Hyundai Ioniq (AE): Rail Pressure Sensor (RPS) / Description and operation
Rail Pressure Sensor (RPS) is installed on the delivery pipe and measures the instantaneous fuel pressure in the delivery pipe. The sensing element (Semiconductor element) built in the sensor converts the pressure to voltage signal. By using this signal, the ECM can control correct injection amount and timing and adjusts the fuel pressure with the fuel pressure regulator valve if the target pressure and the actual pressure calculated by the RPS output signal are different.

Other information:
C
Removal1.Disconnect the negative (-) battery terminal.2.Remove the rear bumper.(Refer to Body - "Rear Bumper")3.Remove the rear corner radar unit (A) after loosening the mounting nuts.
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Take care not to separate the bracket from rear bumper when removing the rear corner radar sensor.