Drive control unit for an ambulatory infusion device drive, the ambulatory infusion device drive comprising a stepper motor, wherein the ambulatory infusion device drive is configured to repeatedly execute a drive control sequence, the drive control sequence comprising the steps of: a) actuating the stepper motor to execute a requested steps number in a current drive control sequence; b) receiving a drive member position, the drive member position being indicative of an actual position of a drive member following the actuation; c) computing, from the drive member position and the requested steps number, a missed steps number as deviation between the requested steps number and an executed steps number in the current drive control sequence; characterized by d) determining, based on a statistical evaluation of a time-distribution of the missed steps number over a history of drive control sequences, if the ambulatory infusion device drive is blocked; wherein the drive control unit is further configured, if it is determined that the ambulatory infusion device drive is blocked, to generate a blockage alarm signal, wherein the drive control unit stores score values for pairs of executed steps numbers and missed steps numbers, wherein the drive control unit is further configured to carry out a method which includes retrieving a score value as determined by the executed steps number and missed steps number, computing a score sum of score values for a pre-determined number of past and consecutive successive sequences, and comparing the score sum with a score sum threshold, wherein the method includes: d') determining if the missed steps number exceeds a first missed steps threshold, and d'1) if the missed steps number does not exceed the first missed steps threshold, decrease a score value by a score decrease value, d'2) or, alternatively, if the missed steps number does exceed the first missed steps threshold, increase the score value by a score increase value; wherein determining if the ambulatory infusion device drive is blocked includes determining if the score value exceeds a score value threshold. a) actuating the stepper motor to execute a requested steps number in a current drive control sequence; b) receiving a drive member position, the drive member position being indicative of an actual position of a drive member following the actuation; c) computing, from the drive member position and the requested steps number, a missed steps number as deviation between the requested steps number and an executed steps number in the current drive control sequence; d') determining if the missed steps number exceeds a first missed steps threshold, and d'1) if the missed steps number does not exceed the first missed steps threshold, decrease a score value by a score decrease value, d'2) or, alternatively, if the missed steps number does exceed the first missed steps threshold, increase the score value by a score increase value; d'1) if the missed steps number does not exceed the first missed steps threshold, decrease a score value by a score decrease value, d'2) or, alternatively, if the missed steps number does exceed the first missed steps threshold, increase the score value by a score increase value; wherein determining if the ambulatory infusion device drive is blocked includes determining if the score value exceeds a score value threshold.