Escalade Glow Plug Control Issues + Dark Exhaust

Had the exact same symptoms on my 2020 Cadillac XT6 diesel last winter. The constant preheater activation combined with engine light and black smoke typically points to a faulty glow plug control module or compromised wiring connections. After multiple engine misfires and vehicle stalling incidents, discovered the heating element connections had corroded, causing irregular voltage distribution to the glow plugs. The car maintenance revealed both the wiring harness and control module needed replacement due to moisture damage. This is actually a serious issue that can lead to starting problems, increased fuel consumption, and potential engine damage if left unaddressed. The constant preheater operation can also drain the battery. The repair requires: Testing individual glow plug circuits, Inspecting wiring harness for corrosion, Checking control module function, Verifying proper voltage output Worth noting that while the glow plug system seems like a simple component, its malfunction can cascade into broader engine performance issues. Best to have it properly diagnosed and repaired by a shop familiar with diesel heating systems.

Thanks for sharing your experience with the XT6. Mine seems to show very similar symptoms. It just had its first engine misfire yesterday which really got me worried. Since yours was fixed, do you remember roughly how much the repair cost in total? Also curious if youve had any recurring issues with the glow plug system or engine light since the repair was done?

Good news on the repair front, got it sorted much cheaper than expected. The issue was exactly what I suspected with a defective glow control unit, but it turned out to be just a faulty cable connection that needed fixing. Total bill came to 95€ for the repair. Since the car maintenance was done, the cold start performance has been perfect. No more engine light issues or misfires with the diesel engine. The diagnostic test confirmed the glow plug system is now working exactly as it should. For the price paid, its definitely worth getting it checked professionally rather than letting it develop into a bigger problem. A proper fix prevents those frustrating cold start issues and protects other engine components from potential damage. Been about 6 months now since the repair and absolutely no recurring problems. The dark smoke issue cleared up completely too. Seems the loose connection was causing all those symptoms, and once fixed, the entire system went back to normal operation.

Finally got it checked out today and you were spot on. Took it to a different mechanic who actually specializes in diesel engines. The glow plug control unit had a loose connection causing all the trouble. Cost me 120€ for the complete fix including diagnostic work. The vehicle stalling and dark smoke issues cleared up right away after the repair. Pretty relieved it wasnt anything major like a full control unit replacement. The mechanic also did a thorough car maintenance check while it was in the shop, so feeling confident about the fix. Really glad I asked here first, saved me from possibly getting overcharged for unnecessary parts. The engine misfire hasnt happened since, and the preheater now works exactly as it should. Going to stick with this mechanic for future repairs since they clearly knew what they were dealing with.