Diagnostics Scanner
An electronic device plugged into the OBD-II port to read diagnostic trouble codes and view real-time engine sensor data.
A diagnostics scanner (or scan tool) is an electronic device used by automotive technicians to interface with a vehicle's onboard computer systems. It connects to the standardized OBD-II port located under the dashboard. The scanner queries the Engine Control Unit (ECU) and other onboard modules to retrieve Diagnostic Trouble Codes (DTCs), which indicate system faults when the Check Engine light is illuminated.
Scan tools range from basic code readers that display DTC numbers to advanced, professional-grade diagnostic workstations. Advanced scanners can display real-time sensor data (live data stream), perform bi-directional control tests (such as cycling a cooling fan or fuel pump), reprogram modules, and display graphical waveforms of sensor outputs. This data allows technicians to diagnose complex problems rather than blindly replacing parts.
When diagnosing a vehicle, the scan tool is the starting point. It provides clues, such as misfire counts on specific cylinders or out-of-range oxygen sensor voltages. Once repairs are completed, the diagnostic scanner is used to clear the fault codes and monitor the readiness monitors to verify that the vehicle's computer has completed its drive cycle and confirmed the repair.