Cadillac CT6 Hybrid ECU Failure Halts Engine Start

Had this exact situation with a 2016 Cadillac CT5 Hybrid. Initially, the check engine light came on and engine diagnostics pointed to an ECU issue. However, after thorough testing, it turned out the battery cables had corrosion and loose connections. The symptoms matched perfectly, no start, complete electrical system shutdown, and misleading engine fault codes. The ECU was reporting errors because it wasnt getting consistent power supply. The fix required cleaning the battery terminals, replacing the corroded cables, and resetting the engine software. After addressing these connection issues, all error codes cleared and the car started normally. This is a relatively straightforward fix but can be serious if left unattended, as poor connections can damage the ECU and other electrical components over time. Would recommend checking these basic electrical connections before diving into more complex fuel injection diagnostics. Getting a second opinion from another certified mechanic might help confirm whether your issue stems from actual ECU problems or just poor battery connections.

Thanks for sharing your experience. My CT6 had very similar symptoms last year. The engine fault codes also indicated ECU failure initially, but my situation turned out to be a damaged wiring harness that was causing intermittent connection issues. Did you remember roughly how much the repair ended up costing? Also curious if youve had any related electrical problems since getting it fixed.

Recently took it back to the mechanic and glad to report the engine control malfunction is completely resolved. The total repair came to 155€ for cleaning and replacing the faulty battery cable connections. Since fixing those connections, the car has been running perfectly with no engine fault codes or ECU issues. The engine diagnostics are all clear now and the electrical system is working as it should. This really confirms what many CT6 owners discover, what appears as complex engine software problems often traces back to basic electrical connections. No electrical problems whatsoever in the months following the repair. The engine surge issues that appeared initially have completely disappeared. Would strongly recommend having your wiring harness thoroughly inspected, as poor connections can trigger misleading error codes.

After waiting three days for an appointment, I finally took the car to my regular mechanic. Just like you mentioned, the actual problem was much simpler than expected. The mechanic found significant corrosion on multiple wiring connections, causing the ECU failure warnings. The total repair cost was 280€, which included a complete electrical system inspection, cleaning all connections, and replacing two damaged wiring sections. They also performed a full engine diagnostic scan to ensure no other issues were present. The car now starts perfectly, with no check engine lights or error codes showing up. The fuel injection system is working normally, and the engine surge issues I was worried about turned out to be just symptoms of the bad connections. Really glad I got this fixed before it could cause any permanent damage to the ECU.