Audi S6 Diesel Glow Plug Issues Causing Rough Running

I had a very similar issue with my 2017 Audi A6 diesel engine. As someone with moderate experience in car maintenance, these symptoms immediately pointed to electrical issues in the glow plug system. The engine misfire and rough running were particularly concerning. After some basic troubleshooting, I took it to a workshop where they diagnosed a faulty cable connection to the glow plug control unit. The repair involved replacing damaged wiring and securing proper connections, which resolved both the continuous preheating lamp and engine performance issues. The total repair cost was 95 Euro. Before committing to repairs, make sure to: 1. Check for error codes using an OBD scanner 2. Inspect visible wiring around the glow plugs for obvious damage 3. Monitor if vehicle stalling occurs when the engine is warm To provide more specific guidance, could you share: Current mileage on your S6, Whether these symptoms occur only during cold starts or all the time, If any recent maintenance was performed on the glow plug system, The outside temperature when these issues typically occur This information would help determine if your case matches what I experienced with my A6.

Thanks for your reply. My vehicle has 85739 KM and had its last service 3 months ago. The symptoms mainly occur during cold start conditions, especially when temperatures drop below 10C. The heating element issues seem most pronounced in the morning. The engine light came on just recently, about a week after I first noticed the continuous preheating lamp. After reading about your experience, I checked the wiring connections as suggested but found no visible damage. I will get an OBD scan done this week to identify specific error codes. The engine misfire is definitely more noticeable during initial startup compared to when the engine is warm. I am planning to have it checked at a workshop soon, as the car maintenance schedule suggests glow plug inspection at 90000 KM. Would it make sense to do this service earlier given these symptoms?

Thanks for the additional details about your S6. Based on your description, especially the timing of symptoms with cold starts and the recent appearance of the engine light, this does sound quite similar to what I dealt with on my A6. The fact that the issues are more pronounced below 10C strongly suggests a glow plug system problem rather than just a wiring issue like I had. Since your vehicle is approaching the 90000 KM service interval for glow plug inspection, I would absolutely recommend getting this done now rather than waiting. In my subsequent research after my repair, I learned that these heating element failures often cascade, when one starts to fail, others typically follow. A proper diagnostic test can identify which glow plugs are underperforming. In my case, I wish I had done this earlier, as vehicle stalling became more frequent before I addressed the issue. Regarding the three-month-old service, did they perform any work near the glow plug system? Sometimes disturbing these connections during other maintenance can trigger similar symptoms. I would suggest getting both the OBD scan and glow plug inspection done together. The total cost should be reasonable compared to risking further damage from continued cold starts with a compromised system.

Thanks for sharing that detailed information about your A6 repair experience. Given that my symptoms occur mainly during cold start conditions and worsen below 10C, I agree it makes sense to address this sooner rather than later. I checked my service records and no work was done on or near the glow plug system during the maintenance 3 months ago. Since my diesel engine is showing these clear preheating issues and I am approaching the 90000 KM service mark, I will schedule both the diagnostic test and glow plug inspection this week. The continuous preheating lamp combined with rough running during cold starts definitely seems to point toward the heating element system rather than just wiring. I appreciate your insight about how these failures can cascade, that helps explain why the symptoms have gotten progressively worse. I have already scheduled an OBD scan for tomorrow and will get the full glow plug inspection done right after. Better to address this proactively rather than risk additional engine damage from continued cold starts with potentially failing glow plugs. Will update once I have the diagnostic results and know exactly what needs replacing.