Discovering your OBD2 port has no power can be a frustrating setback, especially when you need to diagnose a Check Engine Light or perform essential vehicle scans. If your OBD2 scanner is failing to power up when connected to your car, don’t worry. Often, the issue is simpler than you might think. This guide will walk you through the most common cause – a blown fuse – and how to quickly check and resolve it, getting you back to diagnosing your vehicle in no time.
The first and easiest step in diagnosing a powerless OBD2 port is to check Fuse 13, typically located in your vehicle’s underhood fuse box. This fuse often powers both the OBD2 port and the cigarette lighter (or accessory power outlet). A seemingly functional cigarette lighter can sometimes mislead you, as it might still receive a partial voltage even with a failing Fuse 13.
To begin, locate the underhood fuse box. Your owner’s manual will have a diagram indicating its exact location and fuse layout. Once you’ve found it, identify Fuse 13. Even if the fuse appears visually intact, it’s crucial to replace it with a known good 20 Amp fuse. Fuses can sometimes be defective internally or have poor terminal connections due to dirt or oxidation, even if they don’t look blown.
Image: Diagram illustrating the location of Fuse 13 within a typical underhood fuse box, highlighting its connection to the OBD2 port and cigarette lighter.
After replacing Fuse 13 with a new fuse, test your OBD2 port again. Plug in your OBD2 scanner to see if it now powers on. While you’re at it, check your cigarette lighter port as well to see if it’s now functioning correctly with a full 12V reading.
If replacing Fuse 13 doesn’t solve the problem and your OBD2 port still has no power, further diagnosis with a multimeter is necessary. Set your multimeter to the DC Volts setting. Ground the negative (black) lead of the multimeter to a suitable ground point in your vehicle. With Fuse 13 installed, use the positive (red) probe to touch each of the exposed metal contacts on top of Fuse 13. You should see a 12V reading on both sides of the fuse.
Image: Illustration showing how to use a multimeter to test Fuse 13 for voltage, demonstrating the probing of both fuse terminals to ensure power flow.
If you are not reading 12V on both sides of Fuse 13, switch your multimeter to Ohms (resistance) mode. Remove Fuse 13. Connect one multimeter lead to the load side contact of Fuse 13 in the fuse box (the side that did not read 12V). Connect the other lead to Pin 16 of your OBD2 port. You should read close to zero ohms, indicating good continuity in the wiring. If you don’t see near zero ohms, there is likely a break or issue in the wiring between the fuse box and the OBD2 port, requiring further tracing and potential repair of the wire.
This troubleshooting process should help you pinpoint why your OBD2 port is not receiving power. Starting with the simple fuse replacement can often resolve the issue quickly. If the problem persists, using a multimeter to check voltage and continuity will help you further isolate the fault, whether it’s a fuse issue, wiring problem, or something else. Remember to consult a professional mechanic if you are uncomfortable with electrical testing or cannot locate the source of the problem.
