Alfa Romeo Stelvio Preheater Failure Causes Smoke & Heat Loss

Had the exact same symptoms on a 2018 Alfa Romeo Giulia diesel. The persistent engine preheat light combined with smoke pointed to a defective heating module. Initial diagnosis revealed an electrical fault in the glow plug wiring harness. The root cause was a damaged cable connection where the wiring meets the heating module. Corrosion had built up on the connectors, creating resistance and preventing proper voltage flow to the glow plugs. This explained both the smoke during acceleration and heating issues. This is a serious problem that can lead to starting difficulties and potential engine damage if left unaddressed. The car electronics need thorough testing to pinpoint exactly which part of the preheater system has failed. In my case, the defective part was the wiring harness connector, not the entire heating module as initially suspected. The repair involved cleaning the corroded connections, replacing the damaged section of the harness, and testing the glow plug resistance values. After repair, both the preheat warning and check engine lights cleared, and proper engine preheat function was restored. Would recommend getting this checked soon, as continued driving with faulty glow plugs can cause fuel efficiency issues and potential engine wear.

Thanks for the detailed write-up on your preheater issues. Running into similar problems with my 2016 Alfa Romeo Stelvio right now, preheating unit acting up and smoking under acceleration. Your description of the electrical fault with the wiring harness matches what my mechanic suspects too. Curious to know how much the repair ended up costing you? Also wondering if the control unit has given you any more trouble since the fix? Considering whether to just replace the entire system while its being worked on to prevent future issues.

Just had the repair completed last week. Like suspected, the preheating control unit was defective due to a faulty cable connection. The car electronics diagnostic confirmed it was just the wiring connection causing the issue, not the entire heating module. Total repair cost came to 95 Euro, which covered fixing the defective part and labor. Much better than replacing the whole preheater system unnecessarily. Since the repair, everything works perfectly, no more warning lights, smoke issues are gone, and the engine preheat function operates normally. My advice would be to start with repairing the existing components before considering a full system replacement. Often these issues stem from simple connection problems rather than complete unit failure. The key is getting an accurate diagnosis of the car electronics to identify the exact point of failure in the preheating system.

After getting your feedback, I finally took my car to the mechanic last Thursday. The ignition system diagnosis confirmed what you mentioned, it was indeed the wiring harness causing the preheater malfunction. The mechanic found significant corrosion at the connection points of the heating module. The repair was straightforward and cost 120 Euro total, slightly more than yours but still reasonable. They cleaned all connections, replaced the damaged wiring section, and tested the entire car electronics system. The defective part was just the wiring, so thankfully no need for a complete heating module replacement. Started right up after the fix, no more smoke, warning lights are off, and the engine preheat works perfectly now. Really glad I caught this early before it could cause more serious issues. Thanks again for sharing your experience, helped me avoid an unnecessary complete system replacement.