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WEIRD Battery light on, but no problems...?

83K views 37 replies 19 participants last post by  amc49 
#1 ·
My battery light came on, and has been on, all day today while I have been driving. I know this usually means bad alternator, weak bateery, or loose wires somewhere.

So I bring out the DMM and do some testing. After I first noticed the battery light come on, I have to drive about 5 miles to home. Figure the battery (Optima Red Top, about 8 months old) would show a decent amount of voltage loss if the alternator was bad. Put the DMM on it, and about 13v..... weird.

Start the car up, test the voltage on the battery again..... 14.5v.... double weird. The alternator is running fine, putting out full power. I turned on the radio, headlights, AC, etc, and hardly ANY voltage drop at all.

Check all wires, power ground, etc, and everything is fine. I have now driven for about 60 minutes or so with the battery light on. When I turn the car off, battery still reads about 13v.

So WHY THE HECK IS THE BATTERY LIGHT ON?

also, I have turned the car off and restarted multiple times, and the light is on everytime. The car has no problem whatsoever turning over, starts like usual. I'm starting to think there might be a problem with the bulb for the battery light!
 
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#2 ·
Maybe the voltage regulator went out on the alternator. Sending that light on for a MAX voltag. Just a long shot, because a stock alternator or even High output wont put out 14.5. Thats pretty damn high.. I HAVE a High output, and I MIGHT get that 14.5v. Especially if there is no voltage drop when you turn the AC and or lights on. just my .02 worth a shot, see if you can pull a code, stating too high a voltage or something of the sort.
 
#4 ·
Ok, Well I DO have a High output also. What i was trying to get at, is maybe the voltage regulator is going or IS bad, causing a high voltage issue, which in turn might turn that light on. That is just a guess, if there is no other issues. How long has the altnernator been in the car?
 
#6 ·
UPDATE

Today the car started doing something weird again. The battery light has been on since I posted about it, but now a new problem. SOMETIMES, not every time, when I come to a complete stop and put it in first gear, the car just dies. It doesn't shake like when you take your foot off the clutch w/o giving it gas, it just gently dies. Any ideas?
 
#7 ·
I have heard of that problem before. I thought there was a TSB on it. Something about stalling during operation. My friend has an ATX 01 wagon which dies sometimes too. It only has been happening when it's hot/humid out like it has been lately. I think a reflash fixes it, but I can't remember the reason, might wanna PM WD40 and ask him about it.
 
#8 ·
took it to Advanced. No codes were being put out. Check battery and alternator, everything was fine. Belts were all fine. He saidthe only thing he could think of would be a glitch with the attery light itself. I'm still taking it to the shop tomorrow.

Oh, and it hasn't stalled since earlier. Humidity has gone down, wonder if that is what caused it?
 
#9 ·
My 02 svt has been having the same problems. Whenever i get into the high rpms on the highway the battery light comes on. Last night i got onto the highway, there was a electrical burn smell coming from my vents. The battery light came on and stayed on for 5 minutes. Then it went off. Everything
checks out fine but im going to replace it just in case.
 
#31 ·
I have a 2002 focus, 230,000 miles and for the past three years the charge light comes on a few seconds after starting. Everything checks out good, new alternator, decent output, someone mentioned that ford used a special battery, whatever, I think of it as a pretty bit of decoration and I have never had a problem with flat or overcharged(hot) battery.
 
#11 ·
Just to put the record straight- a 'High Output Alternator' does NOT output more volts. It WILL output more current, but the voltage is always between 13.8 to 14.4 volts.

You might want to check the pigtail wiring on the back of the alternator. This is a known weak point on the Focus and could cause your problem.
 
#37 ·
i just put a used enine in my 06 zx4ses and have a few problems. THE BATTERY LIGHT never came on before i changed the engine. I noticed the connetor two wires back alternator near the exaust manifold pretty sure its a bad connection i havent messed with it because its usually hot or im busy car runs fine. I tried to hole the harness up tighter to something on top the engine ribght there and it seems to go away then comes back on. PRETTY sure its that connection if i read farther and that fixed it im a genious.

I have abs brake and air bag lights on and im trying to figure out what the white two wire electric sensor behind the bumper cover and licene plate bracket exacty is. NOT wsure yet but i thinik it a impact sensor and i removed the bumper cover and kinda tossed it around till i got the engine back in. Bet yall that sensors messed fop from the bumper cover sitting on the back driveway in the rain.. Anybody know what im talking about i thinik it was white with two spade connectos one on each side. IT IS NOT up near the hood latch. IT was a bitch to get the wires on it puyttingh the bumper cover back on. Anyone know what that is i cant find it wanna say it was 2-1/2 inhes long one inch tall about 3/8 deep tith two wires one on each side way up under there. I had a few extra connectors down there when i got done too. Cars doing fantastic thought.
 
