The starter control system prevents the starter from accidentally activating when the shift lever is not in the P or N position (A/T) or the clutch pedal is released (M/T), or when the engine is running. If the engine start/stop button is pressed mistakenly while the shift lever is not in P or N position (A/T) or the clutch pedal is released (M/T) or while the engine is running, the powertrain control module (PCM) will stop power to the starter cut relays. In this system, two starter cut relays are connected in series (starter cut relay 1 circuit, starter cut relay 2 circuit) to prevent the starter from running continuously due to a starter cut relay malfunction. Also a diagnosis line (ST RLY 1 TO 2) is connected to monitor the voltage between the starter cut relay 1 circuit and starter cut relay 2 circuit. Based on the diagnosis line signals, the PCM detects an OPEN malfunction of diagnosis line, an ON malfunction of starter cut relay 1 circuit, and an ON malfunction of starter cut relay 2 circuit. If the voltage of the diagnosis line (ST RLY 1 TO 2) input does not exceed the upper and lower limits for a specified duration when the power is applied to the starter cut relays by engine start/stop button to select the START mode (STS ON), the PCM detects an OPEN malfunction of the diagnosis line and stores a DTC.