Which device is used to read vehicle diagnostic codes?

• A. Scan tool
• B. Multimeter
• C. Hydrometer
• D. OBD port

Answer: (A)

Reading vehicle diagnostic codes requires a device that can communicate with the car’s onboard computer to retrieve the codes and translate them into meaningful information. A scan tool is designed for this purpose—it plugs into the OBD port under the dash and talks to the vehicle’s ECU to pull Diagnostic Trouble Codes, show their descriptions, and sometimes display additional data like live sensor readings or freeze-frame information. This makes it the best answer for identifying the exact fault codes and guiding repairs.

A multimeter measures electrical values such as voltage, current, and resistance, which is useful for diagnosing electrical issues but not for reading diagnostic trouble codes from the ECU. A hydrometer measures liquid density, used for fluids like batteries, not for vehicle diagnostics. The OBD port is the physical connector, the interface through which diagnostic data is accessed, but you still need a device (the scan tool) to read and interpret the codes.