2000 Lexus RX300 Q&A
2000 Lexus RX300 Question: engine light
Replace the thermostat, reset the ECM and drive it. If the engine won't reach operating temperature due to a stuck open thermostat, the ECM won't switch to "Closed Loop" mode, also keep dumping fuel into the combustion chamber. It's kind of the same than driving a carbureted vehicle with the choke on all the times. I think the ECT sensor was OK, it was taking the correct (low temperature) reading, it's actually the thermostat that failed. Zee BTW, I bet your heather isn't hot either. - ZeeTech
All these codes retain to the air/fuel ratio sensors. More commonly called an oxygen sensor. The vehicle has 4 of them. It is more often the front sensor(s) or position 1. There are methods of testing so that you don't have to buy more parts than necessary. - Cassels
the problem is your oxygen sensors i just replaced both on a lexus rx300 and it got rid of the poi125 p1150 and p1155 i done the thermostat first and it didnt fix the problem - z28man28
P0125 indicates that the engine takes too long to warm up to the minimum closed loop operating temperature which is generally around 170 degrees F. This is almost always caused by a "lazy" thermostat that is stuck open or opens too easily. Replace the thermostat with one that is OEM spec, clear the codes and this will solve the P0125 issues. The P1155 is an air fuel ratio sensor heater problem on bank 2 sensor 1 (this is the cylinder bank that is opposite the bank that has the number 1 cylinder) check the resistance of the heater element in the sensor and if out of spec, replace the A/F sensor, however, please verify that you have a good 12 volt signal to the heater circuit at the proper time before you condemn the sensor. An inexpensive OBD-II scanner will help see this. Hope that this helps. - dandd
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