As a car enthusiast and DIY mechanic, delving into the intricacies of vehicle diagnostics has always been a passion. Recently, my curiosity was piqued by discussions around vehicle network vulnerabilities, specifically the FCA Uconnect hack. This led me down a rabbit hole of exploring Controller Area Network (CAN bus) communication and OBD2 Parameter IDs (PIDs). For those unfamiliar, OBD2 PIDs are codes used to request data from a vehicle’s onboard computer, offering a window into a vast array of sensor readings and system statuses. While standard OBD2 PIDs are well-documented, manufacturer-specific or extended PIDs, like those for General Motors (GM) vehicles, often remain shrouded in mystery. This exploration is about uncovering the secrets hidden within the GM OBD2 system, focusing on creating a comprehensive Gm Obd2 Pid List through practical investigation and reverse engineering.
Understanding OBD2 PIDs and the GM Specific Challenge
OBD2 (On-Board Diagnostics II) is a standardized system providing access to vehicle diagnostic information. PIDs are the backbone of this system, each acting as a request for a specific piece of data – engine temperature, speed, RPM, and much more. While generic PIDs offer a baseline for diagnostics across manufacturers, accessing advanced data often requires understanding manufacturer-specific PIDs. GM, like other automakers, utilizes extended PIDs beyond the standard set to monitor a wider range of parameters unique to their vehicles. The challenge lies in the fact that a definitive, publicly available gm obd2 pid list is not readily provided by the manufacturer. This necessitates a more hands-on approach to uncover these valuable data points.
Exploring the Realm of Extended GM PIDs
My journey started by leveraging a full PID scan using the Torque app and an OBDLink MX adapter. This process revealed a crucial insight: the extended PIDs responding with “7F” (a NULL PID response) are actually potential candidates for containing valuable, yet undocumented data. Essentially, the PIDs that were skipped or returned null responses during a standard scan became prime suspects for harboring functional, enhanced PIDs. By meticulously analyzing the full PID scan data and identifying these skipped PIDs, we can begin to narrow down the search for functional extended GM PIDs. This method allows us to move beyond the limitations of standard OBD2 protocols and delve into the proprietary data streams within GM vehicles.
Tools and Methodology for PID Discovery
To further this investigation, upgrading the diagnostic hardware is essential. Bluetooth OBD2 adapters, while convenient, can suffer from bandwidth limitations and data buffer overflows, especially when monitoring continuous OBD2 traffic. To overcome this, a wired USB OBD2 ELM327 module is the logical next step. This wired connection ensures a stable, high-bandwidth data stream, crucial for capturing complete and uninterrupted CAN bus communication. This robust connection will enable continuous monitoring without data loss, paving the way for more reliable PID discovery and data analysis.
Unlocking Potential GM Vehicle Data Points
The potential benefits of uncovering a comprehensive gm obd2 pid list are vast. Imagine accessing real-time tire pressure and temperature data directly from the TPMS (Tire Pressure Monitoring System) – information often communicated within the vehicle network but not readily available through standard OBD2. Similarly, exploring PIDs related to features like window rollup/rolldown modules opens up possibilities for understanding and potentially customizing vehicle functionalities. My initial curiosity about an aftermarket OBD2 window control module led to investigating the unlock/lock sequences on the CAN bus. By using an OBD2 splitter cable, I plan to simultaneously monitor CAN bus traffic while the window module is active. This “sniffing” approach can reveal the communication protocols and potentially identify PIDs associated with various vehicle control functions.
Moving Forward: CAN Bus Sniffing and Reverse Engineering
The next phase of this exploration involves actively trapping communication on the CAN bus using the wired ELM327 scanner. The goal is to determine if data points like TPMS pressure and temperature are indeed transmitted from modules like the BCM (Body Control Module) to the ECM (Engine Control Module). Observing CAN bus traffic while interacting with vehicle systems, such as switching the driver information center (DIC) to the TPMS screen, could reveal the specific data packets and associated PIDs used to display this information. This hands-on approach, combined with analyzing the previously identified potential extended PIDs, forms a robust strategy for reverse engineering the GM OBD2 PID landscape.
For those interested in delving deeper into vehicle network communication and OBD2 hacking, resources like the “Car Hacker’s Handbook” and guides on cheap vehicle bus hacking (links below) provide invaluable foundational knowledge.
a complete guide to hacking your vehicle bus on the cheap & easy – part 1 (hardware interface) |
a complete guide to hacking your vehicle bus on the cheap & easy – part 2 (interpreting the data) |
https://cdn.sparkfun.com/assets/learn_tutorials/8/3/ELM327DS.pdf
http://opengarages.org/handbook/2014_car_hackers_handbook_compressed.pdf
This journey into deciphering the gm obd2 pid list is an ongoing process of discovery. By combining systematic PID scanning, robust hardware, and a curiosity to explore the hidden depths of vehicle communication, we can unlock valuable insights and potentially expand the possibilities of vehicle diagnostics and customization. Stay tuned for updates as this exploration progresses!
