P0131 Front 02 sensor low (lean)
En HDForums dicen que puede ser una entrada de aire por la unión del mismo al cilindro. Por lo visto el sensor de oxígeno lo detecta y marca el error. O inyector obstruido.
Te lo pongo todo:
A "Lean O2 Sensor" Code does not necessarily mean that the mixture is actually "Lean".. Remember that the name of the sensor is the "Oxygen Sensor" NOT the Mixture Sensor. Therefore; anything that might cause a lot of Oxygen in the exhaust will generate the conditions that are required for the ECU (Computer) to set a "Lean O2 Sensor" code.
So, what might these be?
1.) The Mixture really might be lean. A bad or plugged Fuel Injector for that cylinder would be the most probably cause if the mixture really is Lean. If it were anything else the problem would either be occuring with both cylinders or your idle speed would be really high.
2.) Any sort of a misfire will increase the amount of Oxygen in the exhaust. The misfire can be caused by either a fuel or an ignition problem; it doesn't matter. Remember that the Oxygen Sensor is only measuring Oxygen; so even though a misfire may be dumping a lot of raw fuel into the exhaust the Oxygen Sensor doesn't measure fuel. A misfire will not use any fuel and it will not use any Oxygen either. So a misfire (no matter what the reason) will look like a Lean Mixture to the Oxygen Sensor because the Oxygen content of the exhaust will ALWAYS increase when there is a misfire!
3.) An exhaust leak between the Cylinder Head and where the Oxygen Sensor is located in the Exhaust Pipe. The leak doesn't have to be very big to cause a lot of headaches. You may not even hear it! While it is true that there is a high pressure shock wave that travels down the exhaust pipe every time the Exhaust Valve opens . . . what is also true is that between each of these High Pressure Shock waves is a Low Pressure wave. This is part of the principle that a Header
Exhaust System uses to increase the performance of an engine. Anyhow, when the Low Pressure Wave passes a leak it will draw outside air into the exhaust pipe and the Oxygen Sensor will interpret this as a lean mixture.
4.) An Oxygen Sensor that is failing may not be able to generate it's normal voltage range of 0.0 to 1.0 Volts (Typically 0.450 Volts = 14.65/1) where 0.0 Volts is Lean (lots of Oxygen in the exhaust) and 1.0 Volts is Rich (very little Oxygen in the exhaust).
I think you said that you swapped the front and rear Oxygen Sensors and the problem stayed with the cylinder. This should tell you that the problem is definitely NOT the Oxygen Sensor.