#14 ·
#15 ·
On more than just on forum, I got the distinct impression that the Ford Focus had some sort of mystery surrounding my Battery light symptom. At least four instances were cited where the post indicated both battery and alternator replacement did not resolve their battery light issues. $120 for a battery, $600-800 I read were typical costs for alternator replacements, all to no avail. From this, I concluded that there was some other potential cause for my problem.

I ended up buying a new battery, based on the results of a test by a local shop. Not the answer. I decided to put the old battery back in and drive the car till something fell out of it. Then, I would be certain of the defective component.

My alternator toasted on Saturday night. As I might expect, once the alt finally gave up the ghost, the appropriate computer shut off all non-essential electricals, providing all available power to the engine (and, I supposed fuel pump) until the battery was too exhausted. It got me as far as I needed to go.

In NJ, one of the few service agents open on Sunday was Pep Boys. They secured an alternator from NAPA and installed it in a couple hours for $472. No mystery, no rocket science.

Seems like my ST and I are back in Focus.

Now, onto the reverse light switch.

(The hidden message here-don't overcomplicate this. The way my alternator failed-lots of strange electrical issues. The grand finale-all electricals shut down until the battery was dead.)

I'd replace the alternator. If you're not confident doing it yourself-I wouldn't hesitate to take it to Pep Boys (as silly as that sounds). From what I've read-they gave me a solid price.
 
#17 ·
Now, onto the reverse light switch.

I'd replace the alternator. If you're not confident doing it yourself-I wouldn't hesitate to take it to Pep Boys (as silly as that sounds). From what I've read-they gave me a solid price.

I have a contributed to a thread on this, its quite simple and likely the switch.

I had identical symptoms to your alternator, when a load was applied it would drop just below 13v. I changed the alternator myself, it took 2h out and about 30min back in. doing it again, i could probably have it out in about 30. it is a bit of work but only nut and bolt work. Its a good excuse to change the belt and i replaced the tension idler at the same time as the bearing was trashed.
 
#16 ·
"The hidden message here-don't overcomplicate this"
Hindsight is a wonderful thing. With all problems it is difficult to arrive at the final solution without going through all the possibilities based on the information to hand. In my experience, the only time a battery light has come on was when the alternator failed. You had a fairly recent alternator but it was proven to be faulty. We could have said- change the alternator- and the problem could have been the wiring. Glad you have solved your problem though.
 
#18 ·
I had this problem. I could not figure it out. My alternator went bad so I replaced it. After replacing the alternator the battery light came on (was not on before). I then replaced the belt and checked voltage under all different loads with lights and a/c on. Everything worked perfect. Even had autozone test it. I decided to pull the bulb out of the dash. That was my simple solution to worrying about it anymore.
 
#19 ·
The battery light in my car came on while driving. After I turned the car off I noticed that the battery light came on each time about 15 seconds after starting the engine. I checked the charging voltage and amperage with a digital mulitimeter- charging system was working but rather weak. The next day I fully charged the battery and took the car out for a drive...the battery light was on the entire time and the car completely died with a dead battery about 30-40 minutes after driving. All this while my multimeter was showing alternator output (however low and weak).

I decided to upgrade and ordered a new Bosch hi-output replacement (220 amp) for $249.00 shipped from an eBay seller since I live in a hot climate, run the air conditioner, and also tend to run a power inverter and other electrical accessories inside the car. I installed the alternator myself- took me about 3hrs.

Battery light no longer comes on. Charging voltage is a solid 14.2-14.4 volts off-idle. I didn't check the charging amperage because it would probably fry my multimeter.

But now I have a new "problem". This new Bosch hi-output alternator seems to have to spin at a higher RPM before it kicks in and actually charges. My car idles at about 700RPM and I am getting less than 12.5v at the battery. If I increase engine RPM to 900 then charging voltage immediately jumps to a solid 14.2-14.4v. The Bosch alt has the same diameter pulley as the OEM alt I removed, so alternator shaft speed is exactly the same.

I mostly drive my car in the lower RPM ranges and also do a lot of relatively shorter distances in city (ie. stop and go driving), so this poses a problem - my battery now is usually discharging considering the way I drive, unless I hit the open road or something (which I don't do too often).

I never had this low rpm charging issue with the stock alternator :(
 
#20 ·
Posted via FF MobileSeems like the current problem is a lower than normal Idle RPM. Mine Idles at about 900 when warm, and readjusts to that when A/C is engaged (pops higher then settles down) so that seems like the normal speed for idle. If the IAC seems to be responding normally you may have a vacuum leak or other cause for low idle.... Others may know your normal idle, I can`t see your model info on Mobile, just guessing that all models have similar std. Idle RPM....
 
