OBD2 (On-Board Diagnostics) is a valuable tool for accessing vehicle data, but its relationship with the CAN bus (Controller Area Network) often causes confusion. This article clarifies how OBD2 and CAN bus interact, answering the crucial question: Is Can Bus Monitored By Obd2?
Understanding OBD2 and CAN Bus
OBD2 is a standardized system that allows external devices to access diagnostic and real-time data from a vehicle’s electronic control units (ECUs). CAN bus, on the other hand, is a communication protocol used by ECUs to exchange information within the vehicle. Think of CAN bus as the language and OBD2 as a translator.
Since 2008, all cars sold in the US are required to use CAN bus as the underlying communication protocol for OBD2, as per the ISO 15765 standard. However, this doesn’t mean OBD2 monitors all CAN bus traffic.
How OBD2 Accesses CAN Bus Data
OBD2 doesn’t passively monitor the entire CAN bus. Instead, it actively requests specific data from ECUs. Here’s how it works:
- Request: An OBD2 scanner sends a request message over the CAN bus, targeting a specific ECU or all ECUs (using a broadcast address). This request includes a parameter ID (PID) specifying the desired data.
- Response: If the targeted ECU supports the requested PID, it responds with the corresponding data over the CAN bus.
- Decoding: The OBD2 scanner then decodes the received data and displays it to the user.
OBD2’s Limited View of CAN Bus
Crucially, OBD2 only sees the data it specifically requests. It doesn’t have access to the continuous stream of messages exchanged between ECUs for vehicle operation. This is because:
- Proprietary Protocols: Car manufacturers use proprietary CAN bus protocols for internal communication, which are not part of the OBD2 standard.
- Security and Gateway Modules: Many modern vehicles use gateway modules to filter CAN bus traffic, preventing unauthorized access to sensitive data through the OBD2 port. This safeguards the vehicle’s systems from potential security threats.
Conclusion: Monitoring vs. Accessing
While OBD2 utilizes the CAN bus to communicate with ECUs, it doesn’t passively monitor all CAN bus activity. It only accesses specific data points based on requests. Thinking of OBD2 as a targeted data retrieval system rather than a comprehensive monitoring tool provides a more accurate understanding of its functionality. To access the full range of CAN bus data, specialized tools like CAN bus data loggers are required. These loggers connect directly to the CAN bus network, capturing all messages without relying on OBD2 requests.
Logging and Decoding OBD2 Data
For practical applications, tools like the CANedge data logger can be used to record OBD2 data. This device can be configured to send specific OBD2 requests and log the responses. The logged data can then be decoded using specialized software and DBC (Database Container) files, providing valuable insights into vehicle performance and diagnostics.
Want to learn more about CAN bus and data logging? Explore our comprehensive resources: https://www.csselectronics.com/pages/can-bus-intros-tutorials Contact us for expert advice: https://www.csselectronics.com/pages/contact-us
