Q: Check engine is on after new alternator

asked by on June 30, 2017

So I get a new alternator and battery. Now check engine light comes on as I'm leaving the shop. I go back to mechanic, he said something about rpm read and memory. Whatever. He gets engine light off. I go get gas. As I'm driving away, car stalls. Engine light comes back on. I turn the car off and on again and it drives halfway home before it stalls completely again. Battery AND check engine light come back on. Turn off for a minute and starts right back up again. Does this 5x before I get home..... HELP this was all in about 15-20min

My car has 114000 miles.
My car has an automatic transmission.

It sounds like you may have a failing voltage regulator. 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. 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. In some cases when a battery is too weak or damaged, it may no longer hold a charge for any length of time, in which case the alternator may be doing its job, but the battery is just simply too weak to hold a charge. In either case, I would recommend having an expert from YourMechanic come to your location to diagnose your vehicle’s charging system.

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