It has been a while since we released new functionality for the JCOM1939 Monitor software for Windows, but recent customer feedback inspired several improvements that make the software even more valuable during development, troubleshooting, and diagnostics.
The latest update introduces two important features:
- Display of the CAN Bus network condition, including receive/transmit error counters
- Support for Silent (Listen-Only) Mode
Both additions are designed to help developers better understand what is happening on the network and simplify troubleshooting when communication problems occur.
Improved CAN Bus Diagnostics
The new diagnostics originated from an interesting support request.
One of our users experimented with transmitting J1939 messages from two different nodes using the same source address. While this is certainly an unusual configuration—and definitely not recommended—it is not explicitly prohibited by the SAE J1939 standard. During testing, the user observed that some data frames appeared to be dropped.
Although we were unable to reproduce the behavior in our own laboratory, the discussion led us to investigate two possible causes:
- Poor CAN Bus network conditions, such as wiring faults, bad connections, or incorrect termination.
- A possible issue within the Windows application itself.
To help identify the first scenario, the JCOM1939 Monitor now continuously displays the overall CAN Bus condition at the top of the main window.
The software reports one of the following conditions:
- CAN Bus OK (green)
- Communication Issues (orange)
- Communication Degraded (orange)
- Communication Lost (red)
This provides immediate visual feedback whenever the network begins experiencing communication problems.
Dedicated CAN Bus Status Tab
For users who require more detailed diagnostic information, the software now includes a dedicated CAN Bus tab.
This page displays:
- Receive (Rx) error counter
- Transmit (Tx) error counter
- CAN controller error status
- CAN controller operating status
- Current CAN Bus load
Together, these values provide valuable insight into the health of the network and the behavior of the CAN controller.
The interpretation of the Rx and Tx error counters is not always straightforward. These counters are part of the CAN controller’s internal error management system and their behavior depends on numerous factors defined by the CAN protocol. Understanding their exact meaning requires some familiarity with the internal operation of CAN controllers.
We plan to cover this topic in much greater detail in a the update of the JCOM1939 Monitor User Manual. In addition, several upcoming articles on this website will explain how these counters change under different network conditions and how they can be used to diagnose communication problems.
Separating Received and Transmitted Messages
The original customer feedback also motivated another improvement.
Previously, received and transmitted messages were displayed together, making it more difficult to distinguish between locally transmitted frames and messages originating from other ECUs.
To improve readability, a future version will separate the display into two independent tables:
- Received data frames
- Transmitted data frames
This makes it much easier to verify transmitted traffic, observe network responses, and diagnose communication issues without having to manually distinguish message sources.
Silent (Listen-Only) Mode
The second major addition is support for Silent Mode, also known as Listen-Only Mode.
We will not discuss the technical implementation in detail here, as we have already covered this operating mode in separate articles on this website.
In short, Silent Mode allows the JCOM1939 Monitor to connect to an existing J1939 network without participating in bus arbitration or transmitting any messages. From the perspective of the network, the monitor is effectively invisible.
This operating mode is particularly useful for:
- Recording traffic on an existing vehicle network
- Monitoring communication during system validation
- Diagnosing communication problems without influencing network behavior
- Capturing data from production systems where transmitting messages is undesirable
To enable the feature, simply select the Silent Mode checkbox in the ECU Setup section before starting the CAN interface.
It is important to remember that Silent Mode disables all message transmission. While active, the JCOM1939 Monitor can receive and record network traffic, but it cannot transmit J1939 messages, requests, address claims, or any other CAN frames.
Availability
These new features are currently being finalized and will be included in the next release of the JCOM1939 Monitor. Before publishing the update, we are completing revisions to the User Manual to document the new CAN Bus diagnostics, network condition indicators, and Silent Mode operation. We encourage you to check this website regularly for release announcements or, even better, join the J1939 Community to receive notifications about software updates, new documentation, technical articles, and future enhancements as they become available.
Continuing to Improve Through User Feedback
Many of the recent enhancements to the JCOM1939 Monitor originated directly from customer feedback and real-world development scenarios. Features such as the CAN Bus diagnostics page, network condition indicator, and improved message display are intended to make troubleshooting faster and provide developers with more confidence when working with J1939 networks.
As always, we appreciate suggestions from our users. Real-world applications often uncover situations that are difficult to reproduce in the lab, and those experiences continue to shape future releases of the JCOM1939 Monitor.
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