Building your own scan tool for older vehicles using the ALDL (Assembly Line Diagnostic Link) system, often mistakenly referred to as OBD2 due to the similar connector, is a rewarding project for any car enthusiast or DIY mechanic. This guide will walk you through the process of creating a simple yet effective ALDL scan tool, focusing on the pinout and connections required. While the term “Aldl Obd2 Pinout” might lead to confusion as ALDL is pre-OBD2, understanding the ALDL pinout is crucial for diagnosing and working on classic cars that utilize this system.
This project is cost-effective and provides a hands-on understanding of automotive diagnostics. Let’s dive into the steps.
Step 1: Gather Your Components
To start, you’ll need a few key components. The heart of our project involves connecting an OBD2 connector to a USB interface, utilizing an FTDI breakout board.
- OBD2 to USB Cable: Acquire a cheap OBD2 to USB cable. The goal here isn’t to use the cable’s electronics but rather to repurpose the OBD2 connector itself and its convenient pin layout. These cables are readily available online.
Alt text: OBD2 connector from a USB diagnostic cable, highlighting the standard 16-pin layout.
- OSEPP FTDI (FTD-01) Breakout Board (FTDI FT232RL Chip): This breakout board is essential for converting the TTL serial signals from the ALDL system to USB for your computer to read. Ensure it uses the FTDI FT232RL chip and can operate at 5V, which is necessary for this application.
Alt text: OSEPP FTDI FTD-01 breakout board with FT232RL chip, used for USB to serial conversion.
Step 2: Disassembling the OBD2 Connector
Now, we need to access the pinout of the OBD2 connector from the cable.
- Open the OBD2 Connector Housing: Carefully disassemble the OBD2 connector housing. Usually, small Philips head screws hold it together. Precision screwdrivers will be helpful for this step.
Alt text: Disassembling the plastic housing of an OBD2 cable connector to access the internal circuit board.
- Separate the Circuit Board: Once open, you’ll see a small circuit board connected to the OBD2 port header. Carefully separate the circuit board from the OBD2 port. Bending the metal tabs back and forth will weaken them until they break, or you can use wire cutters for a cleaner separation.
Alt text: Detaching the internal PCB from the OBD2 connector by bending and breaking the connecting tabs.
Step 3: Preparing the OBD2 Connector for Wiring
With the circuit board removed, we need to prepare the OBD2 connector for our direct wiring.
- Remove Metal Pin Headers: On the back of the OBD2 connector, you’ll likely see metal pin headers where the circuit board was attached. These need to be removed to prevent shorts and to give us clean solder pads. Use wire cutters to snip them off or desolder them if you prefer.
Alt text: Rear view of the OBD2 connector after PCB removal, indicating the metal pin headers to be removed.
- Cleaned OBD2 Connector: After removing the unnecessary components, you should have a clean OBD2 connector ready for wiring.
Alt text: Prepared OBD2 connector with solder pads exposed, ready for direct wiring to the FTDI board.
Step 4: Wiring the ALDL OBD2 Pinout to the FTDI Board
Now comes the crucial part: connecting the OBD2 connector to the FTDI breakout board, paying close attention to the ALDL pinout. Remember, we are working with ALDL (OBD1), and while we are using an OBD2 connector for convenience, the protocols are different.
- Prepare Wires: Cut off the USB end of the OBD2 to USB cable and strip back the outer rubber and wire shielding. Inside, you’ll find several wires. For ALDL communication, we primarily need three: Ground, and the Data Transmit/Receive line. Typically, these are Black (Ground), and Green/White (Data). In this example, the red wire is not needed and can be eliminated.
Alt text: Essential tools for the DIY ALDL scan tool project: soldering iron, solder, screwdrivers, and wire strippers.
- Connect to OBD2 Connector: Solder the wires to the OBD2 connector pins as follows, focusing on the ALDL pinout configuration:
- Ground (Black wire): Solder to Pin #5 on the OBD2 connector. Pin 5 is the designated Ground for ALDL systems in many vehicles.
- Data (Green and White wires combined): Solder these two wires together and then connect them to Pin #9 on the OBD2 connector. Pin 9 is commonly the ALDL data line for both transmit and receive in many GM ALDL implementations.
Alt text: Wiring process showing the green and white wires soldered together and connected to pin 9, and the black wire to pin 5 of the OBD2 connector.
- Connect to FTDI Breakout Board: Now connect the other ends of these wires to the FTDI breakout board:
- Green/White (Data): Solder to both the TXD and RXD pads on the FTDI board. For ALDL, the data line is bidirectional, so connecting to both TXD and RXD ensures proper communication.
- Black (Ground): Solder to the GND pad on the FTDI breakout board.
Alt text: Soldering the green/white data wires to TXD and RXD, and the black ground wire to GND on the FTDI breakout board.
- Secure Solder Connections: Ensure all solder joints are solid and make good electrical contact. Add more solder to the bottom pads of the FTDI board for a stronger connection if needed. Trim any excess wire.
Alt text: Detailed view of the clean and secure solder joints on the FTDI breakout board pads.
Step 5: Final Assembly and Testing
Your DIY ALDL scan tool is almost complete!
- Final Product: Inspect your wiring and connections one last time. Ensure there are no shorts or loose wires.
Alt text: The finished DIY ALDL scan tool, showcasing the OBD2 connector wired to the FTDI breakout board.
- MicroUSB Cable: You’ll need a microUSB cable to connect the FTDI breakout board to your computer.
Alt text: A standard MicroUSB cable, necessary for connecting the FTDI based scan tool to a computer.
With your DIY ALDL scan tool built for around $26 and an hour of your time, you’re ready to diagnose compatible ALDL vehicles. Remember to use appropriate ALDL scanning software on your computer to interpret the data. While this guide focuses on the “aldl obd2 pinout” in search terms, always refer to your vehicle’s specific service manual for the correct ALDL pinout and diagnostic procedures. This project provides a foundation for understanding OBD1 systems and offers a practical tool for working on older vehicles.
