Method for functionality control of a high pressure pump in a system for fuel injection in a combustion engine, wherein the system comprises a feeding pump controllable independently of the combustion engine, for the supply of fuel in a low pressure part of the system to the high pressure pump, which comprises at least one pump element which is connected between said low pressure part and an accumulator tank for fuel injection to the combustion engine, and which has one cylinder with a pump chamber with a moveable piston for pumping therein, and an inlet valve arranged in this cylinder's connecting opening to the lower pressure part, which is controllable in order to control the flow of fuel into the pump chamber, wherein, during stationary operating modes of the combustion engine with a constant requested reference value (P B) for the fuel pressure in the accumulator tank, the following steps are carried out: a) measurement of the fuel pressure (P in) in one position in said low pressure part at the inlet to the high pressure pump, b) control of the feeding pump, so that said fuel pressure (P in) in said position in the low pressure part falls and simultaneous measurement of this fuel pressure (P in), c) measurement of the fuel pressure in said accumulator tank (P s) during the pressure reduction in the low pressure part carried out in step b), d) comparison of the development of the fuel pressure (P s) measured in step c) with said requested reference value (P B) during the pressure reduction in the low pressure part in step b), e) generation of information about the high pressure pump's functionality, based on the comparison in step d), and wherein in step b) the reduction of the fuel pressure (Pi n) in said position in the low pressure part is carried out toward a predetermined minimum pressure (P min), as of which the high pressure pump in normal functioning is incapable of delivering a fuel pressure (P s) in the accumulator tank which reaches said requested reference value (P B), and in that the fuel pressure in said position in the low pressure part at which the fuel pressure (P S) in the accumulator tank falls below said reference value (P B), is registered as a limit pressure (P G), and the pressure reduction in step b) is carried out down to a pressure which is higher than or equal to said minimum pressure (P min), and in that the fuel pressure in the low pressure part at which the comparison in step d) provides a measurable difference, is registered as said limit pressure and used to determine the pump's functionality. a) measurement of the fuel pressure (P in) in one position in said low pressure part at the inlet to the high pressure pump, b) control of the feeding pump, so that said fuel pressure (P in) in said position in the low pressure part falls and simultaneous measurement of this fuel pressure (P in), c) measurement of the fuel pressure in said accumulator tank (P s) during the pressure reduction in the low pressure part carried out in step b), d) comparison of the development of the fuel pressure (P s) measured in step c) with said requested reference value (P B) during the pressure reduction in the low pressure part in step b), e) generation of information about the high pressure pump's functionality, based on the comparison in step d), and wherein