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Engine light

(2000 Lexus RX300)
in Melbourne, FL on December 03, 2010
The engine light stays on and the code reads
po125 closed loop fuel control insuff coolant temp
p1155 manufact control fuel air metering
p1150 ?
changeg coolant sensor and air filter
reset and check engine light comes back on after 10 miles
Displaying 4 answers & 3 comments
Popular Answer
on December 03, 2010
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.


BTW, I bet your heather isn't hot either.

on December 03, 2010
the choke reference makes sense because the idle seems very high
where is the theremosat located
on December 03, 2010
I can't post diagrams here, but if you post an e-mail I can send you some.
Also, at this point I would not worry about the air-fuel ratio sensor, the ECM will ignore its reading while in open loop mode. Get the thermostat replaced an reset the codes first, let the engine reach operating temperature, any further testing is waste of time at this point.
The sensors might be OK.

on December 03, 2010
Thanks for your quick response
E-mail adress is
on January 09, 2014
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.
of Cassels Garage on December 03, 2010
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.
on July 26, 2013
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
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