Touareg Diesel: Black Smoke + Stuck Preheat Warning

When my VW Phaeton V6 TDI 2008 showed identical symptoms, the diagnostic test revealed faulty connections at the glow plug control module. The heating element in one plug had completely failed, causing incomplete diesel combustion and the dark smoke during acceleration. The vehicle stalling and constant preheating lamp were clear indicators of glow plug system issues. After proper diagnosis, we found corroded wiring harness connections and one failed glow plug. Car maintenance records showed no previous glow plug replacements, which explained the wear. This was a serious issue requiring immediate attention since cold starts became increasingly difficult and engine performance was compromised. The fix involved replacing the entire glow plug set and control module, plus repairing the wiring connections. The engine light cleared after repairs and the exhaust returned to normal. Based on your symptoms, I strongly suggest having a specialized diagnostic test focusing on the glow plug system. The similar age and mileage of these VW diesel engines often show these issues, particularly with the preheating system.

Thanks for sharing your experience. Your Phaeton situation sounds identical to what Im dealing with. After reading about the glow plug system issues I feel more confident about whats wrong. The constant preheating lamp and engine light match exactly whats happening with my Touareg. Do you remember roughly how much you paid for the complete repair? Also curious if you had any related issues pop up since the fix? Im planning to take it to a shop this week for a proper diagnostic test of the glow plug system but want to have a ballpark figure in mind.

Thanks for asking about the costs. After getting it checked by the mechanic, it turned out to be simpler than my initial repair. The diagnostic test confirmed a defective glow control unit, but unlike my previous case, only the cable connection needed fixing rather than a full replacement. The total repair came to 95€, which covered fixing the faulty wiring connection to the glow control unit. This resolved both the constant preheating lamp and engine light issues. The diesel engine now starts perfectly, even during cold starts, with no more dark smoke from the exhaust. Since this repair six months ago, the engine misfire symptoms have completely disappeared and everything works as it should. The quick fix prevented any potential damage to the glow plugs themselves, which would have been much more expensive to replace. Your Touareg might have a similar simple fix, but definitely get that diagnostic test to be certain. Sometimes these glow plug system issues can be resolved without major component replacements.

I took my Touareg to the mechanic yesterday after getting your advice. The diagnostic test confirmed exactly what you suggested, a faulty connection in the glow plug system. The mechanic found corroded wiring at the control unit, similar to what you described. Total repair cost came to 180€, which included the diagnostic test, cleaning the connections, and replacing one damaged wire. The car maintenance was completed in about 2 hours. My diesel engine now starts perfectly, even during cold starts this morning. The preheating lamp and engine light are both off, and the dark smoke during acceleration has completely disappeared. The mechanic mentioned this is a common issue with these models and recommended checking the glow plug system during future services to prevent similar problems. Really glad I asked here first, saved me from potentially expensive unnecessary repairs at the first shop that seemed unsure about the issue.