Cadillac XT4 ECU Lock Mystery Stumps Dealership

I had almost the exact same issue with my 2016 XT5, also with a 2.0L gas engine. As someone with moderate experience in auto repair and car electronics, I can share what worked for me. The ECU fault and control unit errors ended up being caused by an undervoltage problem in the computer system. The workshop initially struggled to diagnose it, but after running comprehensive automotive diagnostics, they found the voltage regulator was failing intermittently. The complete fix cost me 240€, including parts and labor. The repair involved: Full diagnostic scan, Voltage regulator replacement, ECU reset and recalibration What fixed it permanently was replacing the voltage regulator and having the ECU properly reset. The fault memory lock cleared after this repair and hasnt returned in 18 months. Could you share: Current battery voltage readings? Any recent electrical modifications? Specific error codes from the ECU? Does it happen more during cold starts? This information would help determine if your issue matches what I experienced with my XT5.

Thanks for sharing your experience. Had the service last week at 35120 KM and the auto repair technician ran a full diagnostic scan. The battery showed 12.4V and error code P0562 keeps appearing. No electrical mods and yes, cold starts seem to trigger the control unit errors more frequently. The computer system shows normal readings otherwise, but the ECU fault persists despite the reset attempts. Thinking about getting a second opinion on the voltage regulator since your fix seems similar to my symptoms.

Thanks for providing those details. Looking at your readings, this definitely mirrors what I experienced with my XT5. The 12.4V reading is slightly low, mine was showing similar values before the fix. When the voltage regulator was working properly, it maintained a steady 13.8-14.2V during operation. The P0562 code (system voltage low) matches perfectly with the voltage regulator issue I encountered. The cold start sensitivity is another telltale sign, as the system requires more voltage during startup, which a failing regulator struggles to provide. After fixing my voltage regulator, the active memory started logging normal values, and the ECU fault cleared permanently. The control unit stopped throwing unusual errors, especially during those problematic cold starts. Some key points from my experience: Make sure the shop tests the charging system under load, Have them verify the ground connections, Request a complete automotive diagnostics report before and after repair, Ensure they perform a full ECU reset after fixing the regulator The symptoms align so closely that I strongly recommend having the voltage regulator checked. Better to address it now before it potentially causes more extensive electrical system damage.

Thanks everyone for the detailed responses. After comparing the symptoms and considering the P0562 code, I'm convinced the voltage regulator needs investigation. Will schedule an auto repair appointment with a shop that specializes in car electronics tomorrow. The consistency between my control unit issues and the successful fix described really helps build confidence in this approach. Good to know the ECU fault can be resolved without major expense. Will update once the voltage regulator is checked and hopefully replaced. Just to get prepared, can anyone recommend specific automotive diagnostics I should request beyond the standard ECU scan? Want to make sure they do a thorough job checking the electrical system while the memory lock issue is being addressed.