Audi A3 Diesel Glow Plug Failure Causing Smoke & Codes

Had similar issues with my 2007 Audi A4 2.0 TDI. The constant preheating lamp and smoke during acceleration pointed to a faulty preheating unit connection. The car electronics were showing error codes related to the glow plug control module. After proper diagnosis, the problem turned out to be corroded wiring connectors between the engine preheat system and the control module. The smoke was caused by incomplete combustion due to improper preheating. This is a common issue on these engines when the preheating unit loses proper contact. The fix required cleaning the connectors, replacing damaged wiring, and updating the control module software. While not the most expensive repair, it needed specialized diagnostic equipment to properly identify the failing components in the ignition system. Important: Get this checked soon, as continuous driving with faulty preheating can lead to starting problems and potential engine damage, especially in colder weather. A reputable shop with experience in VAG diesel engines should be able to diagnose this accurately. Worth noting this is typically more involved than just replacing glow plugs, as the car electronics need proper testing to ensure the preheating control system functions correctly.

Thanks for sharing that detailed experience. I had the exact same symptoms on my A3 last winter. After reading your comment, it seems we dealt with identical electrical fault issues in the preheating system. Just wondering, can you remember roughly how much you ended up paying for the complete repair? Also, has everything worked properly since the fix, or have you noticed any other related problems? This info would be really helpful since Im planning to get mine fixed soon and want to know what costs to expect with the control unit repairs.

Thanks for asking about the follow-up. After my previous message, I got the repair done and it was actually quite reasonable at 95 Euro for fixing the faulty cable connections in the heating module. The electrical fault was exactly as suspected, the preheating control unit needed attention at the connector points. The car electronics have worked flawlessly since the repair. No more check engine lights, no smoke issues, and the ignition system functions perfectly now. The preheater engages and disengages as it should, especially during cold starts. The key was finding a shop that properly diagnosed the connection issue rather than just assuming the entire control unit needed replacement. This approach saved significant costs while fully resolving the problem. Worth mentioning that regular inspection of these connections might prevent similar issues in the future, as corrosion in the car electronics can develop over time affecting the preheating system performance.

I finally took my A3 to get fixed after gathering all this helpful info. Found a diesel specialist who knew exactly what to look for with the engine preheat system. The mechanic confirmed the corroded wiring to the preheating unit was the main culprit, just like others mentioned. Total bill came to 120 Euro, slightly more than expected but included a thorough check of the entire car electronics and heating module connections. The mechanic even showed me the damaged wiring and explained how the corrosion affected the preheating control system. The car runs perfectly now, no more warning lights or smoke. Cold starts are smooth again and the preheating lamp works normally. Really glad I got proper diagnosis instead of jumping straight to replacing expensive parts. Would definitely recommend getting this checked by someone who knows these specific preheating systems. The actual fix was much simpler and cheaper than I initially feared with the faulty control module.