Fuel Rail Pressure Sensor

The Fuel Rail Pressure Sensor allows monitoring of the fuel pressure in the fuel rail or injector flute. Thanks to this sensor and other components, precise fuel consumption is achieved, thus avoiding further propagation of gases into the environment.

What is the FRP Sensor?

sensor frp

It is a passive characteristic sensor. Internally it consists of a diaphragm that contains the fuel pressure and generates the resistance variation to send the signal. They are sensors with three lines or cables, power supply, output, and grounding.

This component is part of a whole automotive system designed to achieve the rational use of fuel, which is known as Diesel Common Rail.

How does the FRP Sensor work?

Thanks to the sensor signal, the computer can test what pressure the fuel hits the injector rail. In the case of vehicles with quite high-tech electronics, the circuit will comprise more components or functions of other parts.

For instance, the ECU uses the FRP sensor signals to measure the rail pressure and in turn forwards speed adjustment signals to the fuel pump. So that the rail pressure is steady. Thus achieving a consistent volume and fewer vapors are produced.

At the end of the rail, there is a diaphragm that, when actuated, turns the pressure signal into a voltage signal. The diaphragm has an electric resistivity in each layer and the pressure that is applied triggers the voltage change in each of them.

TThe withstand voltage has to be operating between 0-70 millivolts. It is then traduced or transformed by a module between 0.5 and 4.5 volts. With a tight tolerance margin, the pressure remains stable on the rail.

The function of the fuel rail pressure sensor

The basic function of the FRP sensor is to sense the constant pressure of the fuel as it reaches the injector rail. The vehicle's ECU will use the reading or signal from the sensor to control or correct the opening of the injectors so that the fuel/air mixture is the most appropriate

FRP Sensor sensor faults

The faults associated with this sensor are basic, among them are:

  • Low or high fuel pressure.
  • Low engine speed. Engine no performance.
  • The engine does not start or start intermittently.

How to Troubleshoot Fuel Rail Pressure Sensor Faults

You can do an inspection yourself and try to determine where the fault originates. This inspection starts by looking at the condition of the sensor wiring and its connectors.

Make sure that the wiring does not rub against the metal structure of the motor, as the sensor may be grounded.

Evaluate that the associated components are working optimally. Some mechanics and specialists manage to install a small pressure gauge on the rail to measure the incoming pressure, and from there evaluate it.

If the evaluation shows no damage to the wiring, no clogged filter, and the grounding is OK, you can replace the sensor.

How to test the FRP sensor?

To test the fuel rail pressure sensor, a voltmeter should be used. The positive terminal is connected to the signal output line and the negative terminal is connected to the ground. It is possible to determine the rail pressure by studying the voltage value read on the voltmeter. The signal is usually found when the motor is stopped at approximately 0.5 V.

When the starter is engaged, the voltage should rise to one or more volts. By observing the presence of this voltage value, one can be sure that the pressure is sufficient in the rail. This pressure is necessary for the injectors to open and the computer to activate them.

There are many interrelated codes for this sensor that generally point to the exact causes. When scanning your vehicle for a fault, to where this sensor is presumed to be related, the ODBII protocol will return the following codes with their meaning:

  • P0190-P0191: Low voltage. The cause can range from low fuel level, poor pump, faulty wiring, or a damaged sensor.
  • P0192: Short circuit.
  • P0193: Inadequate fuel rail pressure. Causes can be a clogged fuel filter, poor pump, and low fuel level. Damaged wiring.
  • P0194: Erratic or no corresponding signal. Usually occurs due to wiring damage. Vacuum leaks in the system.

How to clean the FRP sensor?

The sensor can become fouled by particulate fuel. Which in turn will be an indication of a collapsed filter. Therefore, it may not be the sensor that requires cleaning or replacement, but the fuel filter. Another associated component that does warrant cleaning is the vacuum hose, and make sure it is not broken.

If you make the proper revisions to your vehicle you will achieve that this FRP Sensor and others generate the expected performance in your vehicle. In addition, you will comply with the regulations related to the emission of polluting gases.

FRP Sensor Location

It is straightforward to visualize its location if you look at the injector rail. There may be a slight variation in its location for some vehicles of particular manufacturers of some models. But, in general, it will be there on the rail. You can find out the exact location of the FRP Sensor by getting the car's electrical diagrams.

This sensor has no variations that would allow it to be divided or classified by type. Regardless of its manufacturer or brand, the principle of operation remains the same.


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