Vehicle charging systems consist of the alternator, a regulator that is often located inside the alternator, and interconnecting cables. This system maintains the charge in the vehicle’s battery and carries the main source of electrical power while the engine is running. If the charging system is not working properly, the battery can be discharged quickly. If there is a “dead battery” condition and an improperly functioning alternator, the engine will stop running.
Setting the P2505 OBDII diagnostic code indicates that the battery voltage has been below 10V for more than 8 seconds so the Check Engine light will turn on.