Charging System Light On

20

Asked by Feb 16, 2017 at 08:36 PM about the 2003 Ford F-150 Lariat Crew Cab 4WD SB

Question type: Maintenance & Repair

Hi all,
The battery/charging system light came on
in my truck. One other time it came on and
went right back off again. Interestingly this
happened in the same place today as it did
before, on a rough road. Anyway this time
the light came on and stayed on. It has a 5
year battery and it is just past the 5 year
mark. I checked the battery with the engine
off and got 12.9 volts. With the engine
running it read 14.39 volts. It starts and
runs fine. Would the readings I got mean
the alternator is okay? I was also
wondering if the rough road could have
caused a connection to come loose.
Anyone have any ideas about what's going
on with my truck? Thank you.

15 Answers

17,725

Alt should be fine its in range but may be going bad so may want to have it load tested a good parts store can do that, Battery volts is near o.k. but a tad weak should be 13.2 but otherwise it could be a loose or corroded terminal & terminal wire or other connection loose or even a bad or loose engine to frame ground.

20

Thank you for your help. I was wondering if there was a way to tell if the alternator was on its way out, so now I know to have the charging system tested under load. I'll let you know what I find out. Of course I am hoping for a loose connection, but will be surprised if I am that lucky!

17,725

The alternator will more than likely need to be pulled off to test at (Auto-zone or others) unless they have new equipment.

20

Thanks, glad you mentioned that. I'll make some calls to see if anyone around here can do it while still on the truck. Otherwise, is it very difficult to remove? I have a code reader. Could that hellp to isolate the problem?

19,810

You can preform a simple test yourself if you have a digital multimeter. Start the vehicle, let it idle, and look the voltage reading. It should 13 to 14.5 volts on a fully charged battery. If you get that reading begin turning on electrical items. Headlights, fan, radio, interior lights, etc. and leave then on a minute or two. Now check the voltage again. If the voltage appears to be dropping, your alternator could be in need of replacing. I doubt any friends or neighbors will have a battery charger which will check the alternator by applying a load while on the battery. You will either have to bring the car to a shop for testing, or remove the alternator and bring it to autozone who will test it for free.

20

Thanks for your answer OJ. I am guessing that if the home test checks out it is probably not the alternator, and I I should be looking for a loose wire or bad connection?

19,810

Have autozone check the vehicle for any fault codes. YOu could have a problem with the voltage regulator which is within the alternator case. A light remaining on while the alternator is out putting charging voltage can be a sign of a defective regulator. Google Ford PCM controlled Alternator. I am sure you will find a few videos covering your particular problem. Also, the plug connection on the top of the alternator. One of the wires reports back to the PCM it is responding to input from the PCM and trying to charge. