Which of the following statements about fault code retrieval are correct?

• A. Both reading by blink codes and using a diagnostic switch
• B. Only reading by blink codes
• C. Only using a diagnostic switch
• D. Neither

Answer: (A)

Fault code retrieval relies on accessing stored diagnostic trouble codes to pinpoint issues. Two common ways to get those codes are reading blink codes and using a diagnostic switch.

Reading blink codes works by watching a warning light—often the check engine light—that flashes in a specific pattern. Each sequence of blinks represents a particular code, and you translate the pattern to identify the fault. This method is handy on older systems or when a dedicated tool isn’t available, because it communicates the needed information directly through the light.

Using a diagnostic switch involves activating a mode in the control module that causes it to output the codes in a readable form, such as flashing a sequence with indicators or displaying digits on a dashboard display or odometer. This method provides another built-in route to access the codes without external equipment.

Some vehicles support either method, or both, giving technicians flexible options for diagnosing issues. That’s why the statement that both reading blink codes and using a diagnostic switch are correct is the best choice.