VW Sharan Diesel: Glow Plug Control System Failure Alert

I had a similar issue with my 2015 VW Touran diesel engine. With some experience working on VW diesels, I can relate to these symptoms, especially the cold start problems. The engine light and preheating lamp combination often points to electrical issues in the glow plug system. In my case, the diagnostic test revealed a loose connection in the wiring harness connecting to the glow plug control module. The symptoms were identical, persistent preheating lamp, engine light activation, and smoke during acceleration. The repair was straightforward once properly diagnosed. The workshop found corroded terminals and a damaged cable insulation causing intermittent connections. Total repair cost was 95€, which included cleaning the connections and replacing the damaged wiring section. Before suggesting specific solutions, could you provide: Current mileage, Any recent car maintenance work, Whether the smoke is black or blue, If the problems occur more during cold start, Any engine performance changes This information would help determine if your issue matches what I experienced or if there might be other underlying problems. Keep in mind that while a faulty glow control unit is possible, its always worth checking the simpler electrical connections first. Modern diesel engines are sensitive to poor electrical connections in the glow plug system.

UPDATE: After some basic troubleshooting at 14955km, I can provide more details from my last regular service. The smoke appears black rather than blue, and yes, issues are definitely worse during cold starts. The engine performance drops noticeably, especially when accelerating from a stop. The glow plug warning behavior matches exactly what you described with your Touran, staying lit continuously instead of the normal brief illumination during startup. Did your repair require any special diagnostic equipment? Also wondering if your workshop mentioned potential damage to the heating elements in the glow plugs themselves during their inspection.

Thanks for the detailed update. Your symptoms mirror my Touran situation even more closely now that you mention the black smoke and cold start issues. The workshop did use specialized diagnostic test equipment to check the glow plug system thoroughly. While the wiring was the main culprit in my case, they actually found one faulty glow plug with a damaged heating element during testing. For reference, my issues started around 145000km, quite similar to your mileage. The black smoke during acceleration combined with poor cold start performance strongly suggests incomplete combustion, which matches the symptoms of a compromised glow plug system. The total repair ended up slightly higher than initially quoted, 180€ including: Full diagnostic scan, Wiring harness repair, Replacement of one glow plug The workshop checked all four glow plugs individually, which I recommend in your case. Even if the control unit or wiring is the primary issue, extended running with electrical problems can damage the heating elements in the plugs themselves. Have you noticed if the engine seems louder than usual during cold starts? This was another symptom I experienced that helped confirm the diagnosis.

Thanks for such thorough input about the diagnostic test findings. The cold start noise issue you mentioned is definitely present in my case too, there's a distinct rattling sound for the first minute or so of operation. I scheduled a workshop visit for next week. Based on your experience, I requested they perform a complete glow plug system inspection, including individual heating element testing. The similar mileage and identical symptoms make me confident we're dealing with the same root cause. My vehicle service history shows no glow plug system work ever being done, so addressing this at 145000km seems reasonable. The estimated 180€ repair cost actually sounds quite fair for the level of diagnostic work and potential parts needed. One final question before my appointment, did you notice any improvement in fuel consumption after the repair? My fuel economy has gradually worsened over the past months, which I now suspect might be related to this vehicle stalling issue during cold starts.