The way that I read it is that PO125 code is set when a lean condition in recorded and the mil light will come on. This information is on a 2000 toyota camry. They want you to check the heated oxygen sensor to make sure the heated oxygen sensor is not bad and working properly and not stuck in a lean condition and causing the code. If it is good then the lean condition is caused by something else up the line. They also say that PO125 is set when it runs out of gas causing the lean condition. This is from a non california car. I don't know what year you are working on. Maybe what you are working on is saying that the ECT is not up to temperature and you don't have heated oxygen sensors and it is running in open loop because of it. Just my worth.
Oxygen sensor failures are common to all cars not just Toyotas. But Toyotas present different codes that you might not expect for this common problem.
When a car has the 300 dollar oxygen sensor (California emissions) we call it the air fuel ratio sensor. Check with Toyota dealer by VIN number to verify which type you have. An air fuel ratio sensor is not interchangeable with a regular oxygen sensor even though they look the same.
P0171 System Too Lean. This code will set when an air fuel ratio sensor gets lazy.
P0125 Insufficient Coolant Temperature For Closed Loop. Sounds like a bad thermostat right? No, on Toyotas its our air fuel ratio sensor taking too long to get active.
P1135 Air Fuel Ratio Sensor (Bank 1 Sensor 1) Heater Circuit Malfunction. The heater in the air fuel ratio sensor is drawing too much or too little current.
Amazon sells the Bosch 13733 air fuel ratio sensor for about 113 dollars which is the lowest price I have been able to find anywhere. This sensor works well on