The invention relates to an input module (32) for a programmable logic controller able to be connected to a plurality of elements of an automated chain, the module (32) comprising: inputs (32A, 32B), each input (32A, 32B) being able to receive the signal from at least one element of the plurality of elements, interfaces (40A, 40B), each interface (40A, 40B) being associated with a single input and comprising at least one output (40A6, 40B6) able to operate in three different states, a test block (42), and a processing sub-module (24) able to compare the state of the output (40A6, 40B6) of each interface (40A, 40B) with the state imposed by the test block (42) and to deduce an operating anomaly of the module (32, 34) therefrom.