VW Lupo Diesel Glow Plug Failure Symptoms & Fix Tips

Using a 2004 VW Polo TDI, I encountered nearly identical symptoms. The constant preheating lamp combined with check engine illumination pointed directly to faulty connections in the preheating unit wiring harness. After inspection, the car electronics showed multiple error codes related to the glow plug control module. The smoke during acceleration typically occurs when the engine preheat cycle fails to complete properly, causing incomplete combustion. The root cause was corroded terminals at the main connector block of the preheating control unit. The repair involved: 1. Complete removal of the vehicle heater control module 2. Cleaning all connector terminals 3. Replacing damaged wiring segments 4. Installing new connector blocks 5. Recalibrating the preheating unit This was a serious electrical system issue that required specialized diagnostic equipment. Left unaddressed, it could have led to starting problems and potential engine damage, especially in cold weather. The repair took about 4 hours of labor, and I recommend having it done by a shop familiar with diesel preheating systems. The smoke issue disappeared completely after the repair, and the warning lights have not returned since.

Thanks for sharing your Polo experience. My Lupo had similar symptoms last winter, and the defective part turned out to be the preheating control unit too. The vehicle heater system needed a complete overhaul. The engine preheat warning was a clear sign something was wrong. Can you remember the total cost for your repair? Just curious to compare since prices vary quite a bit. Also, have you noticed any other electrical issues since the fix? My car runs perfectly now but always good to know what to watch out for.

Had my vehicle checked by a certified technician last week and they confirmed the preheating control unit was indeed defective. The repair bill came to 95€, which covered fixing a faulty cable connection. The electrical fault was simpler than initially expected, just a loose plug connection to the control unit that needed proper securing. Since the repair, the ignition system works flawlessly. No more warning lights or smoke issues. The engine starts perfectly even on cold mornings, suggesting the preheating unit is functioning as intended. Unlike some cases where multiple defective parts need replacement, this turned out to be a straightforward fix. The initial symptoms matched yours exactly, and having it properly diagnosed saved both time and money. Worth noting that regular checks of the electrical connections can prevent similar issues from developing in the future.

Thanks for the input. I finally got the repair done last week. The mechanic found the preheating control unit needed replacement due to water damage. Total cost was 420€ including parts and labor. Much better experience than my previous mechanic attempts. This shop used proper diagnostic equipment to pinpoint the electrical fault in the engine preheat system. They also checked the entire preheating unit for other potential issues. The car starts perfectly now, no more warning lights or smoke. Really glad I asked here first, helped me understand what to expect and not get overcharged. The vehicle heater system works great now, especially during cold starts. Only took half a day to fix, and they even showed me the damaged parts. Getting it done by specialists who know diesel systems was definitely worth it. No other electrical issues since the repair.