem. This was the key indicator that helped identify my issue before any parts were replaced. Considering the parallels between our cases and the timing of your symptoms, I strongly suspect youll be looking at a similar repair cost and solution as my 340 Euro sensor replacement.

Thanks for all the specific info. Given the similarities with your case, I feel more confident its likely sensor-related rather than a major timing chain issue. The identical power loss symptoms and timing data discrepancies point toward a straightforward fix. The part about cleaning procedures potentially affecting sensors during service makes a lot of sense, since my issues started right after. Before spending money on major repairs, Ill have them focus first on checking both the crank and cam sensors thoroughly. Really appreciate the tip about watching for fluctuating reference values during engine synchronization checks. Ill ask my mechanic to specifically monitor this during diagnosis. Hoping the fix ends up being as simple and affordable as your 340 Euro sensor replacement. Will update once I get it sorted to help others who might face similar issues.