The present invention is directed towards an ambulatory infusion device, comprising:a) a sensor assembly (102, 112) with a sensor (102), the sensor assembly (102, 112) being configured to provide an output variable in dependence of an infusion variable and in dependence of a supply variable,b) a supply unit (104), the supply unit (104) being coupled to the sensor (102) and being configured to provide the supply variable,characterized byc) a sensor testing unit (114) for verifying correct operation of the sensor assembly (102, 112), the sensor testing unit (114) being coupled to the sensor assembly (102, 112) and the supply unit (104), the sensor testing unit (114) being configured to carry out a sensor testing sequence, the sensor testing sequence comprising the steps of controlling the supply unit (104) to vary the supply variable and to determine whether the variation of the supply variable is reflected by an expected variation of the output variable.The invention is further directed towards a method verifying correct operation of a sensor assembly (102, 112) of an ambulatory infusion device by carrying out a sensor testing sequence, the sensor testing sequence comprising varying a supply variable which is provided to a sensor (102) of the sensor assembly (102, 112) and determining if the variation is reflected by an expected variation of the output signal of the sensor assembly (102, 112).
