Response: ""CAN_2:111,0000,K-Line:1"" - Confirms that connection was made correctly at the initial moment of the installation and ignition of vehicle was turned on, therefore data messages can be received.
""I checked our server and saw that the tachograph messages were present (198, 184, 231 etc.) but they all had a value of 0."" - Was the ignition on during this period? If ignition is off (Example"" External voltage is 24,5 V and not ~27 V it is logical to expect that data-bus is in sleep mode and no data should be transmitted). Additionally, if K-line was the only source configured for ""Tachograph Data"" and K-Line was disconnected at that moment no data would have been read.
As for initial point, we kindly suggest to double-check if K-Line wire is not disconnected at this moment, as there does not seem to be any other reasonable sources for this type of issue.