Which tool is commonly used to retrieve diagnostic trouble codes from a bus's electronic control units?

• A. A diagnostic scan tool or bus-specific code reader.
• B. A standard multimeter.
• C. A torque wrench.
• D. A battery tester.

Answer: (A)

Reading diagnostic trouble codes requires a tool that talks to the bus ECUs over the vehicle’s diagnostic network. A diagnostic scan tool or bus-specific code reader plugs into the bus port, communicates with the electronic control units, and retrieves the stored DTCs, often showing code descriptions, freeze-frame data, and current status. This is how technicians quickly pinpoint faults across the bus’s electronic systems.

A standard multimeter measures electrical values like voltage or resistance but does not access or interpret the ECU fault codes. A torque wrench is for tightening fasteners to a specification, and a battery tester checks battery health—not diagnostic fault data from the control units.