Modern vehicles are complex networks of sensors and computers constantly communicating. Accessing this data stream can be invaluable for diagnostics, performance tuning, and even building custom carputer systems. At the heart of this communication lies the OBD2 port and the language it speaks: Parameter IDs (PIDs). Understanding how an Obd2 Pid Reader works is key to unlocking the secrets hidden within your car’s data.
Understanding OBD2 and CAN Bus
All cars manufactured after 2008 utilize a dual Controller Area Network (CAN) bus system: a high-speed CAN bus (500kbps) and a low-speed CAN bus (33kbps). Standard OBD2 data, such as Diagnostic Trouble Codes (DTCs), are transmitted over the high-speed CAN bus. Meanwhile, data for accessories like air conditioning and the stereo typically travel on the low-speed CAN bus.
General Motors (GM) introduced GMLAN in 2005, a variation on this standard. In GMLAN-equipped vehicles, all lower-speed functions utilize the 33kbps bus, while engine control and critical systems communicate via the high-speed bus.
Reading OBD2 Data with an Arduino
Accessing this wealth of information requires an OBD2 PID reader, and a common DIY solution involves using an Arduino microcontroller with a CAN bus shield. This allows direct access to the CAN bus data pins, bypassing the need for complex serial port reconfiguration. For instance, in a GMLAN system, the CAN high and low lines can be accessed directly from specific pins on the OBD2 connector (e.g., pin 1 for GMLAN).
The provided code demonstrates using an Arduino UNO with a SparkFun CAN bus shield to read both high and low-speed CAN data. It utilizes the arduino-CAN library to decode the raw CAN messages into usable packets. This raw data includes:
- ID: The unique identifier for the data packet.
- RTR: Remote Transmission Request flag.
- IDE: Identifier Extension flag.
- DLC: Data Length Code.
- Data: The actual data payload.
Filtering for Relevant PID Changes
The challenge lies in filtering this constant data stream to isolate specific PIDs and only display changes. This is crucial for a dynamic display, showing real-time updates without overwhelming the user with redundant information.
One approach involves storing the previous value of each desired PID. When a new CAN message arrives, the code extracts the PID and its associated data. If the new data differs from the previously stored value, it’s sent to the serial monitor. This ensures only changes are displayed. This filtered data can then be easily processed by a Python script for a customized carputer display.
Conclusion: Harnessing the Power of OBD2 PIDs
Understanding how to read and filter OBD2 PIDs opens up a world of possibilities. From basic diagnostics to advanced data analysis for performance tuning, an OBD2 PID reader is an essential tool for any car enthusiast or professional mechanic. With readily available hardware like Arduino and open-source libraries, building a custom solution to unlock your car’s hidden data is within reach.
