For automotive enthusiasts and professionals leveraging MoTeC systems, understanding the nuances of vehicle data acquisition is crucial. Often, the terms OBD CAN and vehicle CAN are used interchangeably, yet they represent distinct pathways to access your car’s information, each with its own set of characteristics. While both can provide valuable data, grasping their differences is key to maximizing your MoTeC setup’s potential.
OBD-II, a standardized system mandated for vehicles since 2007, operates on a request-response basis. If you need specific data like engine speed, your MoTeC device, acting as a diagnostic tool, sends a request message via the OBD-II port to the Engine Control Unit (ECU). The ECU then processes this request and transmits the requested information back through the OBD-II protocol. This standardized approach ensures that regardless of the car manufacturer, certain diagnostic data points are readily accessible using the same methods.
However, the vehicle’s internal CAN bus network operates differently. Here, a wealth of information, including engine RPM, wheel speeds, and various sensor readings, is often broadcast continuously across the network. This constant stream of data eliminates the need for request messages, offering a significant advantage in data acquisition speed, especially for parameters critical in performance tuning and data logging with MoTeC systems. Vehicle CAN data rates are typically much higher than OBD-II, making it ideal for capturing rapid changes in engine and vehicle dynamics. The downside is that unlike the standardized OBD-II, vehicle CAN bus communication protocols are proprietary and vary significantly between manufacturers. This necessitates reverse engineering efforts to decode and access the specific data signals relevant to your MoTeC configuration. Car companies do not publicly release these CAN bus specifications, adding a layer of complexity to direct CAN data access.
Consider a scenario where you’re configuring your MoTeC system to monitor engine RPM and wheel speed. If these channels are readily available on the vehicle CAN bus, you can set up direct CAN receive templates within your MoTeC software to capture this high-speed data stream. However, if you require information like ignition advance, which might not be broadcast on the CAN bus but is accessible via OBD-II, you would retain the OBD-II transmit message within your MoTeC communication setup. This allows you to supplement the faster CAN data with OBD-II sourced parameters, ensuring comprehensive data logging.
Conversely, if all the necessary parameters for your MoTeC application are available directly from the vehicle CAN bus, and you don’t require any OBD-II specific data, then removing the OBD-II transmit message from your configuration simplifies the data acquisition process and focuses solely on the higher-performance CAN data stream. Ultimately, the optimal approach depends on the specific data requirements of your MoTeC system and the data availability on your vehicle’s CAN bus and OBD-II systems.
