Every check engine light starts with the same question: what is my car trying to tell me? An OBD2 scanner answers that in under two minutes. Here's exactly how to use one, even if you've never opened a hood.
Step 1: Find the port
The OBD2 port is a 16-pin trapezoid connector, almost always under the dashboard on the driver's side within arm's reach of the steering wheel. Some cars hide it behind a small flap, in the centre console, or near the fuse box. Every car from 1996 (US) / 2001 (EU petrol) has one – see our compatibility guide.
Step 2: Plug in and read
- Turn the ignition to ON (engine can be off for reading codes).
- Plug in the scanner – handhelds power up from the port; Bluetooth adapters pair with their phone app.
- Select Read Codes. You'll see one or more codes like P0420 or P0171.
Step 3: Understand the code
The first letter tells you the system: P = powertrain (engine/transmission), B = body, C = chassis, U = network. The numbers narrow down the exact fault. Look the code up in our fault code guides or on the CarCodes YouTube channel – we cover the causes from cheapest to most expensive, so you never replace a $900 part when a $20 sensor cleaning would have done it.
Step 4: Fix first, then clear
Clearing a code just turns the light off – it doesn't repair anything. Fix the cause, then use Erase Codes, and drive a few days. If the light stays off, you're done. If it returns, the freeze-frame data (a snapshot of conditions when the fault occurred) will help you dig deeper.
Which scanner do you need?
- Basic: reads and clears engine codes – enough for most check engine lights.
- Mid-range: adds live data and freeze frame – lets you diagnose like the guides show.
- Advanced: reads ABS, airbag and transmission modules too.
Browse the scanners we use in our videos – each one links back to the matching guides.