Audi Q5 Glow Plug Failure Causing Smoke and Warnings

As an A4 2.0 TDI (2012) owner, I encountered nearly identical symptoms last winter. The constant preheating lamp combined with engine light typically indicates issues with the car preheater system. In my case, the problem was traced to corroded cable connections at the preheating unit, causing intermittent contact. The smoke under acceleration often occurs when the ignition system isnt functioning properly due to faulty preheating. The defective part was actually the wiring harness connecting to the glow plugs, not the glow plugs themselves. The car electronics were sending correct signals, but the connection was compromised. Key points to discuss with your mechanic: Have them check the wiring harness for the preheating unit, Request testing of individual glow plug circuits, Ask for inspection of the control module connections, Get verification of the glow plug resistance values This is generally a serious issue that should be addressed promptly, as continued operation can lead to starting problems and potential engine damage. These symptoms almost always indicate a hardware problem rather than just sensor errors.

Thanks for the detailed response about the preheating unit issue. Our symptoms do sound very similar. The vehicle heater problems started causing trouble during cold starts too. The mechanic ended up replacing both the wiring harness and two glow plugs. Curious, do you remember roughly what you paid for the repair? Also, has your engine preheat system been working reliably since the fix? I noticed my car electronics are showing some other minor warnings now, wondering if they might be related.

Good to follow up on your preheating unit concerns. Finally got my repair bill details, it came to 95 Euro for fixing the faulty cable connections. Much better value than replacing the entire control unit, which was initially suggested. The electrical fault turned out to be a simple connection issue in the preheating system. Since the repair, the engine preheat works perfectly, no more warning lights or cold start problems. If your car electronics are still showing other warnings, they might need separate diagnosis. A defective control unit can sometimes trigger multiple alerts, but since your mechanic already replaced the wiring harness and glow plugs, those new warnings are probably unrelated. The ignition system issues completely cleared up after the repair in my case. Make sure your mechanic confirmed all connections are properly sealed, moisture in these connections is often what causes the initial problem.

Thanks for the advice. After checking all the recommended points, I took my Q5 to a different mechanic who specializes in car electronics. The heating module turned out to be fine, but they found corrosion affecting the preheating unit connections, just as suggested. The repair cost 280 Euro including new wiring and labor. They also cleaned the existing connectors and applied protective coating. The car is running perfectly now, no more smoke, warning lights are gone, and the preheater works normally in cold weather. The other electrical warnings disappeared too once they fixed the main issue. Really glad I got a second opinion instead of replacing the entire system. The entire car electronics system seems much more stable now. Definitely learned to pay more attention to maintenance of the preheating system, especially checking for moisture damage around the connections.