On-Board Diagnostics (OBD) refers to a computer-based system built into modern vehicles that monitors the performance of major engine and emissions components.

The current standard, OBD-II, is mandatory on most vehicles sold since the late 1990s and features a standardized 16-pin connector port, usually located under the dashboard.

When the vehicle's Electronic Control Module (ECM) detects a problem, it triggers a warning light on the dashboard (like the 'Check Engine' light) and stores a Diagnostic Trouble Code (DTC) in its memory.

This code corresponds to a specific fault.

Using an OBD-II scanner or a telematics device plugged into the port, a technician or fleet manager can retrieve this valuable information: - **Diagnostic Trouble Codes (DTCs):** Pinpoints the specific issue (e.

g.

, 'P0420 - Catalyst System Efficiency Below Threshold').

- **Live Data Streams:** Real-time data from various sensors, such as engine RPM, vehicle speed, coolant temperature, and fuel trim.

- **Freeze Frame Data:** A snapshot of the vehicle's operating conditions at the exact moment a fault code was triggered.

OBD-II is the primary gateway for understanding a vehicle's health, enabling faster troubleshooting and proactive maintenance.