What is on-board diagnostics (OBD)?

HomeGlossary of fleet termsWhat is on-board diagnostics (OBD)?

On-board diagnostics (OBD) definition

On-board diagnostics (OBD) rely on sensors to detect issues with different vehicle components. The sensors communicate with an embedded computer system in the vehicle. Most drivers see the results of these sensors and computer functions via the dashboard. Malfunction indicator lights (MILs), such as the check engine icon, are triggered by the OBD system.

Modern vehicles have sensors for everything from oil levels to fuel injection systems to tire pressure. OBD computers collect data on specifics of vehicle performance and functions. While this info doesn’t show up on the dashboard, you can use a scanner to get diagnostic trouble codes (DTCs), which can provide specifics to help you focus repair or maintenance efforts.

Here is a look at how OBD systems work and the benefits they can provide in cost reduction, safety and compliance with emissions and safety rules.

How does OBD work?

The OBD system has sensors that continuously monitor the vehicle’s critical systems and components. The data gets sent to the electronic control module (ECM), which is essentially the car’s on-board computer. It can control engine functions and generate alerts and diagnostic trouble codes.

Here is a closer look at the different components of the system.

  • Electronic control units process the information for the OBD system. The ECU has two jobs. It manages the engine, transmission, braking and other car functions. Also, it collects performance data, sends malfunction alerts to the malfunction indicator light system and generates diagnostic trouble codes.
  • Sensors measure parameters such as engine temperature, air intake, exhaust, tire pressure, traction and vehicle speed and provide data to the electronic control unit.
  • Actuators are responsible for moving and controlling different vehicle systems and carrying out commands from the electronic control unit. For instance, actuators adjust fuel injectors and throttle valves to achieve optimal engine performance.
  • Malfunction indicator lights display icons that let the driver know about a problem. These icons can track everything from oil levels to engine function. They are not meant to serve as diagnostic tools, but rather to warn the driver to get maintenance as soon as possible.
  • A diagnostic link connector (DLC) is the interface diagnostic tools such as OBD scanners use to connect to the system to retrieve diagnostic trouble codes. Though drivers with the right device can use this link themselves, it is usually mechanics who check malfunction indicator light alerts by plugging a sensor into the DLC.
  • OBD-II sensors display diagnostic trouble codes after connecting to the diagnostic link connector. These devices are available in hand-held form, though technicians and auto garages may have larger units that display more information and run other software that supports the diagnostic and repair process.

While OBD was initially designed to monitor the performance of major engine components, it has evolved over the years. Today, the system manages safety features and measures emissions.

This evolution has led to two different on-board systems: OBD-I and OBD-II.


OBD-I and OBD-II are two generations of onboard diagnostics systems. The key differences between OBD-I and OBD-II include standardization, level of integration and legal requirements.

The first-generation OBD-I was used until the mid-90s. OBD-I was primarily for monitoring emissions control systems for regulation. However, OBD-I was not standardized. Interpreting diagnostics was complex, and you often needed specific tools for different vehicle brands. OBD-II emerged in the mid-1990s to provide more accurate emissions readings. Unlike OBD-I, it was standardized according to rules set by the Environmental Protection Agency.

OBD-II also boasted improved integration and uniformity, featuring standardized connectors, making it easier for technicians to access and diagnose vehicle systems for all brands with the same scanners. OBD-II also expanded beyond emissions control to monitor engines, brakes, and other functions and provide detailed trouble codes. Because of its effectiveness, OBD-II became mandatory for all vehicles sold in the U.S. from the 1996 model year onwards.

What can OBD be used for?

OBD provides a wide range of data about a vehicle’s performance and efficiency, which can be accessed through the standardized OBD port. Some types of information accessible through OBD include engine RPM, fuel system status, oxygen sensor readings, coolant temperature, vehicle speed and emission control system data. This information can be used for different purposes.

  • Driver behavior monitoring: OBD data can track and analyze driver behavior, including speed, acceleration and braking. This information is valuable for assessing driver safety and encouraging responsible driving habits.
  • Emissions control: OBD plays a crucial role in emissions testing. It ensures vehicles comply with environmental standards by monitoring emissions-related components and systems.
  • Supplementary instrumentation: OBD data can inform customized displays. For instance, a car’s infotainment system or dashboard display can show real-time data on fuel efficiency. Driving enthusiasts and professional drivers often use OBD systems to view metrics that lead to subtle performance improvements.
  • Telematics: Telematics systems can collect and transmit OBD data and enable remote vehicle tracking and real-time diagnostics. These functions are valuable for business fleet management, insurance policy pricing and vehicle owners seeking insights into their driving habits. You can install an OEM telematics platform to add the necessary functions for fleet management.
  • Maintenance and repairs: Technicians can use OBD data to diagnose and identify issues quickly, reducing repair time and costs and improving diagnostic accuracy.

OBD scanners are available to drivers who want to see diagnostic trouble codes and other performance data for DIY repairs or a better idea of repair costs.

The benefits of OBD for fleet management

On-board diagnostics can streamline fleet management, lower repair costs, and make compliance with clean-air and safety standards much easier. With the addition of tools like GPS fleet tracking software, you can focus on effectively managing every aspect of your company’s fleet.

Here are three of the most important benefits of OBDs.

Improved diagnostics

OBD accelerates diagnostics by giving mechanics more information about potential problems with the vehicle. They can then target the area needing repair more accurately than if they just looked at the dashboard malfunction indicator lights.

The diagnostic trouble codes can reveal issues before they lead to a major breakdown, allowing preventative repairs. Early diagnosis can also help keep fleet autos in optimal working order and operating at peak efficiency.

Improved compliance

From 2027 to 2032, the Environmental Protection Agency plans to roll out increasingly strict emissions requirements for light-duty and medium-duty vehicles, making exhaust monitoring even more important. By continuously scanning emissions-related components, OBD ensures that vehicles are operating within acceptable limits. When a vehicle falls outside the acceptable standards, mechanics can use diagnostic trouble codes to find and correct the issue.

This proactive approach helps organizations avoid penalties, ensuring they meet emission standards consistently.

Reduced costs

Accurate diagnostics, made possible by OBD, minimize downtime and create a more efficient repair process by enabling faster identification and resolution of issues. With this system in place, vehicles spend less time in the repair shop and can avoid undiagnosed problems leading to costly repairs.

The OBD system’s role in compliance management helps fleets avoid fines associated with environmental regulations. By consistently meeting emission standards, organizations can avoid costly penalties that could erase profits.

Vehicle owners can further reduce fuel and vehicle replacement costs by pairing their onboard diagnostics with GPS asset tracking to manage maintenance of high-value equipment, route that equipment more efficiently to work sites, and generally improve utilization.

On-board diagnostics are a necessary component of a fleet management system. They lead to speedier repairs and help you avoid expensive maintenance issues. These systems can ensure compliance with emissions standards and give you the data necessary to operate at peak efficiency and track vehicles in near real time.

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