Audi S4 Diesel Glow Plug System Failure Warning Signs

Had the exact same symptoms on my 2016 Audi A4 3.0 TDI. The control unit for the vehicle heater was sending incorrect signals due to damaged wiring connections. After thorough diagnostics, the issue was traced to corroded plug connections between the heating module and the main control unit. The repair involved: Complete inspection of the preheater system, Replacement of damaged wiring harness, Installation of new plug connectors, Reprogramming of the heating control unit The constant preheating lamp and performance issues are serious warning signs that should not be ignored. Continuing to drive with these symptoms can lead to increased fuel consumption and potential engine damage. The smoke during acceleration typically indicates the car electronics are not properly controlling the fuel mixture due to faulty signals from the heating system. Getting this fixed promptly is crucial for preventing more extensive engine problems. For reference, my repair required the vehicle to be at the shop for 2 full days, as accessing the components behind the engine required significant disassembly. This is not a quick fix, but addressing it early prevents more costly repairs later.

Thanks for sharing your experience with the preheating unit issues. Your repair process sounds exactly like what my mechanic suggested might be wrong with my S4. Good to hear it was fixable. Can you remember roughly how much the total repair cost? Also wondering if youve had any similar issues pop up since the fix? My ignition system has been acting up lately too, so trying to determine if these problems might be connected.

Great news, since my last post about the preheating control unit problems, the repair has been completely successful. The mechanic fixed the defective cable connections to the preheating unit, which only cost 95 Euro. Much cheaper than I expected, since it was just the connector that needed attention rather than replacing the entire heating module. The car preheater system has worked flawlessly since the repair. No warning lights, no smoke issues, and the engine preheat cycle runs normally now. Regarding your question about ignition problems, in my case, they were definitely connected. Once the preheating unit was properly fixed, all starting issues disappeared completely. It sounds like your symptoms match what I experienced exactly. A faulty connection in the preheating system can definitely cause those ignition issues youre describing. The defective part in your case might also just need a connection repair rather than full replacement, which could save you significant money.

Thanks everyone for the helpful replies. I finally took my S4 to a different mechanic last week and got everything sorted out. The electrical fault turned out to be exactly what was described, damaged wiring to the preheater control unit. The repair took about a day and a half. They replaced the wiring harness and a few connectors, then did a full system reset. Total cost came to 180 Euro for parts and labor, which was much better than I feared. No more smoke, warning lights are gone, and the car starts perfectly even in cold weather. Really glad I asked here first, helped me understand the problem better before going to the shop. The mechanic confirmed the ignition system issues were definitely connected to the faulty preheater unit. Everything is running smoothly now.