Here is the definition. You may need to have someone check the accelerator pedal position sensor and the circuit.
P2138 NISSAN Description
The Accelerator Pedal Position (APP) sensor is installed on the upper
end of the accelerator pedal assembly. The sensor detects the
accelerator position and sends a signal to the Engine Control Module
(ECM).
Accelerator pedal position sensor has two sensors. These
sensors are a kind of potentiometers which transform the accelerator
pedal position into output voltage, and emit the voltage signal to the
ECM.
In addition, these sensors detect the opening and closing speed
of the accelerator pedal and feed the voltage signals to the ECM. The
ECM judges the current opening angle of the accelerator pedal from these
signals and controls the throttle control motor based on these signals.
Idle
position of the accelerator pedal is determined by the ECM receiving
the signal from the accelerator pedal position sensor. The ECM uses this
signal for the engine operation
such as fuel cut.
Read more:
http://engine-codes.com/p2138_nissan.html#ixzz26J3D2x8s
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