VW Passat TDI Glow Plug & Preheat Warning Issues

As someone with moderate DIY experience, I dealt with an identical issue on my 2020 VW Golf TDI. The symptoms you describe match exactly what I experienced, persistent glow plug warning, check engine light, and that annoying rough idle during cold starts. My diagnostic scan revealed issues with the glow plug system. The workshop found one faulty glow plug that was causing the entire system to misfire. The total repair cost was 440€, including parts and labor. The job took about 3 hours since they had to test each glow plug individually to identify the problematic one. The rough idle completely disappeared after the repair, and the engine light hasnt returned in the 8 months since. Cold starts are now smooth and quick, just like when the car was new. Before offering more specific advice, could you share: Current mileage on your Passat, Whether youve noticed any smoke from the exhaust, If the diesel engine makes any unusual sounds during startup, When was your last major service These details would help determine if your issue is isolated to the glow plugs or if there might be related problems that need attention.

Thanks for the detailed feedback on your Golf experience. My Passat just had its annual service last month and currently shows 92655km on the odometer. The exhaust shows normal white vapor during cold starts, but no excessive smoke. Apart from the rough idle, I havent noticed any unusual engine sounds during startup. The engine combustion feels uneven only during the first minute of operation. After reading about your repair cost and timeline, I am thinking about getting all glow plugs replaced at once to prevent future issues. Would you recommend this preventive approach, or should I just replace the faulty one if found?

Based on your mileage and symptoms, replacing just the faulty glow plug should be sufficient. On my Golf, I initially considered replacing all glow plugs too, but the mechanic advised against it since modern diesel car glow plugs typically last well beyond 150000km when properly maintained. The cold start symptoms you describe, normal white vapor and brief uneven engine combustion, match what I experienced before the repair. Since your annual service was recent and no other issues were flagged, this suggests an isolated glow plug failure rather than a systemic problem. The diagnostic and repair process should be similar to what I went through. Make sure they perform individual testing of each glow plug to pinpoint the exact failing unit. Going this route instead of full replacement will save you roughly 300€ while still resolving the engine misfire and warning light issues. If youre keeping maintenance records, expect the single glow plug replacement to hold up well. My Golf has gone through two winters since the repair with perfect cold starts and no engine light recurrence.

Thanks for clarifying about your glow plug experience. After hearing about your Golf repair and considering my Passats fairly low mileage, I think Ill follow your advice and just replace the faulty glow plug instead of doing a complete set replacement. The engine combustion issues during cold starts match exactly what you described, so Im feeling more confident this is the right diagnosis. Given that my car just had its service and the mechanic didnt flag any other issues, tackling just the problematic glow plug makes the most sense, especially with that 300€ savings you mentioned. Ill make sure the workshop does individual glow plug testing to find the exact failing unit. Really helpful to know your repair has lasted through multiple winters without any rough idle or engine light problems returning. Will book the appointment this week and hopefully get this sorted quickly.