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Discussion Starter #1
Car details: 2003 Focus ZTS 4DR with the 2.0 Zetec and MTX75 trans. High miles (200k+).

Before I get started, I have searched very thoroughly, and performed several of the common procedures to fixing this problem, all to no avail. I know this is a common problem, but my circumstances seem to be a bit unique sadly. [dunno]

So, in a nutshell, I'm having the dreaded intermittent battery light that I am learning is very common for these cars.

It all started about three weeks ago on the way home during a storm. Battery light came on and went off so quickly a barely noticed it. Considering the weather, I figured I had hit a puddle and caused the belt to slip for a second. No biggy.

Since then, it has started coming on more frequently and during dry conditions, letting me know that something is, in fact, wrong. Most recently it came on and stayed on for a solid minute. I'm definitely concerned at this point.

The light seems to come on whenever it wants to. I've had it happen when it's wet, when it's try, coming to a stop, going around a curve, driving at low RPM/low speed, driving at 70+mph and 3000+rpm on the interstate.

Here is what I have done to try to fix it:

*Cleaned battery terminals thoroughly.
*Checked alternator pigtail from alternator plug back to main harness on firewall. Nothing out of the ordinary.
*Tensioner and belt have less than 10k miles on them. Checked both, and they work great.
*Replaced alternator with rebuilt unit from Advanced.
*Checked battery with voltmeter. 12.82V across the terminals. When car is running at idle, it is around 14.4-14.8 with all accessories running.
*Hooked voltmeter up to battery while wiggling wiring harness trying to check for shorts/cause light to come on. No luck.

At this point, I'm kind of stuck. I'm going to put the OEM alternator back on there and get my $211 back, but I don't really know where to go. I don't think the battery is bad. It is a few years old, but it is a Motorcraft unit and has never failed to start the car, even when it got into the negative temps several times.

Unless I have terrible luck, the alternator can be ruled out as a possibility. This points to wiring, which is the least fun to troubleshoot. Should I strip the pigtail back further into the harness on the firewall to check? It honestly felt very solid. How about the main (larger) alternator wires? I found part number YS4Z-14301-JB that seems to correspond to them. Might be worth a shot.

I'm very dependent on this car for transportation right now. I really would like to get this thing back to reliable as quickly as I can.

Thank you all for the help! :)
 

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If you have a belt right at end of range then tensioner and belt could appear to be perfect yet belt ever so slightly bottoming tensioner on end stop would do that. Belt then occasionally slipping a little bit.
 

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...
*Replaced alternator with rebuilt unit from Advanced.
...
I'm going to put the OEM alternator back on there and get my $211 back...

Unless I have terrible luck, the alternator can be ruled out as a possibility.
It would not be "terrible luck". Rebuilt Alts from car part stores often fail.

Since you have another Alt, do as you say, replace the Alt... And don't worry about the other possibilities, or additional troubleshooting, until after you replace the Alt. When you return it, ask the part store to test that Alt on a test bench-> before you ask for your money back.

The original OEM Alt was OK before you replaced it right? Or was it also giving you this or other problems?
 

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Discussion Starter #4
If you have a belt right at end of range then tensioner and belt could appear to be perfect yet belt ever so slightly bottoming tensioner on end stop would do that. Belt then occasionally slipping a little bit.
It was the same size as the OEM belt, if I remember right. And I have been running it for close to 10,000 miles before this started. Is it still a possibility?

It would not be "terrible luck". Rebuilt Alts from car part stores often fail.

Since you have another Alt, do as you say, replace the Alt... And don't worry about the other possibilities, or additional troubleshooting, until after you replace the Alt. When you return it, ask the part store to test that Alt on a test bench-> before you ask for your money back.

The original OEM Alt was OK before you replaced it right? Or was it also giving you this or other problems?
The original alt was what this problem started with. I went and purchased a rebuilt unit hoping that the original one was on the way out. However, the problem still persists with the replacement alternator. :( I installed the replacement alt last night, drove 125 miles this morning without issue, then the light came on randomly.
 

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I would be tempted to Load Test or replace the battery. I would also double check the Battery grounds on the car frame/chassis. And maybe the ground cable from engine ->to-> car frame too.
 

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Discussion Starter #6
I would be tempted to Load Test or replace the battery. I would also double check the Battery grounds on the car frame/chassis. And maybe the ground cable from engine ->to-> car frame too.
Please forgive the stupid question, but where could I take the car to load test the battery? I have a small battery charger at home that has an alternator test features, and I believe a battery test feature that I have already tried.

