I finally got fed up with the CEL and VSC lights coming on and decided that I would at least make a work-around.
Why it happens:
My understanding is that I get the PO138 error code every 50 miles or so is because the 4RUNNER is doing a BIT (Built In Test). The test runs the car rich for a moment and sees if the catalytic converter is doing it's job. It does this by checking the back O2 sensors which are nothing more than narrow-band sensors with 'on/off' states.
What I tried in the past:
I tried swapping the front two 'wide-band' O2 sensors as well as the back and also tried replacing the back sensors. A waste of time and money. Resetting the error code only works till the car does the BIT again.
My Solution:
Since Toyota was no help and mechanics only wanted money, I thought about what is going on and decided to just 'read' the working narrowband O2 sensor on the 'non-faulty-side' by running the sense wires from the 'bad' side. To be perfectly clear, I ran a sense wire from one 'rear' O2 sensor and piggybacked it onto the other rear sensor.
Sure enough, after I reset the computer, no more error codes! The reason? More than likely a bad ground or crappy harness issue on the one side of the exhaust. The car only wants to see a 'clean' output from the narrowband sensor. So it might only want a high or low signal and that is all.
Please note that even though one of the rear sensors is not generating a signal, it must still have the heater wires to it or this will generate an error code...AND TURN OFF THE VSC AND CREATE A CEL!!!! Unbelievable.
I am very happy to defeat this stupid scheme that Toyota has mis-engineered. It is actually quite dangerous since something as trivial as a bad ground turns off a major safety system. I told Toyota about this and they said that they appreciated my input. I asked for a case number and they said I would have to contact their lawyers!
Why it happens:
My understanding is that I get the PO138 error code every 50 miles or so is because the 4RUNNER is doing a BIT (Built In Test). The test runs the car rich for a moment and sees if the catalytic converter is doing it's job. It does this by checking the back O2 sensors which are nothing more than narrow-band sensors with 'on/off' states.
What I tried in the past:
I tried swapping the front two 'wide-band' O2 sensors as well as the back and also tried replacing the back sensors. A waste of time and money. Resetting the error code only works till the car does the BIT again.
My Solution:
Since Toyota was no help and mechanics only wanted money, I thought about what is going on and decided to just 'read' the working narrowband O2 sensor on the 'non-faulty-side' by running the sense wires from the 'bad' side. To be perfectly clear, I ran a sense wire from one 'rear' O2 sensor and piggybacked it onto the other rear sensor.
Sure enough, after I reset the computer, no more error codes! The reason? More than likely a bad ground or crappy harness issue on the one side of the exhaust. The car only wants to see a 'clean' output from the narrowband sensor. So it might only want a high or low signal and that is all.
Please note that even though one of the rear sensors is not generating a signal, it must still have the heater wires to it or this will generate an error code...AND TURN OFF THE VSC AND CREATE A CEL!!!! Unbelievable.
I am very happy to defeat this stupid scheme that Toyota has mis-engineered. It is actually quite dangerous since something as trivial as a bad ground turns off a major safety system. I told Toyota about this and they said that they appreciated my input. I asked for a case number and they said I would have to contact their lawyers!
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