Q: 2012 Jeep Grand Cherokee replaces altanator, still won’t start. Brake seems locked

The brakes may feel stiff prior to starting the vehicle as the vacuum that exists in the brake booster when the vehicle is running may decrease when the vehicle is not running. Once the vehicle starts, the booster replenishes the vacuum assist and the brake pedal should feel normal again.

The issue of the vehicle not starting after charging the battery or after it sits for a period of time may suggest a failing voltage regulator that could be allowing the alternator to supply too much or too little amperage to the battery resulting in the battery never maintaining a consistent charge as it is designed to. The voltage regulator is a unit that regulates the charging of the battery by the alternator. When the voltage regulator is not working properly, this may result in the alternator allowing too much power to be delivered to the battery resulting in damaging wires and prematurely sometimes destroying the battery. A common sign of this is usually the acid inside the battery boiling causing the battery to swell. You may also smell a bit of smoke due to things potentially getting too hot. In other cases it may result in the alternator not supplying enough power to the battery, resulting in undercharging the battery or not charging it at all. I would recommend having an expert from YourMechanic come to your location to diagnose your vehicle’s charging system.