Which component is used for engine start if battery voltage is insufficient?

• A. Generator
• B. External Power Unit (EPU)
• C. GCU
• D. Starter generator

Answer: (B)

When the battery can’t supply enough current to turn the starter, you need a separate, strong power source to crank the engine. That’s what the External Power Unit does: it provides the necessary electrical power at the correct voltage to run the starter motor until the engine starts and can take over with its own power. A generator or starter generator is meant to supply power once the engine is already turning and running, not to jump-start the engine when the battery is too weak. The GCU is a control unit, not a power source. So the External Power Unit is the right choice for starting the engine when battery voltage is insufficient.