What's up with the alternator



Car run great all day. At night came back from work and parked temporary some distance from my spot. Run upstairs to drop some stuff and came back to repark the car by reversing it into my spot about 40-50 ft. Engine started fine. On start, the radio, heater were on and since it was a short distance I did not turn my lights on. I backed into my spot but wasn’t satisfied with the angle. Moved forward, put it back in reverse and at this point I turned on the lights while I was moving in reverse. The engine had an electric shutdown and stopped. It was electrical because the radio reset. I immediately cranked the engine and started fine. I moved into my spot, stopped the engine and waited a minute or two. Restarted the engine and again no problem. Drove around for 10-15 minutes with no problems. So I am concluding that the battery was fully charged all the time. If it wasn’t the car wouldn’t have started the first time. The battery is less than a year old and if it was charged then the alternator must be at least charging the battery fine. Since the car was moving when the shut down occurred it must be the alternator. But what is it? An internal short? Regulator? And can it be diagnosed beyond of what just happened? And can I have a bad alternator and still have a healthy engine start? No warning light (dimming or flickering). Technician at the dealer had diagnosed an overcharging alternator 1 year ago. Since then I discovered that the battery was the wrong kind and dismissed that diagnosis after replacing the battery and constantly checking for overcharging. And if it is a bad alternator and needs replacement that’s fine, but I am concerned that maybe the engine belt that drives the alternator is somehow malfunctioning. Is that even possible?


It is not likely to be the alternator. Normally the car can run for a reasonable distance on battery only. Even if the alternator died, the car would continue for run for a while. I would suggest a relay, bad battery cable, bad ignition switch etc.


It’s not the alternator. There is a bad wiring connection somewhere. You, I mean, a qualified mechanic, could start testing with a volt/amp meter and do the electrical checks with the meter while wriggling the wiring.


after reading your post 4 times i figured you need to re look at what IS working.

the engine starts. the lights come on. the battery HAS power. the Battery IS getting charged (or it would be dead by now).

since the battery IS getting charged, the problem is not the alternator. you mention that the battery was changed. you mention the wrong battery was installed. what is the other battery? usually a battery that is not an exact replacement is acceptable. (more info on this is needed)

you mention the radio was “reset” i take that to mean it lost the preprogrammed memory? if that is the case, then you had an electrical wire, cable or fuse issue.

the serpentine belt is a red herring. do you have power steering? if you do, and it’s working, then you have a belt that works. taken into context with the fact that you battery is NOT dead, then the alternator is working.

since you had a diagnosis of an “overcharging alternator” a year ago. why would an alternator “overcharge” aside from the obvious (a bad voltage regulator?) it will overcharge when it thinks the battery is low. one way that the battery would look “low” is if the cables, connections or fuses have corrosion or frayed wires, or broken wires and not enough voltage was getting through to the regulator. do i take it that you DIDN"T replace the alternator? while that may not be necessary, it sounds like you did nothing then to figure out what was wrong with it either.


No offense, but your “logic” (“wrong” battery was installed, therefore alternator diagnosis was wrong; since the car was moving when it shut down, therefore it must be the alternator) indicates a lack of basic knowledge of how the electrical system works. You’ll need someone well versed in this area to track down the apparent intermittent open circuit.

You don’t mention what type of car this is. If it is a GM, a common problem is the positive battery connector. Corrosion builds up, unseen, under the protective boot, between the two ring terminals. All sorts of weird problems may ensue.


This is by far one of the most CRYPTIC posts I’ve ever read. Took me 3 times to actually figure out what the problem was.

It is NOT the Alternator…It sounds like a switch (ignition switch is a good bet) or a some relay. If the alternator is bad the battery will start loosing power slowly and you’ll notice things like heater fan slowing down or lights dimming or radio not working…Then you’ll eventually loose power…but you’ll know it before that happens.


OP: I agree. The only problem with the alternator is that is consistently giving me 14.6 Volts of charge back to the battery. So it is slightly overcharging by 0.1 V which should not be a problem


OP: Could be a bad wiring connection, sure. If there is then it is something that does not drain the battery. It almost feels like someone reached inside the engine those moments and cut the cable between the alternator and the battery. But as the previous person mentioned the car would have run for a while.


more info on that battery -> the other battery was smaller and it was loose inside the battery compartment. But since there have been almost a year I don’t remember the exact spec differences between the ford battery I have now and the other one.

radio was “reset” -> yes it lost the preprogrammed memory when the car died. All electrical system had a shutdown. Radio came back with no programs, typical when disconnecting the battery from the car.

power steering -> yes. Power steering is working, with the exception that the fluid is darkened and never been changed. But no power steering performance issues.

