CT6 Power Loss Points to ECU Mystery, Owners Seek Truth

Had a similar situation with my 2020 CT5 last summer. Initially, diagnostic scan pointed to ECU failure, but the actual problem turned out to be a defective main relay causing intermittent power loss to the vehicle electronics. The symptoms matched exactly, unusual power loss, multiple error codes, and inconsistent engine performance. The computer module would reset itself occasionally, making the problem appear ECU-related. The fix required testing the entire circuit and power supply to the ECU first. A proper automotive electronics diagnostic revealed the main relay was failing to maintain consistent power to the system. After replacing the main relay and performing a system reset, all issues were resolved. This was not a serious repair compared to a full ECU replacement. The key is having a thorough diagnostic process before jumping to expensive component replacements. ECU failure is relatively rare unless there has been water damage or severe electrical issues. Worth getting a second opinion from a shop specializing in vehicle electronics and ECU repair before approving major work.

Thanks for sharing your experience. I ran into almost identical symptoms with my Cadillac a while back. The automotive electronics diagnosis initially suggested an ECU problem, but my root cause ended up being quite different, corroded wiring harness connections that were disrupting the engine control signals. Would you mind sharing what the relay repair ended up costing you? And have you had any issues with the control system since the fix? Just trying to compare notes since these electrical gremlins can be tricky to diagnose correctly.

After seeing the mechanic who properly diagnosed the issue, I am happy to report the engine control unit is working perfectly now. The repair was straightforward, replacing the defective main relay resolved all the power loss and error code problems. Total cost was 120€ for parts and labor, which was a huge relief compared to a full ECU replacement. The car diagnostics have been clean ever since, with no recurring issues in the automotive electronics or control systems. The system reset after the relay replacement cleared all error codes permanently. This experience really shows how important thorough testing is before replacing expensive components like the ECU. After 6 months of trouble-free driving, I am confident the faulty relay was the true culprit. The computer module is functioning exactly as it should, with consistent power delivery and no more unusual shutdowns.

Thanks everyone for the helpful feedback. After getting a second opinion from a different mechanic specializing in automotive electronics, it turned out my issue was actually a corroded ground wire connection causing intermittent power problems. The loose connection was making the engine control system act erratically and throw multiple error codes. The repair was much simpler and cheaper than a full ECU replacement, just 200€ for cleaning the connection points, replacing the damaged wiring section, and running a complete system reset on the car diagnostics. Engine performance returned to normal immediately after the fix. Been driving for about 3 weeks now with zero issues. No more power loss, no error codes, and the engine control is working perfectly. Really glad I questioned the initial diagnosis and got that second opinion before paying for an expensive ECU replacement I didnt actually need.