Audi S6 Diesel: Preheater Fault Symptoms Exposed

As someone with moderate DIY repair experience, I dealt with a very similar issue on my 2018 Audi A6 diesel. The symptoms you describe match exactly what I encountered with the ignition system, particularly the engine preheat indicators. In my case, the heating module was malfunctioning due to a damaged cable connection. The workshop diagnosed it using their diagnostic tool and found that the connection between the control unit and the heating element had deteriorated. The repair involved replacing the faulty wiring and checking the entire preheating system for additional issues. The total repair cost was 95 Euro, which covered both diagnostics and the repair of the defective part in the car electronics. The fix was relatively straightforward once properly diagnosed, and the smoke issues disappeared completely after repair. For a more accurate assessment of your situation, could you provide: Current mileage, When did these symptoms first appear, Any recent repairs or maintenance, Engine temperature when these issues occur, How long does the preheating lamp stay illuminated This information would help determine if your issue is identical to what I experienced or if there might be other factors at play.

Thanks for the input. I had my last service at 120000 KM. The symptoms started appearing around 500 KM ago. The vehicle heater warning lights come on regardless of engine temperature, even after the engine is fully warmed up. No recent maintenance beyond the scheduled service. After reading about similar cases in the forums, I checked the preheating unit connections but they appear intact. The control unit diagnostic codes point to an electrical issue, but I want to be certain before replacing parts. The smoke during acceleration has gotten worse over the past week, making me think the engine preheat system might be failing progressively. Has anyone tried cleaning the connections before going for a full replacement of the control unit?

Since my earlier experience with the heating module issue on my A6, I learned a bit more about the engine preheat system. The worsening smoke you mention is very typical of a failing preheating unit, and its quite different from my initial wiring problem. Based on the diagnostic codes and progressive deterioration you describe, this sounds more like a failing control unit rather than just connection issues. In these cases, cleaning connections rarely solves the underlying problem when the preheating lamp stays continuously illuminated. After my first repair, I actually encountered a similar situation at around 130000 KM where the entire preheating control unit needed replacement. The symptoms matched yours exactly, constant warning lights and increasing smoke during acceleration. The ignition system was struggling to properly manage the engine preheat cycle. A defective part in the control unit itself was the culprit, not the wiring. The repair cost was higher at around 450 Euro, but it completely resolved both the smoke and warning light issues. If your diagnostic codes are pointing to an electrical fault in the control unit, I would recommend going straight for the replacement rather than attempting temporary fixes. Would strongly suggest having the complete preheating unit inspected at a workshop, as partial repairs often end up being more costly in the long run with these particular systems.

Thanks for all the detailed feedback everyone. Given the similarities to other cases and the progressive nature of the symptoms, I think Im convinced its the preheating unit itself thats failing. The car electronics are showing clear signs of an electrical fault in the control unit, and the constant warning lights match what others experienced. My vehicle heater symptoms seem more severe than just connection issues, especially with the smoke getting worse during acceleration. Will book it in for a proper diagnosis and likely replacement of the complete preheating unit rather than waste time with temporary fixes. The ignition system problems others described match my situation too closely to ignore. Really helpful to hear about the actual repair costs and experiences. Better to fix it properly now before the cold season starts and the engine preheat system becomes even more critical. Will update the forum once I get it sorted in case others run into similar preheating control unit failures.