Would it be the starter or alternator?
My car has 140000 miles.
My car has an automatic transmission.
A dead alternator will not prevent the engine from starting. As long as the car battery is FULLY charged and not defective, the battery alone provides all of the power required for ignition and starting. However, a dead alternator will, of course, not re-charge a battery and the battery will slowly die once you run a car with a dead alternator. Consequently, once the car is running normally, be sure that the charging output is tested by a certified mechanic. "New" batteries sold by stores are not necessarily fully charged so you "could" have a discharged battery. Before doing any further diagnostics, have the battery fully charged. Be sure any engine immobilizer system (security system) is not activated, thus preventing the car from starting. Broadly, if the immobilizer is off, and the battery is fully charged, either the starter motor/solenoid assembly is faulty or the electrical circuit supplying the motor has a fault. That circuit begins at the battery and includes grounds, wiring (some of which is very heavy cabling), fuses, relays, the ignition switch and terminations. Basically, with the key held in the "start" position, the starter is either getting power or it isn’t. With the key in the "start" position, if the starter motor is getting power but it doesn’t work, the starter is condemned and replaced. On the other hand, with the key in the "start" position, if there is no power to the starter, then the circuit is traced until the fault in the circuit is found. In addition to a faulty ignition switch, faults can include high resistances, due to corrosion, wire strand breaks, or loose terminals, which can only be diagnosed using a voltage drop test. If you desire that a certified mechanic resolve this, please simply request a no start diagnostic and the responding certified mechanic will get the problem diagnosed and repaired for you. Please let us know if you have further concerns or questions as we are always here to help you.
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