If you’re using a plug-and-play device that connects to your car’s OBD2 port, like a vehicle tracker, and it’s not powering on, a blown fuse is a common culprit. The OBD2 port, while seemingly a direct power source, relies on your car’s electrical system and, crucially, a fuse to deliver that power. Understanding which fuse powers your OBD2 port is the first step in diagnosing power issues.
Before diving into fuse boxes and multimeters, let’s cover some quick initial checks to make sure the problem isn’t something simpler.
Quick Checks for OBD2 Device Power Issues
Often, the issue isn’t a blown fuse but a loose connection. Here’s how to quickly rule out connection problems:
Check OBD-II Port Connections
If your device isn’t beeping or showing signs of power when plugged into the OBD2 port, the first step is to ensure a secure connection.
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Direct Connection: If you’re plugging the device directly into the OBD2 port, unplug it and firmly plug it back in. Sometimes a slight nudge is all it takes to establish a good connection.
Alt text: Close-up view of a hand plugging an OBD-II device into a car’s OBD-II port, emphasizing the secure connection needed for power.
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Extension Cable Connections: If you’re using an OBD2 extension cable, there are a couple of connection points to check:
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Cable to OBD-II Port:
- Turn off your car’s engine.
- Disconnect the extension cable from the car’s OBD2 port.
- Wait for about 5 minutes, then firmly reconnect it. Listen for a beep from your device, indicating power.
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Device to Cable:
- With the engine off, unplug the device from the extension cable.
- Wait 5 minutes.
- Reconnect the device to the cable securely and listen for a beep.
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Test the Device Directly
To isolate whether the issue is with the device itself or the cable, try plugging the device directly into the OBD2 port, bypassing the extension cable altogether.
- Disconnect the extension cable from both the OBD2 port and the device.
- Plug the device directly into the OBD2 port.
- If the device now powers on (beeps), the problem likely lies within the extension cable or its fuse.
Checking the Device Cable Fuse
Many OBD2 extension cables come with an inline fuse to protect the device and your car’s electrical system. This fuse can blow, preventing power from reaching your device.
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Locate the Fuse Holder: Find the fuse holder on your OBD2 extension cable. It’s usually a small, black plastic compartment.
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Open the Fuse Holder: Open the cap of the fuse holder to access the fuse. You might need a small screwdriver or your fingernail to pry it open.
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Inspect the Fuse: Remove the fuse and check the thin wire inside. If the wire is broken or the inside is blackened, the fuse is blown and needs replacement.
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Replace the Fuse: Replace the blown fuse with a new fuse of the same type and amperage (usually a 3A mini-blade fuse). These are readily available at auto parts stores.
Alt text: A close-up shot of a fuse holder on an OBD-II cable being opened to check the fuse inside, highlighting the process of accessing and inspecting the fuse.
Checking the Car’s OBD2 Port Fuse
If the device cable fuse is fine, or you’re plugging directly into the OBD2 port, the next step is to investigate your car’s fuse box. The OBD2 port is powered by a fuse in your vehicle’s fuse panel, and this fuse can also blow, cutting off power to the port.
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Locate Your Car’s Fuse Box: Refer to your car’s owner’s manual to find the location of the fuse box(es). Common locations include under the dashboard, in the glove compartment, or under the hood in the engine bay.
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Find the Fuse Box Diagram: Inside the fuse box cover, or in your owner’s manual, you’ll find a fuse diagram. This diagram labels each fuse and its corresponding system.
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Identify the OBD2 Fuse: Look for a fuse labeled “OBD,” “Diagnostic,” “Accessory,” or sometimes even “Cigar Lighter” or “Auxiliary.” The OBD2 port is often on a circuit shared with other accessory systems. This is the fuse that powers your OBD2 port.
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Inspect the Fuse: Once you’ve identified the potential fuse, use a fuse puller (often included in the fuse box) or needle-nose pliers to remove it. Inspect the fuse as you did with the cable fuse – look for a broken wire or blackening.
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Test with a Multimeter (Recommended): For a more definitive check, use a multimeter to test the fuse for continuity. A multimeter will confirm if the fuse is indeed blown. Here’s a helpful video on how to check car fuses with a multimeter.
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Replace the Fuse: If the fuse is blown, replace it with a new fuse of the exact same amperage. Using a fuse with a higher amperage can damage your car’s electrical system.
Testing the OBD2 Port for Power with a Multimeter
If you’ve checked all the fuses and still have no power, you can use a digital multimeter to directly test if the OBD2 port is receiving power.
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Set up the Multimeter: Set your multimeter to measure DC Voltage (DCV).
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Locate Pins 16, 4, and 5: On the OBD2 port, locate pin 16 (power), pin 4 (chassis ground), and pin 5 (signal ground). You can find OBD2 port pinout diagrams online if needed.
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Test for Voltage:
- Place the red probe of the multimeter on pin 16 (power).
- Place the black probe on pin 4 (chassis ground) or pin 5 (signal ground).
- Turn your car’s ignition to the “ON” position (you don’t need to start the engine).
- The multimeter should read approximately 12 volts (or your car’s battery voltage).
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Zero Volts Reading: If the multimeter reads 0 volts, even after checking and replacing fuses, there might be a more complex electrical issue, or the OBD2 port itself could be faulty.
Still Having Trouble?
If you’ve gone through all these steps and your OBD2 device is still not powering on, it’s time to seek professional help. Contact a qualified mechanic or your device’s support team for further assistance.
For device-specific support, contact support with details about your vehicle (make, model), the device, and the troubleshooting steps you’ve already taken. This information will help them diagnose the problem more efficiently and get you back on track.
