A diagnostic system for an active fuel management (AFM) solenoid of an internal combustion engine is provided. The system includes: a command module that selectively commands a solenoid signal to energize and de-energize the AFM solenoid, a timer module that activates a timer based on a status of the solenoid signal, and a fault module that selectively diagnoses a fault of the AFM solenoid based on the timer and a knock sensor signal.