What is an OBD-II port?

An On-Board Diagnostics version two (OBD-II) port is a standardized diagnostic interface included in nearly all vehicles made in or after 1996, which is when the OBD-II specification was made mandatory for all cars sold in the United States.

OBD-II ports communicate with the vehicle’s on-board computer system to retrieve data, including engine speed, fuel consumption, cylinder performance, intake air temperature, and much more. Included in this data can be fault codes, known as DTCs, which are set by the vehicle’s computer system when a fault is detected with a particular component.

What is a DTC?

DTC stands for Diagnostic Trouble Code. It is a code generated by a vehicle’s on-board diagnostic (OBD) system when it detects a malfunction or problem within a specific system or subsystem of a vehicle. DTCs are standardized across various makes and models of vehicles, and while all vehicles produced must support a specific subset of these codes if they use an OBD-II port, manufacturers also have additional codes, including some that may be specific to their vehicles.

How do I know what problem a DTC has detected?

Each DTC fault code is made up of five characters: A single letter followed by four numbers. The letter denotes which of the four main systems the fault has been detected in:

  • P: Powertrain
  • B: Body
  • C: Chassis
  • N: Network

The second character is a number that specifies whether it’s a generic OBD-II code or a manufacturer code. (Manufacturers reserve the right to generate their own codes if there isn’t a generic code for a specific problem they’d like drivers/techs to be able to diagnose.)

  • 0: Standardized (SAE) fault codes
  • 1: Manufacturer-specific codes

The third character is either a letter or number that specifies which of the vehicle systems is throwing a fault:

  • 0: Fuel and air metering and auxiliary emissions controls
  • 1: Fuel and air metering
  • 2: Fuel and air metering (specific injector circuit)
  • 3: Ignition systems or misfires
  • 4: Auxiliary emission controls
  • 5: Vehicle speed control and idle control systems
  • 7, 8, 9: Transmission and gearbox faults
  • A, B, C: Hybrid propulsion systems

The fourth and fifth numbers denote the specific fault being detected. It can be any number between zero and 99.

Nearly all modern OBD-II scanners will summarize what the error code is alongside the five-character alphanumeric code. For some of the more advanced models, there’s even a code look-up function that will further explain what the fault code is referring to and what might be causing it.

In the case of the Bluetooth OBD-II scanners, some of the apps will also include video explainers pulled from YouTube that will show you how to further diagnose and even repair the faulty components responsible for the code.

Where is my OBD-II port located?

Although the exact location of the OBD-II port can vary from vehicle to vehicle, the port is typically located around the footwell on the driver’s side, beneath the steering wheel and above the pedals.

Why Trust Us

This test was conducted in an environment that provided equal testing procedures for each product: the Car and Driver garage. We tested each OBD-II scanner equally to compare them based on time to display code, cord length, user interface, and more. Upon tallying our findings, we agreed that our test provided enough information to recommend picks to our readers.

Hearst Autos combines the talent, resources, and expertise of three of the largest, most influential automotive publications in the world. We don’t need to game SEO algorithms for traffic, or promote lousy products to make a sale. We’re far more concerned with our legacy, our reputation, and the trust that our readers have in Autoweek, Car and Driver, and Road & Track to deliver honest evaluations and expert opinions.

Read more about our product testing and evaluation process here.


By admin