Hyundai Sonata LF: Engine Control System / 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.

Inspection
1.
Turn the ignition switch OFF.
2.
Disconnect the HO2S connector.
3.
Measure resistance between the HO2S terminals 2 and 5 [B1/S1]...
Other information:
C..
Description
The Knee Airbag (KAB) is installed inside the crash pad lower
panel and protects the driver in the event of a frontal crash. The
SRSCM determines if and when to deploy the KAB.
Never attempt to measure the circuit resistance of the airbag
module (squib) even if you are using a specified tester...