#21 ·
I have a wagon with the Zetec engine. I got this car brand new and the idle speed as always been around 700rpm from day one (after warm-up). Of course the idle from a cold start is a little higher (somewhere around 1000-1100). I'm assuming the idle air control is working correctly- with the air conditioner on the idle speed doesn't increase but pretty much stays constant around 700rpm (even if the electric fans are on out front).

Like I said, the car has always worked like this. I never had any low charging output issues at idle with the OEM alternator.

The missus has the same car as I do (SE wagon), only one year older, less factory options, and with quite higher mileage. Same Zetec engine however. Her's idles at around 700rpm after warm up also. I checked charging voltage on her car at idle yesterday (no lights or other electrical stuff on) and it produces a good 14.0-14.2v, at idle. Then I turned on everything I could possibly turn on- lights, heater blower, front and rear windshield wipers, rear defogger, interior vanity lights, radio, and the car still produced well over 13.2v at idle- still more than enough to charge the battery.

So I am left to conclude that the Bosch H.O. I put in my car won't really work unless I am driving at least 1000rpm, which is definitely on again, off again in city driving (NOT good for the battery). And with the amount of electrical load I put on my car, this is a problem :(
 
#22 ·
One more thing...

I'm wondering if there are any unseen issues with the battery itself? I installed this battery new less than 12 months ago and to this day I have never had any issues with the battery itself, but due to the recent alternator failure I had this caused the battery to go completely dead on about 3-5 occasions.

I know this can be detrimental to any lead acid battery. The hot climate I live in probably makes matters worse. The battery still starts the car fine and accepts a slow charge from my WalMart charger. After charging it reads a good 12.68-12.8v although this could possibly just be a 'surface charge' reading???

Any ideas whether I should replace the battery? It was just a low cost replacement to begin with but I'd rather not buy another battery right now if I can help it.

One thing I remember is that my alternator failed a few years ago at around 40k miles while the car was still under factory warranty. Rather than fiddle with it myself I took the car to the dealer (considering that the warranty was still in effect). Before taking it to them I verified little or no charging output myself. They replaced the alternator- and ALSO the battery. Prior to that I never had any issues directly related to the battery but they replaced it anyway- I was only expecting them to replace the alt. This has me wondering if my present battery has some unseen fault and should be replaced.
 
#23 ·
Posted via FF MobileProb should have run mine longer for a fully warm reference, but it ran recently so not really "cold". 6-700 isn`t unusual as a low idle speed, just didn`t know your "normal" in the past! In my case I can`t remember right now as I didn`t pay close attention (working OK, so you don`t check too close) Duratec normal & Zetec normal may be different anyways..... `fraid I`ll have to recheck my "normal" in a bit for a better reference, 700 does sound right for an automatic when in gear, 6-700 is my memory for "normal" in that case when fully warmed up.... Good output at idle is the whole point to alternators, as opposed to old time generators, interesting that you get a dramatic increase in output between 700 & 900. I`ll get back when I recheck idle after fully warm when driven.... maybe get out the voltmeter for another reference set of #`s.
 
#24 ·
Posted via FF MobileOkay, after a drive to warm up I`m getting 14.5 volts at about 700 rpm, so the higher idle was due to not fully warm & output is OK at low rpm - no help, but a better reference than my false idle #`s.
 
#25 · (Edited)
So I installed a new battery today. Luckily my old one was still under the 2 year warranty so the new one was an even exchange and didn't cost me a cent out of pocket.

Brought it home, put it on the trickle charger (who knows how long it sat on the shelf at the store), let it fully charge, and then installed it on the car. With the car turned off battery voltage read 12.85v. Start car (engine warm, no lights or accessories on) and charging voltage is still under 13v at idle. Turned on lights and everything electrical I could turn on and charging voltage falls below 12.6v at idle.

Voltage quickly climbs to 13.5-13.6v with everything electrical ON at about 900-1000rpm. Same RPM with everything turned off yields about 14.6v

I guess this H.O. alternator I bought really does have to spin at a higher RPM before it does anything :(
 
#26 ·
Posted via FF MobileShucks..... well keep an eye on it, should charge enough to be OK as it`s at least maintaining battery voltage at idle with a load - not dropping below to indicate a draw on the battery at idle. And it charges fine once off idle to recharge the batt. from starting loads... Not tragic, just won`t recharge appreciably at idle...
 
#27 ·
Last time i saw numbers like that, my alternator was breathing its last. Then again, the low voltage at idle was accompanied by the requisite "moan" alt's tend to make when they die...
 
#28 ·
Kind of late for the original poster, but I just had the same issue of the battery light being on for no reason. My battery is only a year old, and the alternator is outputting 14.4v. The cause for my car was fuse 10 in the fuse box under the hood. It is for the battery sensor, diagnostic plug. The fuse was blown, put in a new one and the light went out. I wonder if it blew because my drivers side lock actuator went out and blew the fuse for that. It caused the dome light to dim a lot, and the others doors unlocked real slow. I need to get an actuator and replace it.
 
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