What Gauge Wire for OBD2 Extension: A DIY Guide

Creating an OBD2 extension harness can be a useful project for car enthusiasts and DIY mechanics. Whether you need to relocate your OBD2 port for better access or create a custom setup, understanding the correct wire gauge is crucial. This guide will walk you through the process of making your own OBD2 extension, focusing on selecting the right wire gauge and ensuring a reliable connection.

Understanding OBD2 Wiring and Wire Gauge

The OBD2 (On-Board Diagnostics II) port is a standardized interface in modern vehicles that allows access to the car’s diagnostic system. It uses a specific set of pins for communication, power, and ground. For a simple extension, we’ll focus on the essential wires required for basic OBD2 functionality.

Key Wires for a Basic OBD2 Extension:

• Pin 4: Chassis Ground
• Pin 6: CAN High (J-2234)
• Pin 14: CAN Low (J-2234)
• Pin 16: Battery Power

These four pins are sufficient for many OBD2 applications, including reading diagnostic trouble codes and using basic scan tools.

Why Wire Gauge Matters:

Wire gauge refers to the thickness of the wire. Choosing the correct gauge is important for several reasons:

• Current Carrying Capacity: Thicker wires (lower gauge numbers) can carry more current without overheating. While OBD2 systems don’t typically draw a lot of current, using too thin a wire can lead to voltage drop and signal degradation.
• Signal Integrity: Especially for CAN bus communication (pins 6 and 14), maintaining signal integrity is vital. Using an appropriate gauge helps ensure reliable data transmission.
• Physical Durability: A slightly thicker wire is generally more robust and less prone to damage during handling and installation.

Selecting the Right Wire Gauge for Your OBD2 Extension

For OBD2 extensions, especially for the four essential wires mentioned, 22-16 AWG (American Wire Gauge) is generally recommended and sufficient. The original guide we are referencing uses components designed for this range, specifically mentioning pins for “wire size = 22-16AWG”.

Why this range?

• Adequate Current Capacity: These gauges can easily handle the low current demands of OBD2 communication and power.
• Signal Integrity: 22-16 AWG is suitable for maintaining signal quality in OBD2 systems.
• Connector Compatibility: Many OBD2 connectors and terminals are designed to work optimally with wires in this gauge range.
• Practicality: Wires in this range are easy to work with, strip, and crimp, making them suitable for DIY projects.

While the original guide used 26AWG wires from an OBD2 cable and adapted them, it’s better practice to use the recommended gauge throughout the extension for optimal reliability and to avoid potential issues with undersized wiring.

DIY OBD2 Extension Cable: Step-by-Step Guide

This guide expands on the original article, providing a more detailed and structured approach to building your OBD2 extension.

Tools You’ll Need:

• Wire strippers/cutters
• Needle-nose pliers
• Crimping tool (Molex crimping tool recommended for professional results, but pliers can be used with care)
• Soldering iron and solder (optional, but recommended for enhanced connection reliability)
• Multimeter (optional, for testing continuity)

Parts Required:

• 4-Pin Connector: Choose a connector with pins designed for 22-16 AWG wire. (Example Link)
• OBD-II Cable or Connector: You can either use an OBD-II extension cable and cut off one end, or purchase a female OBD-II connector. (Example Cable Link or Example Connector Link)
• 22-16 AWG Wire: Choose automotive-grade wire in the colors corresponding to the OBD2 pins you’ll be using (or use different colors and label them clearly). Recommended colors based on the original article are:
  • Orange: Chassis Ground (Pin 4)
  • Green: CAN High (Pin 6)
  • Brown w/ White Stripe: CAN Low (Pin 14)
  • Green w/ White Stripe: Battery Power (Pin 16)
• Heat shrink tubing (optional, for insulation and strain relief)
• Zip ties (for cable management)

Step-by-Step Instructions:

1. Prepare the OBD2 Cable/Connector:

   • If using an OBD2 cable, carefully cut off one of the connectors, leaving a generous length of cable for your extension.
   • Carefully strip back the outer sheath of the OBD2 cable to expose the individual wires inside.
   • Identify the four wires you’ll be using based on their colors (or by tracing them back from pins 4, 6, 14, and 16 on the OBD2 connector if you are using a raw connector).

