Meetya

I hope this will help a lot of people doing search on this forum.

Short: If you get P0125, the heater of one of your top O2 sensors (before catalytic converters) is failing. It has nothing to do with the coolant temperature. I will post info on how to check them in the next post (I need to attach a second file).

Long (see attached PDFs):
"To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three-way catalytic converter is used, but for the most efficient use of the three-way catalytic converter, the air-fuel ratio must be precisely controlled so that it is always close to the stoichiometric air-fuel ratio.
* approximately proportional to the existing The A/F sensor has the characteristic that provides output voltage
* is used to provide feedback for the ECM to control the air-fuel air-fuel ratio. The A/F sensor output voltage ratio.
By the A/F sensor output, the ECM can determine the deviation amount from the stoichiometric air-fuel ratio and control the proper injection time immediately. If the A/F sensor is malfunctioning, ECM is unable to perform accurate air-fuel ratio control.
The A/F sensor is equipped with a heater which heats the zirconia element. The heater is controlled by the ECM. When the intake air volume is low (the temp. of the exhaust gas is low), current flows to the heater to heat the sensor for accurate oxygen concentration detection.
*: The voltage value changes at the inside of the ECM only."

Meetya

Here is how to check the heaters (see attached PDF):
- Disconnect the A/F sensor connector.
- Using an ohmmeter measure the resistance between terminals +B and HT (they are silver).
- Resistance: 0.8 - 1.4 Ohm at 20C (68F)
- If the resistance is not as specified, replace the sensor.
- Torque: 44 N·m (440 kgf·cm, 31 ft·lbf)
- Reconnect the A/F sensor connector.

Lexmex

I have posted previously here, https://www.clublexus.com/forums/sho...ighlight=p0125

P0125 (Insufficient Coolant Temperature for Close Loop Fuel Control)

DTC Detecting Condition:

After the engine is warmed up, A/F sensor output* does not change when conditions (a), (b) and (c) continue for at least 1.5 minutes.
*: The output value changes at the inside of the ECM only.
(a) Engine speed: 1,500 rpm or more
(b) Vehicle speed: 40~100 km/h (25-62 mph)
(c) Throttle valve does not fully close

Trouble Area:
-Open or short in A/F sensor circuit (bank 1, 2 sensor 1)
-A/F sensor (bank 1, 2 sensor 1)
-ECM

Meetya

Good. Just trying to post useful posts :-)

Lexmex

I think the error itself is just very strange in that it says something using coolant temperature, but in the end A/F sensors are the key factor in play. I think there is another error on the RX that relates to the active shock mounts and the exhaust, actually a DTC condition. You would think when the names of these OBD2 codes were developed, the name would have a little more to do with the type of error.