Phaeton TDI Glow Plug Troubles & Heavy Smoke Issues

Had a similar issue with a 2007 Passat TDI. The car preheater warning light stayed on and engine light appeared, along with smoke issues. As someone with moderate experience in diesel engine maintenance, I first suspected the heating module. Took it to a workshop where they diagnosed the problem as a loose connection in the control unit wiring. The cable connecting to the preheating unit had worn out over time, causing intermittent connectivity issues. Total repair cost was 95€, which included diagnostic and fixing the connection. The symptoms you describe match what I experienced, but to provide more accurate guidance, could you share: Any error codes from diagnostics? Does the engine preheat normally in cold weather? When exactly does the smoke appear during acceleration? Have you noticed any starting issues? These details would help determine if your issue is identical to what I encountered with the wiring connection or if the preheating unit itself needs replacement. The control unit diagnosis is usually the first step before replacing more expensive components.

Latest service was done at 147200km, just a few weeks ago. Thanks for the detailed response. Got the error codes checked, P0670 and P0671. The engine struggles to start when cold and needs multiple attempts. The smoke appears right after pressing the accelerator, especially when the engine is cold. During the recent service they didnt spot any obvious electrical faults with the wiring. The car preheater warning appears instantly when starting the car, which seems to indicate a defective part in the heating module rather than just a connection issue. Given these symptoms and considering the high mileage, I am leaning towards replacing the complete unit instead of attempting smaller repairs. Would replacing the entire heating module be overkill in this case? Its a 430€ part plus labor, but might be worth it given the cold starting issues and constant warning lights.

Thanks for providing those error codes and symptoms. I can definitely help since I went through a similar progression with my Passat TDI. While my initial wiring fix worked temporarily, the issues returned after a few months. The error codes you mention (P0670/P0671) are exactly what I encountered when my preheating unit finally failed completely. The car electronics were correctly identifying a defective part in the heating module. Given your symptoms are matching mine: Multiple cold start attempts needed, Immediate preheater warning light, Smoke during cold acceleration, Clean wiring inspection I ended up replacing the complete heating module. While the 430€ cost seems high, attempting partial repairs on the preheating unit proved less effective long-term. The new module resolved all issues: Cold starts now work first time, No more warning lights, Smoke disappeared, Engine preheat functions normally Since your mileage and symptoms align with what my car experienced, I would recommend going for the complete module replacement. Trying to save money with partial fixes might lead to repeated workshop visits and continued starting problems.

Thanks for the insights from your experience. Based on your suggestion and my symptoms, I will proceed with the complete heating module replacement. The parallels between your case and mine, especially the error codes and cold starting issues, make me more confident about this decision. Since the ignition system and car electronics are showing clear signs of preheating unit failure, and considering my recent service found no wiring problems, replacing the entire module seems like the most reliable solution. While 430€ is significant, continuing to drive with a defective part could lead to more expensive problems. Will schedule the replacement next week and update once completed. Hopefully this will resolve the cold starts, warning lights, and smoke issues just as it did in your case.