Navigating car troubles can be frustrating, especially when the cryptic “Service AWD” light pops up on your dashboard. For owners of vehicles like the Chevrolet Astro, this often points to the Transfer Case Control Module (TCCM). While standard DIY OBDII scanners are excellent for diagnosing engine and transmission issues, they often fall short when it comes to accessing chassis modules like the TCCM. Facing this limitation, many car enthusiasts and DIY mechanics turn to more advanced, and often costly, diagnostic tools. But what if there was a way to delve deeper into your vehicle’s systems without breaking the bank? This is where Obdii Hacks come into play, offering a pathway to communicate directly with modules like the TCCM and uncover hidden diagnostic information.
This guide is based on a successful OBDII hack performed on a 2000 Chevrolet Astro LT AWD. While the principles discussed here are likely applicable to various General Motors vehicles of similar vintage, remember that venturing beyond standard procedures carries inherent risks. If you decide to apply these techniques to a vehicle other than a 2000 Astro, you do so at your own discretion and risk.
The beauty of OBDII hacks lies in their ability to potentially access a wider range of vehicle modules, including the Anti-lock Braking System (ABS), Transmission Control Module (TCM), and other body/chassis systems. While pinpointing the exact addresses for each module may require some investigation, the fundamental approach remains consistent.
To embark on this journey of OBDII hacking, you’ll need a few key tools. Firstly, a scanner or OBD adapter capable of console communication is essential. For this example, a ScanTool.net OBDLink SX USB adapter paired with their complimentary OBDWiz software was utilized. This combination provides a robust yet accessible platform for sending and receiving OBDII commands directly.
The knowledge to execute this OBDII hack is built upon publicly available resources. The following links offer valuable insights into OBDII communication protocols and command structures, forming the foundation for understanding and implementing these advanced diagnostic techniques:
- http://www.palmerperformance.com/forum/ … pic=4501.0
- https://theksmith.com/software/hack-veh … sy-part-1/
- https://learn.sparkfun.com/tutorials/ob … d-commands
- http://gmtnation.com/forums/topic/4947- … interface/
- https://cdn.sparkfun.com/assets/c/8/e/3 … 8b4574.pdf
Let’s delve into the practical steps of this OBDII hack. Begin by establishing a connection between your OBD adapter, computer, and vehicle. Launch your chosen OBD software and establish communication with the car, opening the console interface. This initial setup is typically straightforward. The real OBDII hack begins with understanding and sending specific commands.
The following commands were used to communicate with the TCCM on the 2000 Astro:
- ATH1 – This command activates headers, ensuring proper communication formatting.
- ATSH 6C 1A F1 – This crucial command sets the headers to target the TCCM. Let’s break it down:
- ATSH sets the header.
- 6C designates a Node to Node message type.
- 1A is the address of the TCCM.
- F1 is the address of the scan tool.
Upon successful execution, the software should return “OK,” indicating a successful header configuration.
- 19 C2 FF 00 – This command requests trouble codes from the TCCM. Here’s a detailed look:
- 19 signifies a request for Diagnostic Trouble Codes (DTCs). (Using 14 would be for clearing codes).
- C2 requests current codes. (D2 would request current and pending codes, FF for all possible codes).
- FF specifies to send all groups of codes.
- 00 is padding, used for data alignment.
The vehicle’s computer will respond with an 8-byte data packet containing the diagnostic information. Let’s decipher the format: AA BB CC DD EE FF GG HH
- AA – Byte 1: Node to Node Message confirmation (typically 6C), echoing your sent message type.
- BB – Byte 2: Recipient address (scan tool – F1).
- CC – Byte 3: Sender address (TCCM – 1A).
- DD – Byte 4: Your initial request type (19) with 40 added to it, resulting in 59 (19 + 40 = 59).
- EE – Byte 5: The first part of the DTC code.
- FF – Byte 6: The second part of the DTC code.
- GG – Byte 7: Status byte. 01 indicates “Good,” while 93 signals “MIL illuminated.” (Other status codes may exist).
- HH – Byte 8: Checksum byte (typically ignored for basic diagnostics).
To interpret the DTC code, focus on Byte 5 (EE). The first digit of Byte 5 reveals the code type:
- 0-3: P0-P3 codes (Powertrain)
- 4-7: C0-C3 codes (Chassis)
- 8-B: B0-B3 codes (Body)
- C-F: U0-U3 codes (Network/Communication)
The remaining digits of Byte 5 and Byte 6 constitute the specific code number.
In the Astro example, the TCCM returned: 6C F1 1A 59 43 10 93 E3. This translates to code C0310. The sequence 6C F1 1A 59 00 00 93 BB indicates the end of the code list and is not a DTC itself.
To clear codes, the process is similar. Instead of command 19, use 14 for the request type. First, you must request and read the codes using 19 before attempting to clear them with 14.
The command to clear codes would be:
ATSH 6C 1A F1 14
Upon successful execution, the computer should respond with 6C F1 1A 54 (Byte 4 reflecting your request type 14 + 40 = 54).
*** Remember: Always read codes first before attempting to clear them. ***
This process should clear the stored DTCs and extinguish the Malfunction Indicator Lamp (MIL), provided the underlying issue has been resolved. If the problem persists, the light will likely reappear.
Beyond the TCCM, OBDII hacks can potentially extend to other modules. Some commonly cited addresses include:
- 28 – ABS (Anti-lock Braking System)
- 40 – BCM (Body Control Module)
- 58 – SRS (Supplemental Restraint System – Airbags)
- 1A – TCCM (Transfer Case Control Module)
While the TCCM (1A) and BCM (40) have been successfully accessed in this example, communication with other addresses may vary depending on the vehicle and module implementation. Experimentation may be required, and connection attempts to unsupported modules might result in dropped connections.
OBDII hacks offer a powerful avenue for DIY mechanics and car enthusiasts to gain deeper insights into their vehicle’s health. By understanding OBDII commands and module addressing, you can potentially unlock diagnostic capabilities beyond the limitations of standard scanners. However, proceed with caution, always double-check commands and addresses for your specific vehicle, and remember that modifying vehicle systems carries inherent risks. This information is for educational purposes and should be applied responsibly.
