VW Passat: Glow Plug Issues Cause Starting Problems

I had a very similar issue with my 2019 VW Golf TDI diesel engine. The symptoms were nearly identical, engine light on, difficult cold start, and preheating lamp issues. After multiple attempts to start the car on cold mornings, I knew something was wrong. A diagnostic test revealed it was indeed a faulty connection in the glow plug control module wiring harness. The cable connection had corroded over time, causing intermittent contact issues. The repair cost was 95€, which included testing and replacing the damaged wiring. The vehicle stalling and smoke issues completely disappeared after the fix. The workshop explained that bad connections in the glow plug system can cause incomplete combustion, especially during cold starts. What trim level is your Passat, and how many kilometers has it done? Also, are you noticing any specific patterns with the starting issues, worse in cold weather or after the car sits for several days? These details could help confirm if your issue matches what I experienced. Definitely recommend getting it checked soon, as driving with glow plug system issues can potentially cause more serious engine problems over time.

I agree with similar symptoms described. My Passat has 138197km and had its last service 3 months ago. Had some work done on the fuel system but this feels different. The cold start issues are most noticeable after the car sits overnight, even in mild weather. The engine light came on suddenly last week, and smoke appears mainly during initial acceleration. The glow plug warning behavior started around the same time. Called the workshop and they suggested checking the control unit first before replacing individual glow plugs. Makes sense given the multiple warning lights and consistent preheating lamp issue. Will get it diagnosed this week and share what they find. For now, I noticed letting the glow plugs heat a bit longer before starting helps somewhat, but clearly need proper car maintenance to resolve this.

As mentioned in my previous reply about my Golf TDI, letting the glow plugs heat longer was also my temporary workaround, but it really just masked the underlying issue. Your symptoms align perfectly with what I experienced, especially the smoke during acceleration and persistent warning lights. The fact that your issues started suddenly after recent fuel system work is interesting. When my control unit failed, it also happened quite abruptly. The diesel engine diagnostic test showed the heating element timing was completely off, causing poor combustion and those exact smoke patterns you described. Your mileage is quite close to when my problem occurred (I was at around 145000km). The workshop will likely start by testing the control unit and checking the glow plug circuits. In my case, they initially suspected individual glow plugs but found the control unit was the root cause. Based on my experience, if they confirm it is the control unit, requesting a complete system check including the wiring harness connections would be wise. Sometimes corrosion affects multiple components in the glow plug system. Let us know what the diagnostic test reveals. Would be useful to confirm if these control unit issues are becoming a common pattern in our engine type.

Thanks for the detailed feedback regarding the Golf TDI experience. The workshop confirmed my suspicions today, faulty glow plug control unit causing the engine misfire and cold start problems. The diagnostic test revealed erratic voltage readings across all four glow plugs. Total repair estimate is 380€ including parts and labor. They recommend replacing both the control unit and wiring harness since they found some corrosion near the connections. Makes sense given the multiple warning lights and consistent preheating issues. The technician mentioned these problems are fairly common at this mileage. Vehicle stalling during cold starts can damage other components if left unchecked, so getting it fixed this week. Good call on suggesting the full system inspection, they found a cracked insulation sleeve that could have caused more issues later. Will update once the repair is complete. The smoke during acceleration and engine light warnings have been concerning, but at least now I know exactly what needs fixing. Just hoping no additional problems surface during the repair.