This article describes the reason for the Tx passive mode at the CAN interface or Analysis tool.
CAN PC Interfaces, CAN interface board
Receives a CAN controller a message on the CAN bus, it automatically sends an acknowledgment. Regardless whether the message was intended for this device or not. Due to this, the transmit node knows that the transmission was successful. However, this does not guarantee the error free reception of the message by the desired target node.
If a CAN PC interface is connected to the network, it will normally send an acknowledgment for each received message. For analyzing a CAN network and to find errors, the PC interface should not interfere in the communication. Since this can change the network behavior and worst case cover up the error.
If "Tx passive mode" (Listen only mode) is activated, the interface will only receive messages, without acknowledgement.