Hi there, I have an 02 Corolla 1zz-fe engine with a 5 speed manual with 195,000km. It started throwing a p0125 code recently, did some research and asked around, and got told the most common causes are the thermostat being stuck open/faulty or the ect sensor. I replaced both and the code came right back on the first test drive. I also know it has a faulty upstream (bank 1 sensor 1) 02 sensor. Could that be causing it? Coolant is topped off and has been properly bled since both of these jobs were done.
It appears on some models, Toyota doesn't adhere to the standard definition for DTC P0125 which is related to the ECT.
Hopefully this video will help diagnose the issue.
Service manual info:
Non-Oxygen sensor won't do that. If you use known good parts. OEM thermostat OEM coolant temperature sensor then you either have a wiring system problem or the main computer has a flaw and reads the temperature wrong
@scottykilmer I used a NAPA thermostat and a Lordco which is an Auto Parts store up here in Canada ECT sensor. Should I try OEM ones from Toyota and see if it fixes it? The thermostat was replaced once before I just did it and still threw the code with the old one as well once it was about six or seven years old. I have no previous record of the ECT sensor being replaced.