Also, what are the locations for the chassis grounds on this car? I checked while I was under there, but nothing was obvious.

Thanks again!
 

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Most car part stores offer free battery testing. Bring the battery to them.

Battery ground cable = follow the neg black cable from the battery to the drivers side wheel well; it connects to the frame right there. Disconnect it from the frame, clean it good, "wire-brush shiny metal good".
 

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It is possible that the "new" rebuilt alternator is defective. Ford uses the Smart Charge circuitry in the Focus. In a rebuilt alt you may well have a bad Smart Charge circuit and it will turn on the battery light periodically. I don't think that the parts store can even test for a bad SC circuit in an alternator (somebody correct me here if they can do that now). I think all they check for is bad diodes and does it produce power...if so, they call it good.

If everything else gets ruled out, then I would exchange the alternator.

As for the possible belt slippage mentioned, are you sure the tensioner is good. A new belt on a bad tensioner will slip. The tensioner must move freely...old ones tend to bind...you can feel it if you move it from one end of its rotation to the other with your wrench.
 

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Discussion Starter #9
Most car part stores offer free battery testing. Bring the battery to them.

Battery ground cable = follow the neg black cable from the battery to the drivers side wheel well; it connects to the frame right there. Disconnect it from the frame, clean it good, "wire-brush shiny metal good".
Thank you for the tip! I'll pull the wheel and clean the ground off really good.

It is possible that the "new" rebuilt alternator is defective. Ford uses the Smart Charge circuitry in the Focus. In a rebuilt alt you may well have a bad Smart Charge circuit and it will turn on the battery light periodically. I don't think that the parts store can even test for a bad SC circuit in an alternator (somebody correct me here if they can do that now). I think all they check for is bad diodes and does it produce power...if so, they call it good.

If everything else gets ruled out, then I would exchange the alternator.

As for the possible belt slippage mentioned, are you sure the tensioner is good. A new belt on a bad tensioner will slip. The tensioner must move freely...old ones tend to bind...you can feel it if you move it from one end of its rotation to the other with your wrench.
That would definitely be my luck. What is the function of Smart Charge, exactly? I am familiar with how an alternator works, but this is the first I have heard of this. I'm going to start tearing into wiring harnesses, for now, I guess.

The tensioner and the belt were replaced at the same time. Old tensioner seized, causing the stereotypical squeaking at start up that these cars like to get.
 

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Thank you for the tip! I'll pull the wheel and clean the ground off really good.
No need to pull the wheel off. The connection is inside the engine bay & is very close to the battery.
 

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What is the function of Smart Charge, exactly? I am familiar with how an alternator works, but this is the first I have heard of this.
The Ford alternator uses the PCM to calculate the best charging senario based on more than just the battery voltage. The circuit inside the alternator must be good for this to work. Here is a brief description: http://www.napaechlin.com/Ford-PCM+Controlled+Charging+System/Content.aspx

FYI: European Fords use a Smart Charge setup that requires a silver calcium battery, but ours uses a standard lead acid type. So, if you Google "smart charge" don't be thrown off by that.
 

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The alt testers DO check the duty cycle on PWM alts by ramping it up and down but only for a few seconds. Obviously a longer period could show up like a bad regulator that gets hot then PWM starts cutting out.

If you want to know if belt length is in relation to the tensioner, then you have to look at tensioner for the range indicated on it, or even scribe one if the tensioner cheap enough part it does not have it, then determine if the belt is in the proper range. It needs to be in the middle of the tensioner range to not be too loose or tight. And yes, 10K miles could let a belt slightly too long then begin to stretch enough to then be loose later. I've seen identical marked belt length belts vary by a half inch depending on maker, or enough to not work with tensioner, just went through that a while back myself. New tensioner then had belt too short, it had been running on the car for years before. The tensioners can slightly clock different from each other, or, the range does not natch exactly across the full swing of the part. I.e., one swings from 9-12 o'clock, the next one from 10-1 o'clock. Little differences that can kill you.
 

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The alt testers DO check the duty cycle on PWM alts by ramping it up and down but only for a few seconds.
That's good to know. I was just talking with a mechanic friend about this a couple of weeks ago and he wasn't sure if they checked it or not. He said he had found alternators that appeared to be working (they put out voltage), but they still threw a battery light.
 

