How to Use an OBD2 Scanner to Read and Clear Fault Codes

What Is an OBD2 Scanner?

An OBD2 (On-Board Diagnostics II) scanner is a small device that plugs into a port in your car and reads data directly from the engine control unit (ECU). Every petrol and diesel vehicle manufactured after January 1996 is required by law to have an OBD2 port — which means one scanner works on virtually every modern car, ute, 4WD, or van.

When your check engine light comes on, your car's computer has already logged the reason. An OBD2 scanner retrieves that reason as a fault code — a 5-character code like P0301 — and tells you in plain language what it means. You can also clear the code and turn off the light once you've addressed the issue.

Where Is the OBD2 Port on My Car?

The OBD2 port is almost always located under the dashboard on the driver's side, within 60cm of the steering column. Look for a 16-pin trapezoidal socket, usually black or dark grey.

• Under the steering column (most common)
• Inside the centre console
• Behind a small panel near the handbrake

How to Use an OBD2 Scanner — Step by Step

Step 1: Turn the ignition to ACC or ON
You don't need to start the engine. Turn the key to the accessory or on position so the dash lights up.

Step 2: Plug in the scanner
Insert the scanner into the OBD2 port. It should click in firmly. The scanner will power on automatically.

Step 3: Wait for the scanner to connect
The scanner will detect your vehicle automatically. This usually takes 5–15 seconds.

Step 4: Select Read Codes
Navigate to the Read Codes or Fault Codes option. The scanner will retrieve all stored and pending codes from your ECU.

Step 5: Note your codes
Write down any codes displayed. Common codes include:

• P0300 — Random/multiple cylinder misfire
• P0420 — Catalyst system efficiency below threshold
• P0171 — System too lean (bank 1)
• P0442 — Evaporative emission control system leak

Step 6: Clear the codes
Once you've addressed the fault, select Erase Codes or Clear Codes to reset the check engine light.

Basic vs Advanced OBD2 Scanners

A basic OBD2 scanner reads and clears fault codes — all most people ever need. An advanced scanner also shows live data including engine RPM, coolant temperature, oxygen sensor output, fuel trim, and throttle position. Useful for diagnosing intermittent faults.

• Basic fault code reader — plug in, read the code, clear it. Suits everyday drivers.
• Advanced OBD2 scanner with live data — for mechanics, enthusiasts, and anyone chasing an intermittent fault.

When Should You Take the Car to a Mechanic?

An OBD2 scanner tells you what's wrong — it doesn't fix it. Use the scanner to understand the problem before speaking to a mechanic, verify a repair was completed, and decide if a fault is minor or serious. If you're unsure, don't ignore it.

Shop OBD2 Scanners at Auto Relay

Auto Relay stocks both basic and advanced OBD2 scanners at competitive prices, with fast shipping across Australia.