code P2138-check engine ON after I replaced car's battery, would not accelerate , fail-safe mode

Question

Hello . I am having a very similar issue than one post i read here. This is happening intermittently.
I have a nissan sentra 2007 .
The problem started happening the next day after I replaced my car's battery ( I did it myself, since it was an emergency, so I did not use any plug-in battery saver to keep the ECM settings of my car).

The next day after I replaced the car's battery, I felt my car was not accelerating properly. Then after few trips ( maybe after 4 or 5 trips), one day my car stopped accelerating even though I pressed on the pedal (car was always on though), it threw DTC code P2138 , check engine light came on also, and would not accelerate ( i think it went into fail-safe mode).

I have my own error code reader, which that day I used it to reset the code and delete the check engine light, which allowed me to drive my car home ( it appeared that the problem was fixed, because for a while my car behaved perfectly). But the error came back after few drives once again.

Then I took it to a Nissan dealer and they told me the P2138 code was for a broken accelerator pedal position sensor, and they replaced it. I drove my car back home, and once again after few trips ( maybe 5 trips ) I again got the same error code P2138 , check engine light on again, same behavior ( would not accelerate, car is going into "fail-safe" mode)
I really do not believe the sensor was wrong at all. The dealer now is trying to make me replace the whole harness hiring and also the ECM now.
If those pieces were really broken, that day when I reset the error code in the ECM with my reader, my car would have not driven, but it drove perfectly for a while! .

What could the real problem be?. I read on some sites that when we change the car battery ourselves we could accidentally delete many of the ECM settings and that the ECM needs to re-learn many things like the "pedal re-learn procedure", "throtle valve re-learn", "iddle air voulme re-learn".
I will really appreciate some advice on what to do next.
Thanks.

Answer 1

P2138 APP Sensor circuit range / performance

Changing the battery  may have not contributed to the code condition that you have. What you have is incorrect voltage to the APP sensor, You can perform a throttle relearn and a Pedal relearn. nothing will change. You have a short. Either with the APP that has been replaced or at a sensor that supplies the reference voltage to the APP sensor.  For now the APP should be under warranty change it.