Plug an automotive diagnostic scanner into the 16-pin OBD-II port under the dash, turn the ignition to ON, then read the codes on your screen.
For the full breakdown, see our best Automotive Scanner guide.
Modern cars translate most breakdowns into diagnostic trouble codes, and knowing how to use automotive diagnostic scanners turns a glowing check-engine light into a specific answer. The procedure is nearly identical across brands: plug the tool into the vehicle’s 16-pin OBD-II port, turn the ignition to ON, and let the scanner’s menu walk you through the rest. A handheld unit or a phone app changes the buttons, not the order of operations.
What You Need Before Plugging In
Before any diagnostic work you need three things: a scanner, a compatible vehicle, and access to the port. Gasoline vehicles sold in the US since 1996 carry a standard 16-pin Data Link Connector (DLC), almost always under the dash on the driver’s side. It can sit behind a small panel, near the hood release, or above the pedals; the owner’s manual gives the exact spot.
Scanners come in two broad families. Handheld units do the job on their own screen, while Bluetooth OBD-II adapters turn a phone into the display. Which family you choose determines the setup steps, so the comparison matters:
| Scanner Type | What It Does | Typical Price |
|---|---|---|
| Basic code reader | Reads and clears engine (powertrain) codes and shows plain-language descriptions. | $20 – $100 |
| Bluetooth adapter + phone app | Reads codes and graphs live data on a phone; some apps add ABS and airbag coverage. | $25 – $150 |
| Professional handheld tool | Covers all vehicle systems, with active tests, service resets, and coding functions. | $450 – several thousand |
If you’re still deciding which tier fits your garage, our tested lineup of the best automotive scanners compares the main options head to head.
Reading Codes: The Automotive Diagnostic Scanner Hookup Sequence
The hookup follows five moves that are close to identical on every scanner sold today. Menu wording varies by brand, but the order does not: connector