How to use WOBD

Everything you need to go from "my check engine light is on" to a plain-English answer.

1. What you need

A car with OBD-II. In the US, that's every car and light truck from model year 1996 on.
A USB ELM327-compatible adapter. See the next section.
A Chromebook or laptop running Chrome, Edge, or Opera. Firefox, Safari, and phones can't talk to the adapter.

2. How to get an adapter

OBD-II adapters are sold at auto parts stores and online. When you shop:

Buy a USB cable adapter, not Bluetooth or Wi-Fi.
Check that it says ELM327-compatible.

We'll list adapters confirmed to work with WOBD here once testing is done.

3. Finding the OBD port

The port is under the dashboard on the driver's side, within reach of the steering wheel. It's a 16-pin, trapezoid-shaped plug, sometimes behind a small cover.

Look below the dashboard, near your left knee. On some cars it's behind a small panel.

4. Using the site

Plug the adapter into the car and into your computer.
Turn the ignition on. The engine can stay off.
Open WOBD and click Connect, then pick your adapter from the list.
Tell Bob your car's year, make, and model, or click Skip.
Click Scan.
Click any code to hear what Bob has to say about it.
Use Print report to take the results to a shop. Choose "Save as PDF" in the print dialog to keep a copy.

5. Live data

Open the Live data tab to see real-time readings from the engine. Only watch it while parked or from the passenger seat.

Engine RPM: how fast the engine is turning. A warm engine usually idles between 600 and 900.
Speed: the speed the car's computer sees.
Coolant temp: engine temperature. Most engines run around 195 to 220 °F once warm.
Engine load: how hard the engine is working, as a percentage.
Throttle: how far the throttle is open.
Battery: voltage at the OBD port. About 12.4 to 12.7 V with the engine off, and 13.5 to 14.7 V running.

6. Clearing codes

Clear codes after a repair to turn off the check engine light. If the problem isn't really fixed, the light will come back.

Don't clear codes right before an emissions inspection. Clearing also resets the car's readiness monitors, and the car has to be driven for a while before it's ready to pass again.

7. Troubleshooting

The adapter doesn't appear in the Connect list: unplug and reseat the cable, or try another USB port.
"Unable to connect": make sure the ignition is on and the adapter is pushed all the way into the car's port.
The page won't connect in Firefox or Safari: those browsers can't talk to USB adapters. Switch to Chrome or Edge.