GMLAN (General Motors Local Area Network) is a high-speed communication protocol used in many General Motors vehicles. Accessing real-time data from this network, specifically through OBD2, can be valuable for performance tuning, diagnostics, and custom applications. This article explores the challenges and potential solutions for tapping into the high-speed data stream of Gmlan Obd2.
One common approach to accessing vehicle data is through the body control module (BCM). The BCM often acts as a gateway between the engine control module (ECM) and the instrument panel cluster (IPC), translating high-speed GMLAN data into a low-speed protocol for the gauges. However, this translation can introduce latency, making it unsuitable for applications requiring real-time data.
Testing on a 2008 Duramax revealed that the BCM actively requests data from the ECM multiple times per second. This suggests that the ECM doesn’t continuously broadcast all gauge information. Disconnecting the BCM allowed for direct access to the ECM/TCM data stream. While standard OBD2 PIDs could still be requested using tools like Torque and EFI Live, the inherent lag of OBD2 requests remained.
The challenge lies in decoding the raw GMLAN packets to extract specific data points like boost and engine speed (RPM) at a frequency of 10Hz or higher. Reverse engineering these packets is crucial for achieving minimal latency. Has the GMLAN high-speed data packet structure been successfully reverse engineered?
While OBD2 PIDs offer a readily available solution, they might not provide the required speed for certain applications. Exploring direct access to the GMLAN data stream could offer a smoother, lower latency alternative. The ultimate goal is to process this data and convert it into an industry-standard output for seamless integration with various systems. Ideally a method for accessing GMLAN data at 10Hz or faster can be developed.
