SQ8 Diesel: Glow Plug Warning and Smoke Issues Fixed

I faced similar issues with my 2018 SQ7 diesel about 6 months ago. Having some experience with basic car maintenance, I first attempted standard troubleshooting but quickly realized this needed professional attention. The symptoms were identical, persistent preheating lamp, engine light illuminated, and visible smoke during acceleration. After running a diagnostic test, my workshop confirmed it was a faulty cable connection to the glow plug control module. The repair cost was 95 Euro, which included testing and fixing the connection. The cold start was particularly problematic before the fix, and there was a noticeable improvement in engine performance after the repair. The entire process took about 2 hours at the workshop. Before suggesting more specific solutions, could you provide: Current mileage on your vehicle, When was your last routine maintenance, Are there any other warning lights or unusual engine sounds, How long has the preheating lamp been staying on, Have you noticed any engine misfire or performance issues This information would help determine if your issue is similar and whether the same solution might work for you.

Thanks for the reply. My current mileage is 97302 KM and the last service was completed 2 months ago. The preheating lamp issue started about a week ago, and vehicle stalling occurs occasionally during idle. The diesel engine also makes a slight rattling noise during cold starts, which disappears after warming up. No other warning lights besides the ones mentioned. The engine misfire seems most noticeable during acceleration, especially when the engine is cold. Going to schedule a diagnostic check to prevent any serious engine damage.

Thanks for the additional details, those symptoms sound very familiar to what I experienced. The stalling during idle and rattling noise during cold start that you mentioned are particularly telling. In my case, after the initial repair of the cable connection, the issues returned within 2 weeks. A second diagnostic test revealed that the glow control unit itself was failing, not just the connections. The control unit was corroded due to moisture intrusion, causing inconsistent preheating cycles. The complete replacement of the glow control unit cost 480 Euro, but it resolved all symptoms: No more stalling at idle, Engine light cleared, Preheating lamp functioning normally, Smoother cold start performance, Eliminated the rattling noise Based on your mileage and symptoms, particularly the cold start issues and engine misfire, I strongly suspect you are dealing with a similar glow control unit failure rather than just a connection problem. The relatively recent service suggests this is likely a component failure rather than a maintenance issue. The diagnostic test will be crucial to confirm this. Make sure they specifically check the glow plug resistance values and control unit signals during cold start conditions.

I appreciate all the detailed insights shared. After getting the diagnostic test scheduled for tomorrow morning, I wanted to follow up on the glow control unit replacement suggestion. The symptoms match exactly what you described, especially the vehicle stalling and cold start issues. Really helpful to know the approximate cost too, as 480 Euro for the control unit replacement is actually lower than I initially feared. The engine misfire during acceleration has gotten slightly worse over the past couple days, and the rattling noise during cold starts is quite concerning. Good to hear these issues were resolved completely after your repair. Will definitely ask the workshop to check both the glow plug resistance values and control unit signals as suggested. Hoping for a straightforward fix like yours. Will keep the forum updated once I get the diagnostic results and complete the repairs, as this information could help others facing similar diesel engine problems.