New member so I appreciate your time. I have the same intermittant code as others have described once every 3 or 4 weeks from a cold start. Water at good levels. Car takes a very long time to get to temp and mostly is showing low temp when this code is thrown. Seems like generally this is a the ECU sensor and/or the thermostat. Previous poster had some good pics, but also seems to be two sensors together on the top passenger side of engine by the top engine mount. Which one is the temp gauge sensor vs the ECU one? When I disconnected one to test resistance, I lose the gauge so am thinking I pulled the wrong one. Does anyone have a picture of the right one of the pair is the ECU one and the part number so I can order for my 2003 RX300. Also part number for the correct thermostat and related o-ring/gasket? Thanks

ps. one additional question. for the temp sensor, is there any thread locking sealant to be applied or just screw it in and torque to spec? For the thermostat, same question as to any sealant or is the rubber o-ring/gasket sufficient?

 

Actually i will also appreciate a picture of the sensor location on the RX300.

 

so I had the P0128 appear every few months. .. I posted above several times.... I changed the Temp Sensor over a year ago, that didn't do the trick

it was the thermostat the entire time, it was not fully closed and caused the engine to slowly warm up and never get up to full temperature

I now have a new thermostat and it warms up alot faster and temp gauge now gets up past the second marker line where it should be