The invention relates to a work machine and a method for monitoring a control system at a work machine (1a). According to the method, in-parameters (32, 34, 36, 38) are obtained in the form of signals from the control system, wherein the control system generates actual values on one or more out-parameters (42, 44) in the form of signals based on said in-parameters. A characteristic of the invention is that a digital flow of data, comprising both said in-parameters and out-parameters via a control bus (5a, 5b), is addressed to a RAM buffer memory (3b,3c), which is included in a personal computer (3a) onboard the work machine, which buffer memory in FIFO mode writes a data file (id:1.1-id1:n) of a predetermined size, which is saved in a non-volatile data support memory (3d).