What fuse powers the OBD port?
The OBD port is powered by a dedicated fuse in the vehicle’s fuse box that feeds pin 16 (the +12V supply) of the OBD‑II connector. The exact fuse and its amperage vary by make and model, but common ratings are 10A or 15A.
In practice, the feed to the OBD port is typically ignition‑switched, so the port powers up when the ignition is on or in the ACC/run position. Some vehicles may keep a constant 12V feed to the port for certain tests, but this is not universal. To identify the precise fuse and location for a specific car, consult the owner’s manual or the fuse diagram on the fuse box cover.
Where the OBD power comes from
The OBD II port receives its power from the car’s 12‑volt electrical system via pin 16, and is protected by a fuse in the vehicle’s fuse box. The ignition/ACC state often controls whether that power is active, meaning the port may require the key to be in RUN or ACC for power to reach the scanner. Because fuse placement and labeling differ among vehicles, locating the exact fuse requires checking the model’s fuse diagram.
Common fuse locations and ratings
There isn’t a single universal location for the OBD power fuse. Most cars place it in one of the standard fuse boxes, and the rating will typically be 10A or 15A, though some models use a smaller 5A fuse for the OBD circuit.
- Under-dash fuse box (driver’s side): Often the most common location, with labels such as OBD, DATA LINK, IGN, or IGNITION on the fuse map.
- Engine bay fuse box: Some vehicles route the OBD feed from a fuse in the engine compartment’s fuse panel, especially on older or larger vehicles.
- Dedicated OBD/diagnostic fuse: A few models use a separate small fuse (often labeled OBD or DIAG) on one of the panels; others may piggyback the feed on the ignition circuit.
Because labeling and layouts vary widely, always refer to your specific vehicle’s fuse diagram or owner’s manual to confirm the exact fuse location and amperage.
How to locate the exact fuse for your vehicle
Follow these steps to identify the OBD power fuse on your car. The process relies on the fuse box layout and labeling for your model.
- Open the fuse boxes and locate the diagrams on the covers or in the owner’s manual; identify fuses labeled OBD, DATA LINK, DIAG, IGN, or IGNITION.
- Check both the under-dash and engine bay fuse panels if you don’t see an obvious OBD label in one box.
- Use a fuse puller to remove suspected fuses and inspect for a blown filament; compare the fuse rating to the diagram.
- If you replace a fuse, install the same amperage as specified for that circuit; do not upsize the fuse to “fix” a power issue.
- Re-test the OBD port with your scanner or a multimeter to confirm power on pin 16 relative to ground.
- If power remains absent after a good fuse and ignition is on, the issue may lie in wiring, the ignition circuit, or the port itself; seek professional service.
Understanding the exact fuse requires model-specific information; incorrect assumptions can lead to electrical problems, so consult official diagrams when possible.
Testing and troubleshooting the OBD power
When diagnosing why an OBD scanner isn’t powering up, check the fuse first, then verify ignition status and voltage at pin 16.
- Verify ignition is in RUN or ACC as required by your vehicle; some ports are live only when the ignition is on.
- Inspect the OBD fuse with a fuse puller and replace if blown, using the same rating.
- Measure voltage at pin 16 relative to a ground reference with a multimeter to confirm when the ignition is on.
- If voltage is present but the scanner does not power, test the scanner on another vehicle or try a different scanner to rule out a faulty tool.
Electrical systems can vary, so when in doubt, consult the vehicle’s service manual or a qualified technician for model‑specific guidance.
Summary
The OBD port is powered through a dedicated fuse in the vehicle’s fuse box that feeds pin 16 with +12V. The exact fuse’s location and rating depend on the car model, most commonly 10A or 15A, and the ignition state often governs whether power is available. Always refer to the owner’s manual or fuse diagram to identify the correct fuse, and follow prudent troubleshooting steps if the port isn’t powering up.
