Experiencing a dead OBD2 port in your 2004 GMC can be frustrating, especially when you need to diagnose engine issues. A non-functional OBD2 port means your scan tool won’t be able to communicate with your vehicle’s computer, leaving you in the dark about potential problems. Often, the culprit is simpler than you might think – a blown fuse. Let’s walk through a straightforward fix and some further diagnostic steps if needed.
The first and easiest thing to check is Fuse 13 in your underhood fuse box. This fuse is often responsible for powering both the OBD2 port and the cigarette lighter (or auxiliary power outlet). Sometimes fuses can appear visually intact even when they are blown, or they might have internal defects. Additionally, corrosion or dirt on the fuse terminals can also cause issues.
Replacing Fuse 13 with a new 20 Amp fuse is a quick and inexpensive first step. After replacement, check if your OBD2 port is now working by plugging in your scan tool. Also, verify if your cigarette lighter port now registers approximately 12VDC. If replacing the fuse solves the problem, you’re in luck! It might have been just a faulty fuse.
If you’re still facing a lack of power after replacing Fuse 13, the next step involves using a multimeter. Set your multimeter to read DC Volts. Ground the negative (black) lead of the multimeter to a suitable ground point on the vehicle. With Fuse 13 installed, use the positive (red) lead to probe both exposed metal contacts on the top of Fuse 13. You should see a reading of approximately 12VDC on both sides of the fuse. If you don’t see 12VDC on both sides, this indicates a problem with the power supply to the fuse box itself, which is less common but possible.
If you only see voltage on one side of Fuse 13, or no voltage at all, switch your multimeter to Ohms (resistance). Disconnect the negative lead from the battery for safety. Place one probe of your multimeter on the side of the Fuse 13 socket that showed no voltage (the load side). Then, touch the other probe to pin 16 of your OBD2 port. You should ideally see a reading close to zero ohms, indicating good continuity in the wire. If you see high resistance or an open circuit (infinite resistance), there’s likely a break or fault in the wiring between the fuse box and the OBD2 port. Tracing this wiring will then be necessary to locate and repair the break.
This troubleshooting process should help you pinpoint the reason for no power at your 2004 GMC’s OBD2 port. Starting with the fuse is always the simplest and most frequent solution. If it’s not just the fuse, systematically checking with a multimeter will help isolate whether the issue is before the fuse box, at the fuse itself, or in the wiring leading to the OBD2 port. Once you restore power, you can then use your OBD2 scanner to read any diagnostic trouble codes and proceed with further repairs as needed.
