Audi S4 Diesel: Glow Plug Control Issues & Smoke Alert

I had a very similar issue with my 2019 Audi A4 diesel engine. As someone with some hands-on experience working on diesel engines, I recognized these symptoms immediately. The continuous preheating lamp and engine misfire symptoms matched my case exactly. After running a diagnostic test, my mechanic found that the cable connections to the glow plug system were damaged, causing intermittent contact issues. The smoke during acceleration was a clear indicator of incomplete combustion due to the glow plug system not functioning properly. The repair involved replacing the damaged wiring and checking all glow plug connections. Total cost was 95 Euro for parts and labor, which seems reasonable for this type of repair. Before suggesting more specific solutions, could you provide: Current mileage on your S4, Whether the check engine light came on gradually or suddenly, Any unusual sounds during cold starts, History of previous glow plug system repairs These details would help confirm if your issue matches what I experienced with my A4. Proper car maintenance of the glow plug system is crucial for diesel engine performance, especially during cold weather operation.

Last service completed at 163978KM. The check engine light appeared suddenly two days ago, unlike in your case. After running a second diagnostic test yesterday, it showed error code P0670 which points to the glow control unit. My vehicle stalling during cold starts has become more frequent, occurring 4-5 times this week alone. The diesel engine makes a distinct rattling noise for about 10 seconds during cold starts, then settles. No previous repairs on the glow plug system since purchasing the vehicle. Based on the symptoms you described, it seems our issues are similar, though mine might be more severe given the consistent vehicle stalling. Was your smoke also greyish white during acceleration? Mine seems to worsen particularly after the engine has been running for about 15 minutes.

Thanks for those additional details. Your symptoms definitely sound more severe than what I experienced with my A4. The error code P0670 combined with the vehicle stalling and distinct rattling noise strongly suggests a failing heating element in the glow control unit, rather than just the wiring issues I had. The greyish white smoke after 15 minutes of running is particularly telling. In my case, the smoke was lighter and mainly visible only during initial acceleration. The persistent smoke in your case, combined with the engine misfire symptoms and frequent vehicle stalling, indicates the glow plugs arent reaching proper operating temperature. My repair was relatively simple at 95 Euro, but given your symptoms point to a faulty control unit rather than just wiring, you might be looking at around 350 Euro for parts and labor. The good news is that replacing the glow control unit typically resolves all these symptoms simultaneously, the smoke, cold start issues, and the warning lights. Would recommend getting this addressed soon, as continued vehicle stalling could lead to additional engine damage. Have you noticed any changes in fuel consumption since these symptoms started?

Thank you for sharing those details about your repair costs. Interesting to hear your case was primarily wiring-related, as my symptoms do seem more aligned with a complete glow control unit failure. The fuel consumption has actually increased by about 15% since these issues started. Considering the vehicle stalling frequency is increasing and the heating element is clearly malfunctioning based on the error code, I will proceed with the control unit replacement. The 350 Euro estimate seems reasonable given the scope of work needed. The diesel engine symptoms match the diagnosis, and waiting longer could indeed lead to more expensive repairs. Will schedule the repair this week to address the cold start problems and prevent any potential cascade of issues. The consistent engine misfire during startup and that rattling noise definitely have me concerned about potential long-term damage if left unaddressed.