Audi A4 Diesel: Glowplug Issues Cause Engine Trouble

I dealt with a very similar problem on my 2020 Audi A6 diesel last winter. Have moderate experience with diesel engine maintenance, though I always rely on professional diagnosis for electrical issues. The symptoms matched exactly what you describe, constant preheating lamp, check engine light, and smoke under acceleration. The diagnostic test pointed to issues with the glow plug system. Turned out the cable connection to the glow plug control unit was damaged, causing inconsistent heating element function and engine misfire issues. Had it fixed at a workshop, total cost was 95 Euro for diagnosing and repairing the faulty connection. The repair prevented potential damage to the glow plugs themselves, which would have been much more expensive to replace. Would strongly advise against driving the vehicle until repaired, as continued operation with faulty glow plug operation can cause carbon buildup and affect engine performance. To provide more specific guidance, could you share: Current mileage on your A4, When was the last glow plug system maintenance, Are you noticing any hard starting, especially in cold weather, Have you scanned for specific error codes

Last service done at 44000 KM, currently at 45592 KM. The glow plug issue turned out to be a wiring problem in my case. The cold start became increasingly difficult before vehicle stalling started occurring. After proper diagnosis, technicians found moisture had corroded the heating element connections, causing the system to malfunction. After fixing the wiring harness and cleaning the connectors, the diesel engine runs perfectly again. Total repair cost was 180 Euro including diagnostic work. Going to have the glow plugs inspected during next scheduled maintenance as preventive measure. Got it fixed quickly to avoid any potential long-term damage to the injection system. If you notice similar symptoms, especially during cold starts, best to address it immediately.

Thanks for the follow-up on your A4 glow plug repair. My A6 also had similar cold start issues before the problems became more obvious. The corroded connections you mentioned are a common failure point in the glow plug system. The cost seems reasonable for the work done. Had my A6 in for routine car maintenance last month and had them check the entire glow plug system again. The control unit and heating element connections are still working perfectly after the initial repair. A proper diagnostic test is crucial for these issues since vehicle stalling and smoke can have multiple causes. Getting the wiring fixed early likely prevented damage to the glow plugs and injection system. Good call on scheduling a preventive check during your next service. From experience, its worth having the complete system inspected annually, especially the wiring harness and control unit connections, to catch any potential issues before they cause starting problems. Let us know how the car performs over the next few months. These repairs usually provide a lasting fix when done properly.

Since I was the one who asked the initial question, I will provide an update on my A4's performance after the repair: The glow plug system has worked flawlessly since fixing the wiring issue. No more engine misfire problems or difficult cold starts even during colder mornings. The control unit readings are now normal, and the smoke during acceleration has completely disappeared. The car maintenance technician showed me the corroded wiring harness they replaced. The moisture damage was quite extensive, which explains the erratic behavior of the heating elements. Good thing I had it checked promptly instead of continuing to drive with the warning lights on. For anyone experiencing similar symptoms, constant preheating lamp, engine warning light, and smoke, have your glow plug system checked immediately. The 180 Euro repair cost was definitely worth preventing more serious engine problems. My next service is scheduled in 4000 KM, where they will perform a complete inspection of the entire system as preventive maintenance. A proper diagnostic test helped identify the exact issue quickly. These electrical problems can be tricky to diagnose without the right equipment, so professional inspection is essential when dealing with glow plug system faults.