If you’re plugging a device into your OBD2 port and it’s not powering on, it can be frustrating. Typically, a device will beep or light up to indicate it’s receiving power from the OBD2 port. When this doesn’t happen, and you’ve already checked and confirmed that your car’s fuses related to the OBD2 port are in good condition, you might be wondering what the next steps are. This guide will walk you through troubleshooting steps to diagnose why your OBD2 port isn’t providing power, even when the fuses seem to be fine.
Initial Connection Checks
The most straightforward issues are often related to poor connections. Before diving deeper, ensure everything is properly connected.
Direct OBD2 Device Connection
If you are connecting your device directly to the OBD2 port, the first step is to simply unplug it and firmly plug it back in. Sometimes, a device may seem connected but isn’t making full contact with the port’s pins. A loose connection can prevent power from reaching your device.
Using an OBD2 Extension Cable
Extension cables can introduce additional points of failure. If you’re using an OBD2 extension cable with your device, try these checks:
Check the Cable Connection to the OBD2 Port
- Turn off your vehicle’s engine.
- Disconnect the extension cable from the vehicle’s OBD2 port.
- Wait for a few minutes, then firmly reconnect the cable.
- Listen for your OBD2 device to beep or indicate power. If it does, the issue might have been a loose connection at the OBD2 port itself.
Check the Cable Connection to the OBD2 Device
If you still don’t get a power indication:
- Ensure the engine is off.
- Disconnect your OBD2 device from the extension cable.
- Wait a few minutes before plugging the device back into the extension cable.
- Again, listen for any power-on signal from your device. This step helps rule out a poor connection between the cable and your device.
Test the OBD2 Device Directly
To isolate whether the problem is with the cable or the device itself, try connecting your OBD2 device directly to the vehicle’s OBD2 port, bypassing the extension cable entirely. If the device powers on when directly connected, then the issue is likely with the extension cable or its fuse (if it has one).
Re-examining Fuses – Even if They Look OK
Even if you’ve checked your fuses and they appear to be intact, it’s worth a closer look. Sometimes, fuses can have hairline fractures that are hard to spot visually but still prevent current flow.
- Physically remove and inspect each fuse related to the auxiliary power or cigarette lighter circuit (which often powers the OBD2 port). Hold them up to a light source to check for any breaks in the internal wire.
- Try swapping the fuse with a known good fuse of the same amperage rating. This is a quick way to rule out a faulty fuse that might be visually deceiving. Refer to your vehicle’s owner’s manual for the fuse box location and the correct fuses to check.
Testing OBD2 Port Power with a Multimeter
For a definitive diagnosis, use a digital multimeter to test if the OBD2 port is actually receiving power. This will confirm whether the issue lies with the port itself or further upstream in the vehicle’s electrical system.
-
Set your multimeter to measure DC Voltage. A 20V setting is usually appropriate for automotive circuits.
-
Locate pins 16, 4, and 5 on your OBD2 port. Pin 16 is the positive power pin, and pins 4 and 5 are ground pins. You can find diagrams of the OBD2 port pinout online if you’re unsure of their location.
-
Connect the red lead (positive) of your multimeter to pin 16.
-
Connect the black lead (negative/ground) of your multimeter to pin 4 or pin 5.
-
Turn your vehicle’s ignition to the “ON” position (you don’t need to start the engine, but the ignition should be on to power the accessory circuits).
-
Read the voltage on the multimeter. You should typically see a reading close to 12V (or your vehicle’s battery voltage).
- If you read approximately 12V: The OBD2 port is receiving power. The problem might be with your OBD2 device itself, or a compatibility issue.
- If you read 0V: The OBD2 port is not receiving power. Since you’ve checked the fuses, this could indicate a wiring issue between the fuse box and the OBD2 port, or a problem with the port itself.
Checking Ground Connections
While pin 16 provides power, a proper ground connection is equally crucial. If there’s an issue with the ground, the circuit won’t be complete, and your device won’t power on.
- Test continuity to ground: With your multimeter in continuity mode (or resistance mode), check for a good ground connection at pins 4 and 5. Connect one lead to pin 4 (or 5) and the other to a known good chassis ground point on the vehicle (unpainted metal part of the frame). You should get a continuity beep or a very low resistance reading, indicating a good ground.
Internal OBD2 Port Issues
In rare cases, the OBD2 port itself might be damaged internally. Pins can become bent, corroded, or pushed out of position, preventing proper contact.
- Visually inspect the OBD2 port for any signs of damage or corrosion.
- Gently try to wiggle each pin to see if any are loose or feel different from the others. However, be careful not to damage them further.
Still No Power?
If you’ve gone through all these steps and your OBD2 port still seems to have no power, even with good fuses, it’s time to consider more complex issues. There could be a break in the wiring harness between the fuse box and the OBD2 port, or a fault within the vehicle’s Body Control Module (BCM) if it controls power to the OBD2 port.
At this stage, it’s often best to consult a qualified automotive electrician or mechanic. They have specialized tools and knowledge to diagnose more intricate electrical problems.
If you are using a device from a specific vendor and suspect device malfunction, contacting their support can also be beneficial to rule out device-specific issues before seeking professional automotive repair.
