Diesel Preheat Warning + Smoke = Bad Control Unit Fix

Had the same electrical fault on my 2013 Chevy Cruze diesel last winter. The heating module symptoms matched yours exactly, constant preheat light and dark smoke. The defective part turned out to be a failed glow plug control module, not just individual glow plugs. The vehicle heater diagnosis showed multiple issues: corroded connections at the module and two dead glow plugs. Car electronics were getting wrong signals, causing excessive fuel delivery and the smoke. These symptoms typically indicate a serious control unit problem rather than just basic maintenance. Quick test: If your car starts harder when cold but runs okay when warm, it's likely the glow plug system. Don't keep driving it, the unburned fuel can damage your engine over time. Got it fixed with new control module, full set of glow plugs, and proper wiring check. Completely resolved the smoke and starting issues. These car electronics problems usually need professional diagnosis with proper scanning tools. These diesel preheating issues aren't something for DIY unless you've got the right diagnostic equipment and experience with diesel systems.

Thanks for the detailed response on the diesel preheating troubles. Your symptoms and fix match my situation perfectly, actually had my Sonic checked yesterday. The ignition system scan confirmed a faulty glow plug control module just like yours. Quick question, do you remember roughly what the total repair cost was for your preheating unit replacement? And has everything stayed working properly since the fix? Was thinking about just replacing the defective part myself but your advice about needing proper diagnostics makes sense. Want to make sure I budget enough to get it done right.

Got the final repair bill from my Cruze's preheating issues, glad I could help identify the problem. My defective heating module turned out to be simpler than expected. The mechanic found a loose cable connection at the control unit that was causing all those symptoms. Only cost me 95 € to fix, way less than I initially feared. The car electronics have been working perfectly since the repair, no more warning lights or smoke issues. The vehicle heater system fires up normally now and the glow plugs are cycling correctly. Looking back, the dark smoke and constant preheat light were definitely from that bad connection messing with the ignition system timing. While DIY repairs can save money, having a proper diagnostic scan was crucial here. A faulty preheater connection can mimic more serious problems. You made the right call getting it professionally checked rather than just swapping parts hoping to fix it.

Had the mechanic look at it today and you were spot on about the diagnosis. The electrical fault turned out to be exactly what you described, a failing glow plug control module throwing off the whole ignition system. Got lucky with my repair costs though. The mechanic found that the preheating unit itself was fine, just had some corroded wiring connections causing the defective part signals. Total bill came to about €200 including diagnostics and repair work. Much better than the €800+ I was quoted for a full module replacement. Engine's running great now, no more warning lights or smoke issues. Starting up clean and smooth, even on cold mornings. Really glad I got that second opinion instead of throwing parts at it. Sometimes the simpler fix is the right one when it comes to these diesel preheating problems.