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Discussion Starter #14
The alt testers DO check the duty cycle on PWM alts by ramping it up and down but only for a few seconds. Obviously a longer period could show up like a bad regulator that gets hot then PWM starts cutting out.

If you want to know if belt length is in relation to the tensioner, then you have to look at tensioner for the range indicated on it, or even scribe one if the tensioner cheap enough part it does not have it, then determine if the belt is in the proper range. It needs to be in the middle of the tensioner range to not be too loose or tight. And yes, 10K miles could let a belt slightly too long then begin to stretch enough to then be loose later. I've seen identical marked belt length belts vary by a half inch depending on maker, or enough to not work with tensioner, just went through that a while back myself. New tensioner then had belt too short, it had been running on the car for years before. The tensioners can slightly clock different from each other, or, the range does not natch exactly across the full swing of the part. I.e., one swings from 9-12 o'clock, the next one from 10-1 o'clock. Little differences that can kill you.
Very interesting! I'll check the tensioner's travel range when I head out this afternoon. Now that you mention it, I did see a small amount of belt dust below the alternator pulley when I was changing the alts out. I just assumed it was from the old belt slipping on start up and didn't sweat it.

If the belt was slipping, especially enough to make the battery light come on for 30+ seconds, wouldn't it make a god-awful squealing noise, though?

If it isn't the belt, when I get home this weekend (I guess I should say IF I make it home this weekend [paranoid]), I will go ahead and check the wires going to the starter and junction box for corrosion or breaks, along with checking the grounds mentioned earlier in this thread. Then get the battery load tested at AutoZone or somewhere similar just in case it is somehow killing these alts.

And, if all else fails, what is the best course of action for the alternator? I looked for a new Motorcraft replacement, and all I could find were remans, which is what this new alt appears to be. Just keep taking these things back until I get a good one, or what? Any brands that I should try to look for in the future?
 

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I wouldn't rule out the alternator, my first go around with my alternator took 3 alternators from the part store before I got a good one. Each time they would work with no problems for a day or 2 or however long it took me to go 100-200 miles and then the light was back on. Start the car and check voltage at the battery it should be between 13.5-14.5 or close to that with the light off, then let it run until the battery light comes on and check voltage again and check it a few times a minute or so apart and see if you lose charging voltage while the light is on. If it's like mine you should read less than 12.6 at some point while the light is on, I would try another alternator from the part store before I cut into the wiring, and if you feel confident enough you can buy a new rectifier bridge and voltage regulator with the brushes for about 80 bucks online and reman your old one yourself.

Also I would simply do a continuity test/resistance test and a voltage drop test on the alternator wires instead of looking for a visual problem, you more than likely won't see anything with just your eyes you will need to read the meter to be sure
 

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I wouldn't rule out the alternator, my first go around with my alternator took 3 alternators from the part store before I got a good one. Each time they would work with no problems for a day or 2 or however long it took me to go 100-200 miles and then the light was back on. Start the car and check voltage at the battery it should be between 13.5-14.5 or close to that with the light off, then let it run until the battery light comes on and check voltage again and check it a few times a minute or so apart and see if you lose charging voltage while the light is on. If it's like mine you should read less than 12.6 at some point while the light is on, I would try another alternator from the part store before I cut into the wiring, and if you feel confident enough you can buy a new rectifier bridge and voltage regulator with the brushes for about 80 bucks online and reman your old one yourself.

Also I would simply do a continuity test/resistance test and a voltage drop test on the alternator wires instead of looking for a visual problem, you more than likely won't see anything with just your eyes you will need to read the meter to be sure
With the lights off, the voltmeter read about 14.86V whilst the car was running with no accessories. With everything running on high, the voltmeter read about 14.4 at idle.

What makes this tricky is I can't predict when the light is going to come on. I let the car idle with everything running for almost half and hour this weekend waiting for the light to come on, and it never did. Sometimes it will come on within minutes of me leaving the house, other times I will be 50+ miles into a trip before it rears it head.

What I CAN do is put the odometer into diagnostic mode, and then check the voltage there while driving it home. Odds are, the battery light will come on then. Will that show me the info I need?

What is considered an acceptable range for the resistances in the wires? I would assume that a short would probably just show up as infinite. Which wire runs should I measure, also? If I remember right, it goes Alt->starter->junction box. Correct?

And finally, are there any guides to rebuilding one of our alts online? I'm decently mechanically savvy, and have "some" experience with electronics so I may be up to the job if I have instructions to go off of.

