What Is OBD-II?

OBD-II (On-Board Diagnostics, version 2) is a standardised vehicle diagnostic system required in all cars and light trucks sold in Australia since 2006 (and in the US since 1996). It monitors your engine, transmission, and emissions systems in real time, and stores fault codes when something goes wrong.

The system uses a 16-pin connector, usually located under the dashboard near the steering column. When a mechanic plugs in a scan tool, they're connecting to OBD-II.

How Does OBD-II Work?

Your car's Engine Control Unit (ECU) continuously reads data from dozens of sensors — oxygen sensors, temperature sensors, pressure sensors, and more. The ECU uses this data to optimise fuel injection, ignition timing, and emissions.

When a sensor reading falls outside its expected range, the ECU logs a Diagnostic Trouble Code (DTC) and typically illuminates the Check Engine Light (CEL) on your dashboard. These codes follow a standardised format across all manufacturers.

What Are Diagnostic Trouble Codes (DTCs)?

DTCs are five-character codes that identify specific faults. The format is:

• First character: System (P = Powertrain, B = Body, C = Chassis, U = Network)
• Second character: 0 = Generic/SAE, 1 = Manufacturer-specific
• Third character: Subsystem (e.g., 1 = Fuel/Air, 3 = Ignition)
• Last two digits: Specific fault number

For example, P0301 means: Powertrain (P), Generic (0), Ignition System (3), Cylinder 1 Misfire (01).

What Data Can You Read from OBD-II?

Beyond fault codes, OBD-II provides real-time sensor data including:

• Engine RPM and vehicle speed
• Coolant temperature
• Fuel system status and fuel trims
• Oxygen sensor readings
• Throttle position
• Intake air temperature and manifold pressure
• Catalyst temperature
• Battery voltage
• And dozens more parameters depending on your vehicle

What Do You Need to Read OBD-II Data?

You need two things: an OBD-II adapter (scanner) and software to interpret the data.

ELM327-based Bluetooth adapters are the most popular consumer option, costing $15–$50 AUD. They plug into the OBD port and wirelessly send data to a phone app.

MyMait connects to ELM327 adapters and uses AI to interpret the data — translating technical codes and sensor readings into plain-English explanations with repair guidance.

OBD-II Port Location

The OBD-II port is a 16-pin D-shaped connector, almost always located in the driver's footwell area. Common locations include:

• Under the dashboard, left of the steering column (most common)
• Under the dashboard, right of the steering column
• Behind a small panel or cover near the fuse box
• Below the handbrake or centre console (some European cars)

If you can't find it, check your owner's manual or search for your specific make and model.