Control method for an overpressure valve in a common-rail fuel supply system

1) Control method for an overpressure valve (12) in a common-rail fuel supply system (1), the method including the step of:

• delivering fuel under pressure, via a high-pressure pump (6), to a common rail (5) equipped with the overpressure valve (12) that is set to discharge the fuel present in the common rail (5) into a discharge line (11) when the fuel pressure inside the common rail (5) exceeds a safety value (psafety);
• the method is characterized in that it includes the additional steps of:
• piloting, during a diagnostic test, the high-pressure pump (6) to increase the fuel pressure inside the common rail (5) beyond the safety value (psafety) in order to trigger operation of the overpressure valve (12);
• determining, during the diagnostic test, the flow (mHP) of the high-pressure pump (6) and/or the fuel pressure inside the common rail (5);
• comparing the flow (mHP) of the high-pressure pump (6) and/or the fuel pressure inside the common rail (5) during the diagnostic test with respective threshold values (mtest and ptest);
• and
• diagnosing malfunctioning of the overpressure valve (12) if the flow (mHP) of the high-pressure pump (6) is less than a respective flow threshold value (mtest) and/or the fuel pressure inside the common rail (5) is greater than a respective pressure threshold (ptest).