Follow the procedure below:

1. Check with the customer that the vehicle has not run out of fuel. Otherwise, the fault codes may have been stored in that condition.
2. Measure the pressure with the self-diagnosis tool by selecting the fuel pressure parameter on the low-pressure side. Be careful when selecting the "actual value" parameter. Sometimes it can also be called: "Set Value" or "Actual Value".
3. Then measure the pressure with a pressure gauge by placing it before the high-pressure pump by means of an adapter. Attempt starting and record the measured pressure. The value will depend on the speed reached during start-up. Under normal conditions, the pressure should at least reach that produced by the tank pump (3-5 bar = 300-500 kPa).
4. Compare the two (absolute) values. If an absolute pressure gauge is used, take into account that it measures 1 bar more than the value read in the self-test. An absolute manometer is easy to recognise because when placed in free air it already measures atmospheric pressure (1 bar above sea level).
5. If the readings are similar (within 1 bar tolerance). The sensor measures the correct value and should not be replaced. It will be necessary to check in order:
   1. Low pressure pump
   2. Fuel filter
   3. Discharge pipe
   4. Presence of leaks
   5. High pressure pump and flow regulator
6. If the measured value is very different from the value read in the self-diagnosis check the pressure sensor wiring and then replace it. The sensor has three connection wires. With a multimeter referring to the ground it is necessary to detect: Power supply (+5V or +12V depending on the vehicle), A ground (AC 0-0.3 Volts), A signal (0.5 Volts at 0 bar). If the sensor is faulty or disconnected, a power supply of approx. 5 Volts is present instead of the signal.

good work see you soon  

Andrea