The cable that runs from the battery to the alternator was replaced a year ago and it looks in pristine condition throughout the length. Even if the alternator still overcharges the battery (see my reply above) - which it does if you believe those numbers by 0.1 V above the normal range, it would still not explain what happened. No I didn’t replace the alternator, because after I changed the cables and put a new battery the car run with no problems until last night. I wouldn’t replace the alternator unless I have evidence to support that it is doing something wrong.

Car -> Ford Focus, 2002 2.0 SE DOHC, automatic with 136,000 miles on.


Car -> Ford Focus, 2002 2.0 SE DOHC, automatic with 136,000 miles on

A year ago, it did the same thing. But then I was able to trace the problem in corrosion on the cable
close to the battery terminal that was creating a short. The corrosion was caused by battery acid that was spilling out of the battery. The mechanic at the dealer told me it was the wrong battery which was balking and boiling. To correctly diagnose a problem with an alternator (correct me if I am wrong) one needs to make sure that the battery is ok first. When I got the diagnosis for the faulty alternator, the battery was assumed it was working ok.

As for my lack of knowledge on the electrical systems I am the first to admit that. At least I know that.


I don’t usually do “me too” posts, but everything NYBo says is correct. Your alternator is not the problem. Your logic that arrives at that conclusion makes no sense. The problem is almost certainly a loose or corroded connection, or bad relay, or bad switch. I’m guessing switch.

Don’t take this the wrong way. I’m not trying to insult you, just trying to get you off a false trail.


OP: Sorry. I posted the message at 1 AM west coast time and I was indeed not just cryptic but incoherent as well. I checked the relays (visually) the look ok. None of the typical symptoms of a failing alternator are present. The car has never had issues of cranking successfully.


I am convinced the alternator is not the problem. I would be ecstatic if it was. Then you pay $200 and put a refurbished one on and be done with it. Issues with the wiring is a problem because you end up paying a lot of labor. It’s been 12-14 hours since what happened and the car is purring like a cat. I took it to a neighborhood mechanic this morning who just dismissed the problem on the grounds that he can not duplicate the problem. Now i have an appointment at the dealer tomorrow that is going to cost me an arm and a leg.

And don’t worry. I don’t get insulted about stuff that I don’t know.


The only problem with the old battery was that it was apparently not the OE size and wasn’t properly secured. But electrically, that wouldn’t matter (unless was physically damaged from bouncing around, a definite possibilty after a while), and wouldn’t cause overcharging. The mechanic was blowing smoke.

Yes, the battery must be in good shape to test the charging system.

While the alternator might be overcharging, that didn’t cause the problem you had. There is an intermittent open circuit somewhere. This may be maddening to find.


yes, i know. I am at work all day but my wife is driving that car with my 3 year old from place to place and I just freaking worry about it because there is not predictability.


Just give us the story of what is happening today, not a year ago. The flash-backs are confusing.
The only symptom, right now, seems to be: there is an intermittent loss of electrical power, either total or partial. Let’s consider that problem, before considering other theoretical things.
The alternator charge voltage, unloaded, is NOT a problem.
You CANNOT look at a relay and determine if it is good, or bad.
All of the power, and ground connections, need to be checked, preferably with a volt/ohm meter. “Looking at”, is inadequate.


And can I have a bad alternator and still have a healthy engine start?

If the battery is fully charged, but the altenator is bad, yes, you can have good strong engine cranking.

And if it is a bad alternator and needs replacement that’s fine, but I am concerned that maybe the engine belt that drives the alternator is somehow malfunctioning. Is that even possible?

It would only be possible if the belt has stretched past the point that the tensioner no longer keeps the belt tight on the various pulleys. If that was occurring, you would hear squealing when you are accelerating.

From your description of the events that took place, to me is sounds like there is a loose connection somewhere between the battery and the vehicle.

Check the positive and negative cables on the battery, and make sure they are tight.
Trace the cables to where they connect to the car, and make sure they are also tight.
Check for corrosion at those various connection points.



Well, I think you are jumping the gun on taking it to the dealer. As far as I can tell from your story this problem has only occurred once, last night when you were moving the car. Are you sure you didn’t bump the ignition switch when you were changing gears or turning around to see where you were going? I understand your are worried about the car leaving your wife and child stranded somewhere, but since it restarted OK last night it probably will again, at least for a while, if the problem ever comes back. This sort of thing generally gets worse slowly, and the dealer and mechanic won’t be able to figure anything out until it happens often enough for them to see it happen.


OP: I give you the flashbacks because i think it is the same problem that was never quite addressed. You’re right about the relays they can be bad even they look good. As I mentioned I am taking it in tomorrow to have it checked out. But the purpose of my story here was to collect intuitive based possibilities so I can mention them tomorrow.


would bumping my ignition switch make the radio lose it’s presets?