VW Transporter Glow Plug Failure Causing Smoke & Warnings

Had similar issues on my 2014 VW Crafter diesel. The constant preheating lamp combined with check engine light pointed to electrical faults in the preheating system. After troubleshooting, the root cause was a damaged wiring harness connecting to the engine preheat control module. The insulation had worn through, causing intermittent connection issues. The smoke during acceleration was typical of incomplete combustion due to improper preheating. The repair involved: Complete diagnostic scan, Testing individual glow plugs, Replacing the damaged wiring harness, Replacing the preheating unit controller, Recalibrating the heating module This was a serious electrical system issue that required specialized diagnostic equipment. Leaving it unrepaired risks further damage to the preheating system and poor engine performance, especially in cold weather. My recommendation: Have a full diagnostic performed specifically focusing on the glow plug system and preheating control module. The symptoms match classic signs of either damaged wiring or a failing preheat controller.

Thanks for sharing your experience. My VW had very similar symptoms, the preheating light stayed on and smoke was visible during acceleration. The mechanic found issues with both the preheating unit and some damaged wiring in the ignition system. The vehicle heater also needed attention since the car electronics were affected. Wondering how much you ended up paying for the full repair? Has everything worked properly since then? My repair was about 3 months ago and I want to make sure I didnt overpay, plus curious if you had any recurring issues with the defective parts they replaced.

Since getting the preheating control unit fixed, my Crafter has run perfectly with no recurring electrical faults. The repair was straightforward, just 95€ to fix a faulty cable connection in the heating module. Much simpler than initially feared. The original diagnosis pointed to multiple potential defective parts in the ignition system, but the mechanic found the root cause was just that one connection. No need to replace the entire preheating unit or other components. The smoke during acceleration completely cleared up after the repair. Three months is a good test period, if you havent seen any warning lights or symptoms return, the repair was likely done correctly. The engine preheat system is pretty reliable once properly fixed.

Thanks for the feedback. After visiting my mechanic last week, the final bill came to 780€. This included replacing the preheating unit and repairing damaged wiring in the vehicle heater system. Initially worried it would cost more given all the electrical fault symptoms. The vehicle runs perfectly now, no more smoke during acceleration and the warning lights have stayed off. The engine preheat system works as it should, especially noticeable on cold mornings. Really glad I addressed this before winter. Looking back, I was right to be cautious about questionable repairs. The mechanic showed me the defective parts they removed and explained exactly what was causing the issues. Having detailed documentation of the work done gives me peace of mind that it was a legitimate fix. Just wanted to close this thread and confirm everything worked out. The repair cost seems fair based on what others paid for similar issues.