For BMW enthusiasts and track day aficionados, maximizing vehicle performance and understanding detailed telemetry data are key. While OBD2 (On-Board Diagnostics II) has been the standard interface for accessing basic car diagnostics, unlocking the full potential of your BMW, especially models like the 2011 F20 and newer, often requires diving into the CAN-bus (Controller Area Network) system. This guide explores the advantages of using CAN-bus for advanced data acquisition in BMWs, offering a pathway to richer, more granular insights into your car’s performance.
Understanding OBD2 and CAN-bus in BMWs
OBD2 is a standardized system primarily designed for emissions monitoring and basic diagnostics. It provides access to a limited set of parameters, which is often sufficient for generic scan tools and basic performance apps. However, for in-depth performance analysis, especially on track, OBD2 falls short.
CAN-bus, on the other hand, is a more comprehensive communication network within your BMW. It’s the backbone for various electronic control units (ECUs) to communicate with each other, exchanging a vast amount of data related to engine performance, chassis dynamics, and much more. Accessing CAN-bus data opens up a world of possibilities for detailed telemetry, far beyond what OBD2 can offer.
Why CAN-bus for Advanced Telemetry?
For BMW owners seeking serious track performance data, CAN-bus offers several key advantages over OBD2:
- Higher Data Resolution and Frequency: CAN-bus transmits data at much higher frequencies than OBD2. This means you get more data points per second, providing a smoother and more accurate representation of dynamic parameters like RPM, throttle position, and wheel speed. The original article mentions seeing ~1750 CAN frames per second compared to the slower OBD2 data rates.
- Wider Range of Parameters: CAN-bus exposes a significantly broader range of data parameters that are simply not available through OBD2. This includes detailed engine data, advanced chassis information, individual wheel speeds, steering angle, and much more, crucial for track analysis and performance tuning.
- Real-time Data Access: CAN-bus allows for near real-time data streaming, essential for live telemetry displays and immediate performance feedback during track sessions.
While OBD2 is accessible via a standardized port, tapping into CAN-bus requires a bit more technical know-how but unlocks a wealth of information. For models around the 2011 BMW F20 era and onwards, manufacturers increasingly rely on CAN-bus for core vehicle communication, making it the ideal source for comprehensive telemetry data.
Step-by-Step DIY Guide to Accessing BMW CAN-bus Data
This guide outlines a general approach to accessing CAN-bus data in BMWs for telemetry purposes. While the original article focused on a G8x model, the principles are applicable to a range of BMWs, including models around the 2011 F20. Disclaimer: Working with vehicle electronics requires caution. If you are not comfortable with automotive wiring, consult a professional.
1. Tapping into the CAN-bus Network
The first step is to physically access the CAN-bus wires in your BMW. A common location to find CAN-bus connections is in the passenger footwell area. CAN-bus wires are typically twisted pairs, which helps in identifying them.
CAN-bus Wiring Color Code (General BMW):
- CAN High: Yellow/White
- CAN Low: Yellow/Black
Important: Always verify the CAN-bus wiring colors for your specific BMW model and year using a reliable wiring diagram or service manual.
To tap into the CAN-bus wires without damaging the factory harness, consider using posi-taps or similar non-destructive connectors. JST connectors can be useful for creating easily disconnectable connections for your data logging device.
2. Decoding CAN-bus Data
Once you have physical access to the CAN-bus, the next challenge is to decode the raw CAN-bus messages. Car manufacturers typically do not publicly release CAN-bus data protocols, making this a reverse-engineering process.
Tools like a Raspberry Pi with a CAN-bus interface (e.g., PiCAN2 hat) and software like candump and cansniff are invaluable for logging and analyzing CAN-bus traffic.
By analyzing the logged data while varying vehicle parameters (e.g., accelerating, braking, steering), you can correlate CAN-bus messages with specific vehicle data points. The original article provides a Google Sheet link with decoded CAN-bus data for a G8x BMW, which can serve as a starting point, although CAN-bus protocols can vary between BMW models and years.
Common Telemetry Parameters to Look For:
- RPM
- Throttle Position
- Gear
- Speed
- Wheel Speeds (individual)
- Steering Angle
- Acceleration (Longitudinal and Lateral)
- Yaw Rate
- Temperatures (Coolant, Oil, Air Intake)
- Battery Voltage
3. Setting up an ESP32 Device for Data Acquisition
To stream CAN-bus data wirelessly to a telemetry app, an ESP32 microcontroller is a powerful and cost-effective solution. The ESP32 has built-in CAN-bus capabilities (requiring a transceiver) and Bluetooth Low Energy (BLE) for wireless communication.
Components like the Adafruit Feather ESP32 and CAN-bus FeatherWing transceiver simplify the hardware setup.
Basic soldering is required to assemble the ESP32 device. Program the ESP32 to read CAN-bus data, parse the desired parameters, and transmit them via BLE. The original article author has shared source code on GitHub (link provided in the original article) which can be a valuable resource.
4. Integrating with RaceChrono (or Similar Software)
Telemetry apps like RaceChrono offer excellent support for custom CAN-bus data inputs via Bluetooth LE. Within RaceChrono, you can configure custom channels and apply formulas to convert raw CAN-bus data into human-readable values and units.
By setting up the ESP32 device and configuring RaceChrono, you can create a powerful DIY telemetry system that leverages the rich CAN-bus data available in your BMW, providing significantly more insights than OBD2-based solutions.
Conclusion
Accessing CAN-bus data in your BMW opens up a new dimension of vehicle telemetry and performance analysis. While OBD2 provides basic diagnostics, CAN-bus unlocks a wealth of real-time, high-resolution data crucial for track day enthusiasts and those seeking a deeper understanding of their BMW’s performance. By following the steps outlined and leveraging resources like the provided example project, you can build a custom telemetry system that rivals professional setups, empowering you with unparalleled insights into your driving and your machine. Explore the possibilities of CAN-bus and take your BMW performance analysis to the next level.
