Scotty I have 2001 Corolla LE Automatic transmission with with over 145,500 miles. A few weeks ago the check engine light came on, so I made a check with my OBD2 scanner and get a P0125 code. I replace the ECT sensor and the fuel economy came back up with no engine check light, but after a week of driving, the check engine light came back on. I check the code and it P0125 again. every now and then there will be no engine check light on for a few days or a week and then it will just come back. What possible can cause a P0125 code to popup again after installing a new ECT sensor? it not over heating, coolant is top off. I am lost and getting frustrated. I hate to see a check engine light on.
It could be the thermostat. Check the thermostat to ensure it is opening properly. Use a voltage meter or infrared thermometer to continue diagnosing the problem. It could be within the wiring or the computer, or mabey a coolant leak. Check both the radiator and the overfill tank when the car is cool. Also check the coolant system for leaks of bad wiring. But don't ignore this, as it may prevent future problems. Hope that helps.
Thanks I will try that, but there is no coolant leak.
OK I remove the new aftermarket ECT sensor, and install a new OEM thermostat, and a new OEM ECT sensor, but the check engine light stay off for a few minutes. As soon as I get on the highway the the check engine light came back on. I use the scan tool and it show P0125 still. I no not know what else to try. I had even change to old coolant and add new coolant was.