2. Prepare the Wires:

   • Cut four lengths of your 22-16 AWG wire, long enough for your desired extension length. Make them slightly longer than needed initially; you can trim them later.
   • Strip about 3/8″ (10mm) of insulation from both ends of each of the four new wires and from the ends of the four wires from the OBD2 cable.
   • Optionally, for a more secure connection, you can “tin” the exposed wire ends with solder. This involves applying a thin coat of solder to the stripped wire strands, making them more solid and easier to insert into connectors.

3. Attach Pins to Wires:

   • Slide a rubber seal (if provided with your 4-pin connector kit) onto one end of each of the four new wires.
   • Insert a wire into a pin connector from your 4-pin connector kit. Ensure the wire is positioned correctly to be crimped by the prongs of the pin.

4. Crimp or Solder the Pins:

   • Crimping (Recommended): If you have a crimping tool, use it to crimp the pin connector securely onto the wire. Ensure you crimp both sets of prongs – one onto the wire strands and the other onto the insulation/seal.
   • Soldering (Alternative or Additional): If you don’t have a crimping tool, or for extra security, you can solder the wire to the pin. Apply solder to create a strong electrical and mechanical connection. Be careful not to use excessive solder, which can make it difficult to insert the pin into the connector housing.

5. Crimp Seal Prongs:

   • Slide the rubber seal up to the back of the pin connector.
   • Use your crimping tool or needle-nose pliers to carefully fold the rear prongs of the pin connector over the rubber seal, securing it in place and providing strain relief.

6. Repeat for All Wires:

   • Repeat steps 3-5 for the remaining three wires and pin connectors.

7. Pair and Twist Wires (Optional but Recommended):

   • Pair the wires as suggested in the original guide:
     • Pin 4 (Orange) / Pin 16 (Green w/ White Stripe)
     • Pin 6 (Green) / Pin 14 (Brown w/ White Stripe)
   • Twist each pair of wires together. This can help with signal integrity, especially for the CAN bus wires (pins 6 and 14), and provides a more organized cable.

8. Insert Pins into 4-Pin Connector Housing:

   • Refer to the pinout diagram and insert the pin connectors into the correct slots in the 4-pin connector housing. The original guide specifies the following orientation:
     • Pin 14 (Brown w/ White Stripe) > Connector Slot A
     • Pin 6 (Green) > Connector Slot B
     • Pin 16 (Green w/ White Stripe) > Connector Slot C
     • Pin 4 (Orange) > Connector Slot D
   • Push each pin connector in until you hear a click, indicating it is locked in place.

9. Connect the Extension to the OBD2 Cable:

   • Now, connect the other ends of your newly wired 4-pin connectors to the corresponding wires from your OBD2 cable. Ensure you are matching the correct wires (Pin 4 to Pin 4, Pin 6 to Pin 6, etc.).
   • You can use various methods to connect these wires:
     • Soldering and Heat Shrink: The most robust and recommended method. Solder each wire pair together and insulate the connection with heat shrink tubing.
     • Crimp Connectors: Use butt splice crimp connectors to join the wires. Ensure you use connectors suitable for 22-16 AWG wire.
     • Terminal Blocks: Small terminal blocks can provide a screw-terminal connection.

10. Cable Management and Testing:

    • Use zip ties to neatly bundle the wires of your extension cable.
    • Test your OBD2 extension cable by plugging it into your vehicle and a scan tool to ensure it functions correctly. Check for continuity with a multimeter if you encounter any issues.

Conclusion

Choosing the correct wire gauge is a fundamental step in building a reliable OBD2 extension cable. Using 22-16 AWG wire provides a good balance of current capacity, signal integrity, and ease of use for DIY projects. By following these steps and paying attention to detail, you can create a custom OBD2 extension that meets your specific needs. Remember to always double-check your connections and test your extension thoroughly before relying on it for critical diagnostic work.