the ECU thinks everything is good. I've seen people wire in a resistor near the ECU and cut the plug under the hood. Look for any electrical tape or modification near the ECU plug. Do you have safety boost? Honestly if all is good and you have no safety boost then I wouldn't worry. Those Det sensors are nothing but trouble anyway. Just leave it be and run high octane gas and you should have no issue. Don't fix what isn't broke!