Check Engine Light

[zamata]

I have a 2000 GS300 at around 50K. Recently the check engine light

came on. Went off for a day but back on today.

Pulled the code and it says P0125 "Clsd Loop Fuel Ctrl: Insufficient Coolant Temp"

Everything on the car seems OK. No noticeable changes including the temperature.

Had used lower octane gas in the past.

I had searched the forum for P0125 related posts but none deal with the

lower octane gas as a possible cause.

[GuyTelefunken]

This code is rather complicated. It has to do with the oxygen sensors not reporting correct readings after the engine has reached operating temperature. Since the code seems to point specifically to coolant temperature, I would tend to look at the readings from the coolant temperature sensor with a scantool capable of displaying real-time data. You need to read the temperature from the sensor using the scantool for an accurate reading other than that which is displayed on the dash gauge.

As this code also points to one or more of the oxygen sensors not reporting a change from lean to rich after warm up specifications have been met, it is also likely that an oxygen sensor has failed. If you have considerable mileage on your GS (>50K) it is quite likely that an oxygen sensor is the cause. Keep in mind that an oxygen sensor can fail at any mileage. If you can read the data from the sensors (preferably using a graphing scantool) it will be easy to see if one or more is reporting vastly different readings from the others.

If you don't have repair experience in this area, I'd recommend a reputable shop to diagnose this.