Thank you again!
 

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That should work, you can put it in engineering mode and watch your voltage while you drive, I'm sure you will notice that the charging voltage drops off when the light comes on. I had the same problem testing mine, you just don't know when the battery light will actually come on, if you keep driving it and let it get worse it will start to come on faster and more frequently making it easier to test, but you run the risk of getting stuck.

As for acceptable rresistance it should be next to nothing, I n the milliohm range. Mainly your looking for am open circuit or high resistance. You can do a voltage drop test as well to confirm a wire is bad if you suspect it, as for the exact wires to check I'm not sure off the top of my head I'd have to look at a diagram. The main charging wire though should come off the battery to the starter and then to the alternator, that will be your main charging wire but I doubt you have problems there, or anywhere in the wiring.

I haven't seen a guide on how to rebuild our focus alternators, I've just been taught how to do it through school, we had to take apart and rebuild many alternators and starters to show we knew how to diagnose a problem and point out EXACTLY what it was, not just the broad "the alternator is bad". They wanted you to point out that it is the rectifier bridge, or the voltage regulator, or the brushes, etc. Point being they wanted us to be VERY specific. It is pretty simple to reman our alternators and I'd be willing to help you do it if you want. I would do a write up on it if I had a spare alternator to take apart and rebuild, but mine is still good haha.
 

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What I CAN do is put the odometer into diagnostic mode, and then check the voltage there while driving it home. Odds are, the battery light will come on then. Will that show me the info I need?
My guess is No, at least in your situation. You may or may not see a voltage drop while driving. The Bat Light can come on with or without a low voltage condition.


What is considered an acceptable range for the resistances in the wires? I would assume that a short would probably just show up as infinite. Which wire runs should I measure, also? If I remember right, it goes Alt->starter->junction box. Correct?
"infinite" resistance shows up when detecting an Open, not a short.

It goes; Alt->starter->Bat
Then it goes; Bat->Junction box

And finally, are there any guides to rebuilding one of our alts online? I'm decently mechanically savvy, and have "some" experience with electronics so I may be up to the job if I have instructions to go off of.
If you still have your OEM Alt off the car, yes! great idea to rebuild it yourself. Replacing the VR and Rectifier is something I want to do on mine in the near future. Mine is original and will need rebuild or replacement soon.

If interested, watch these 2 videos.
https://www.youtube.com/watch?v=BkL5BdFLsMg

At 3:55 in this video, note how he uses a feeler gauge, in order to prevent the brushes from hanging-up during removal of the VR.
https://www.youtube.com/watch?v=JuKCrnoe_Vs
 

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Use a bent straight piece of paper clip to hold brushes up either removing or installing. Holes in brushes and the regulator case for it.

Biggest problem on these is the rear bearing 'tolerance ring', or the sleeve that sizes bearing to the case. They destroy when removed. If you get one and remove the raised edge that locks to tear it up they then come off over and over, at least until old enough the plastic DNFs. Problem being there though, once they slide on/off, nothing to hold them in place. I use like a freeze plug or the plastic OEM snap on cover to hold it in place, that then being held by a tab bolted down using the unused 8 mm. bolt hole on back case.

Oh ho, second link even has him removing that edge on the tolerance ring. I remove the three notches as well. Part then comes in and out fairly easily.

First link is abysmal, the guy tears down way too much, you never tear down the front at all unless changing the front bearing. Most repairs involve the back only like second vid. And whatever you do do NOT follow the advice in first vid that you really don't need to solder the diode plate to field connections. Good way to have a working alt that quits working 6 months later. I don't cut short the field leads either, butchery if you are planning on soldering anyway, you preserve as much length there as you can at all times. Unsolder the old, not cut short.
 

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Discussion Starter #20
Guys,

thank you for all the great info yet again! I will look into those links about rebuilding my own alt if it looks like that is going to be my problem.

I don't have any updates as of yet. When I get off work today, I will make the 150mile trek back to my garage and spend all weekend poking around with a voltmeter seeing what I can find. On the trip, I'll keep the cluster in engineering mode to see if I notice any voltage drops.

One things I did notice earlier today, was that when the cluster is reading volts, and the key is OFF, the reading is about 11.8-12.0. Is that considered normal, or could that potentially point to an internal issue with the battery? Car is still starting like a champ, even in the 40* weather we are having.

I'll post back with more details later!
 
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