Are you looking to connect your OBD2 diagnostic tools to a system that utilizes a 4-pin connector? Whether you’re working on a specific vehicle, motorcycle, or an industrial application, a custom 4-pin OBD2 connector harness can be the solution. This guide will walk you through the process of creating your own, allowing you to access diagnostic information efficiently.
Before we begin, it’s crucial to understand that this is a DIY project and involves electrical work. While this guide is based on personal experience and should be helpful, always proceed with caution and at your own risk. Incorrect wiring can potentially damage your vehicle’s electronic control unit (ECU) or other systems. If you’re not comfortable with automotive wiring, it’s always recommended to consult a professional.
Tools and Parts You’ll Need
To build your 4-pin OBD2 connector harness, gather the following tools and parts:
- Wire strippers/cutters: For preparing the wires.
- Needle-nose pliers: Useful for handling small components and crimping.
- Molex crimping tool (optional but recommended): For secure and professional crimping of connector pins.
- Soldering iron (recommended): To enhance the connection and secure the wires to the pins, although crimping can be sufficient.
- 4-Pin Connector: Ensure it’s compatible with your application. This guide uses a connector available from Corsa Technic (4-pin connector link; pin/wire size = 22-16AWG; insulation/seal size = 1.3-1.7mm)). Verify the pin size and insulation requirements match your wire.
- OBD-II Cable: A standard OBD-II cable provides the necessary OBD2 connector. This guide utilizes a cable from Corsa Technic (OBD-II Cable link).
- Spare Wire (optional): If you have suitable wire on hand, you can purchase just the female OBD-II connector and wire the 4 necessary connections directly. Ensure the wire gauge is compatible with your chosen 4-pin connector.
For this project, we will focus on utilizing only four essential wires from the OBD-II connector, which typically has 16 pins. These four pins are crucial for basic CAN bus communication, commonly used in automotive diagnostics.
Understanding the 4 Essential OBD2 Pins
Out of the 16 pins on a standard OBD2 connector, we will be using these four for our 4-pin setup:
- Pin 4: Chassis Ground (Ground connection for the system)
- Pin 6: CAN High (CAN bus high signal line for data communication – J-2234 standard)
- Pin 14: CAN Low (CAN bus low signal line for data communication – J-2234 standard)
- Pin 16: Battery Power (Power supply for the OBD2 device)
Step-by-Step Guide to Building Your 4-Pin OBD2 Harness
Let’s get started with the construction process. Follow these steps carefully to create your custom harness:
Step 1: Prepare the OBD-II Cable Wires
Begin by preparing the OBD-II cable. Carefully remove the outer sheath and shielding from the end of the OBD-II cable to expose the internal wires. Identify and separate the four wires you will be using based on their pin assignments mentioned earlier: Pin 4 (Chassis Ground), Pin 6 (CAN High), Pin 14 (CAN Low), and Pin 16 (Battery Power). Typically, these wires are color-coded, but it’s always best to verify based on your specific OBD-II cable and the pinout diagram. Bundle the remaining 12 wires and secure them out of the way using a zip tie to keep your workspace tidy.
Step 2: Prepare the Wire Ends for the 4-Pin Connector
The wires within the OBD-II cable are often a smaller gauge (26AWG) than ideally suited for the pins of the 4-pin connector (designed for 22-16AWG). To ensure a secure connection, we need to slightly thicken the wire ends. Carefully strip approximately 3/8″ of insulation from the end of each of the four selected wires. Fold the exposed wire strands back over the insulated portion of the wire, and then twist the folded strands together tightly. This effectively doubles the wire thickness at the end, making it a better fit for the connector pins. Slide a rubber seal (from the 4-pin connector kit) onto each of the prepared wires. These seals provide environmental protection for the finished connection.
Step 3: Attach Wires to 4-Pin Connector Pins
Now, take the pins from your 4-pin connector kit. Observe that each pin has two sets of prongs. The front prongs are designed to crimp onto the exposed wire, while the rear prongs crimp onto the wire’s insulation (over the rubber seal). Insert the prepared wire end into the front of the pin, ensuring the exposed wire aligns with the front set of prongs. It’s important to note the small size of the wire in comparison to the pin. Using needle-nose pliers to hold the wire in place can be helpful for the next step.
Step 4: Soldering (Recommended) or Crimping the Wire to the Pin
For a robust and reliable connection, soldering the wire to the pin is highly recommended. Solder provides a strong mechanical and electrical bond, which is especially beneficial given the small wire gauge. If you choose to solder, apply a small amount of solder to the prongs, ensuring it flows and encapsulates the wire strands securely.
If you prefer to crimp, and especially if you have a Molex crimping tool, carefully crimp the front set of prongs around the exposed wire. If you don’t have a specialized crimping tool, needle-nose pliers can be used cautiously. Fold one prong at a time over the wire, using the pliers at an angle to gradually bend the metal and secure the wire. Ensure a tight crimp for good electrical contact.
Step 5: Crimp the Seal (Insulation) Prongs
Slide the rubber seal up the wire until it sits between the rear set of prongs on the pin. Using the same crimping technique as in the previous step (soldering is not needed here), fold the rear prongs over the rubber seal to secure it in place. This provides strain relief and environmental sealing at the connection point.
Step 6: Wire Pairing (Recommended for Signal Integrity)
While not strictly necessary, it’s good practice to twist pairs of wires together, especially for signal-carrying lines like CAN High and CAN Low. This technique helps to reduce electromagnetic interference and improve signal integrity. Pair and twist the wires as follows:
- Pin 4 (Chassis ground) with Pin 16 (Battery power)
- Pin 6 (CAN High) with Pin 14 (CAN Low)
Step 7: Insert Pins into the 4-Pin Connector Housing
Finally, insert the completed pins into the 4-pin connector housing in the correct orientation. Refer to the connector diagram to ensure you are placing each pin in the designated slot. The pin assignments are as follows:
- Slot A: Pin 14 (CAN Low)
- Slot B: Pin 6 (CAN High)
- Slot C: Pin 16 (Battery Power)
- Slot D: Pin 4 (Chassis Ground)
Push each pin into the rear of the connector housing until you hear an audible “click,” indicating that the pin is securely locked in place. Using needle-nose pliers to gently pull on the wire from the rear can help to ensure the pin is fully seated and locked.
Testing Your 4-Pin OBD2 Connector Harness
Congratulations! Your custom 4-pin OBD2 connector harness is now complete.
Before using it for critical diagnostics, it’s advisable to test your harness. You can do this by connecting it to a compatible system and an OBD2 scanner to check for basic connectivity and data communication. As demonstrated in the original project, this harness was successfully used to read and clear diagnostic trouble codes.
This DIY guide provides a practical approach to creating a 4-pin OBD2 connector harness. By carefully following these steps and ensuring correct wiring, you can build a valuable tool for your diagnostic needs. Remember to always double-check your connections and proceed with caution when working with automotive electrical systems.
