The car won't start unless you jump it it runs fine when running but as soon as I turn it off it won't start I change the battery and alternator the wires are good I have checked out all is the some kind of sensor that would keep my car from charging it also started to drop into neutral wilt driving I shift down and back up and it works fine for about twenty miles then I have to shift manually again
My car has 198354 miles.
My car has an automatic transmission.
During the most recent episode when the car yet again failed to start, the diagnostic would begin with testing of the battery. If you have a fully functioning charging system (you mention the alternator is new but charging system should still be tested) and the battery is new, and was fully charged when you last left the car, but the battery turns out to be now be "discharged", in that scenario you have a parasitic (excess) load on the car’s electrical circuits that is causing the battery to discharge even when the car is off. If there is excess current flow that is slowly draining the battery, a Mechanic would use an ammeter to test all of the various circuits until the faulty circuit with the excess load (current draw) is found. Then that circuit is traced to find the fault and repair it. That requires an electrical diagnostic.
A second possibility would be considered if the battery tests fine (fully charged, not discharged as in above scenario) and yet there is no starter motor operation. In that scenario, that is if there is no starter operation with the key held in the "start" position, the procedure is to test for power to the starter motor. If there is no power, then 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 a fully charged battery, and 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 the starter doesn’t work, then 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. Requesting any of the above services I have referred you to will get you to the same end point: we will get the fault diagnosed and repaired. Please let us know if you have further concerns or questions as we are always here to help you.
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