S6 Diesel Glow Plug Issues: Warning Signs & Fixes

I encountered a similar glow plug issue with my 2021 Audi A6 diesel. Having some experience with diesel engine repairs, I can relate to your cold start problems. My diesel car showed comparable symptoms, persistent glow plug light and rough engine performance during cold starts. The engine misfire was particularly noticeable in the morning. After the engine light came on, I took it to a workshop where they diagnosed a faulty glow plug in cylinder 2. The repair involved: Complete diagnostic scan, Removal and testing of all glow plugs, Replacement of the defective glow plug, System reset and cold start verification Total cost was 440 Euro including parts and labor. The fix resolved both the cold start issues and the rough running. The engine now starts smoothly even in cold conditions. To provide more specific advice for your case, could you share: Current mileage, Whether you notice any specific cylinder misfiring, If you have access to the exact error codes, When the symptoms first appeared, Any recent maintenance history These details would help determine if your issue matches what I experienced with my vehicle.

Last service was done at 142712 KM, and I finally got the error codes from the diagnostic scan. The check engine light shows P0671 and P0685. The rough idle seems to be getting worse, particularly in cylinder 3. The diesel engine shakes noticeably during the first 2-3 minutes after cold starts. My fuel efficiency has also dropped by about 15% since these issues began. Interesting that your repair costs were around 440 Euro. Did this include the control module check? The workshop is suggesting I might need the entire glow plug control unit replaced, not just the individual plugs.

Based on those error codes and symptoms, your situation seems more complex than what I initially faced with my Audi. While my repair only needed a single glow plug replacement, your P0685 code points to a potential control module issue, which explains the higher repair estimate. The declining fuel efficiency and rough idle during cold starts definitely match the pattern of glow plug system problems in these diesel engines. The shaking in cylinder 3 suggests the issue might be more widespread than my case. My 440 Euro repair did not include control module testing, it was strictly for diagnostic work and replacing the faulty glow plug. When the control unit itself needs replacement, costs typically run much higher. The complete glow plug control module replacement on my previous A6 diesel ended up costing 890 Euro. Looking at your symptoms: Constant preheating light, Multiple error codes, Rough idle specifically in cylinder 3, Decreased fuel efficiency, Progressive worsening of cold start issues I would agree with your workshop about checking the control unit. These symptoms suggest a systemic issue rather than just a single faulty glow plug like in my case.

Thanks for the detailed information about your experience. After hearing about your repair costs and control module situation, I think I should prepare for a more extensive repair than initially hoped. The check engine codes and symptoms you described match my situation perfectly, especially the rough idle and fuel efficiency drop. Since my engine combustion issues are getting worse and the diagnostic points to both glow plug and control module problems, I will go ahead with the full system check the workshop suggested. I will request they perform a complete diagnostic of the control unit first, before replacing any parts. Given the persistent preheating light and the error codes, this seems like the most logical approach. My main concern is getting the cold start system working properly again before winter, even if it means paying more than the 440 Euro you mentioned for the simpler repair. Will update once I get the full diagnosis and know whether I need just the glow plugs replaced or the entire control module.