Lauren HollandBy Lauren Holland

Updated November 2026

An obd1 and obd2 scanner is the tool you need to read trouble codes from your car, but only if it speaks the right protocol. OBD1 was used on many cars from the late 1980s through the mid-1990s, while OBD2 became mandatory in the United States for all gasoline vehicles starting with 1996 models. By the end of this guide, you will know which system your car uses, how to connect a scanner correctly, and what to do with the codes you pull.

Step 1: Find Out Which System Your Car Uses

Start by checking the model year. Most cars sold in the US from 1996 onward use OBD2, and the diagnostic port is a 16-pin trapezoid connector, usually under the dash on the driver’s side. Cars from roughly 1981 to 1995 may use OBD1, which relied on a variety of proprietary connectors, some with 3 to 20 pins, and often required a manufacturer-specific scan tool or a jumper wire to flash codes on a check engine light.

Shopping for one? See our guide: 3 Best OBD2 Scanners for Nissan Rogue Compared (2026).

Keep in mind that some 1994 and 1995 vehicles were transitional. Manufacturers such as General Motors and Ford used OBD1 on some models and OBD2-style connectors on others, so check your owner’s manual or a repair database before buying a tool.

Step 2: Match the Scanner to the Port

An OBD2 scanner will not communicate with an OBD1 car, and most OBD1 connectors will not accept an OBD2 plug. For OBD1 vehicles, you will generally need one of the following:

  • A dedicated OBD1 adapter or breakout box that fits your manufacturer’s connector
  • A manufacturer-specific code reader for older GM, Ford, Chrysler or Honda systems
  • A manual flash procedure, where you jump two terminals on the diagnostic connector and count blinks on the check engine light

For OBD2 vehicles, nearly any scanner with the standard 16-pin plug will work. Look for support for the ISO 15765 (CAN) protocol, which covers nearly all cars from 2008 onward.

Step 3: Read and Record the Codes

With the ignition off, plug the scanner into the port, then turn the key to the on position without starting the engine. Follow the scanner prompts to read stored and pending codes. Write down every code exactly as shown, including the letter prefix:

  1. P codes relate to powertrain, including engine, transmission and emissions.
  2. B codes cover body systems such as airbags and climate control.
  3. C codes cover chassis, including ABS and steering.
  4. U codes indicate network or communication faults between modules.

Pending codes are faults the computer has detected once but not yet confirmed. They are useful early warnings even if the check engine light is off.

Step 4: Check Freeze Frame Data Before Clearing Anything

Freeze frame data is a snapshot of sensor values recorded when a fault was set, such as engine speed, coolant temperature and fuel trim. Save or photograph this data before you clear codes. Clearing codes erases freeze frame data, and you lose the clues that help identify intermittent problems. Clearing codes also resets readiness monitors, so an emissions test may fail until the monitors complete their drive cycles.

Common Mistakes and Tips

  • Do not clear a code without knowing its cause. A cleared code that returns within a few drive cycles means the fault is still present.
  • Check the fuel cap and loose vacuum hoses before replacing expensive parts. A loose gas cap commonly triggers evaporative emission codes.
  • Use a Bluetooth or wired scanner with live data if you want to watch sensors in real time, such as oxygen sensor voltage or coolant temperature.
  • If you have an OBD1 car, verify the connector type before buying anything. Mismatched adapters can damage the port or the module.

A basic OBD2 code reader covers most home diagnostics on post-1996 vehicles and keeps the process simple: View on Amazon

For owners who want live sensor graphs and a phone display, a Bluetooth adapter paired with a smartphone app is a practical choice: View on Amazon

If you are working on an older vehicle, look for an OBD1-compatible breakout kit that matches your manufacturer’s connector: View on Amazon

For more detail on specific vehicles and scanner types, see OBD2 Scanners and Code Readers: What They Can and Cannot Tell You, Wireless Bluetooth OBD2 Scanner: How to Pick and Use One at Home, and Obd2 Scanner for Trucks: How to Read and Clear Codes Yourself.

FAQ

Can an OBD2 scanner read an OBD1 car?

Generally no. OBD1 used different connectors and communication methods, so you need an OBD1-specific adapter or a manufacturer-specific reader for those vehicles.

How do I know if my car is OBD1 or OBD2?

Cars sold in the US from 1996 onward use a 16-pin OBD2 port. Older vehicles, and some transitional 1994 and 1995 models, may use OBD1 connectors, so check your owner’s manual or a repair database.

Will clearing codes fix the problem?

No. Clearing codes only removes the warning light and stored data. If the underlying fault is still present, the code will usually return. For safety-related systems such as brakes or airbags, consult a qualified professional.

Conclusion

Confirm your car’s diagnostic system before buying any tool, and make sure the scanner matches the port. Record codes and freeze frame data before you clear anything. With those steps, you can handle many common faults at home and know when to hand a problem to a shop.

Ready to choose one?

Lauren Holland

About Lauren Holland

Lauren Holland is part of our editorial team and reviews and edits our car care & garage supplies guides, checking product details against manufacturer specifications and owner feedback.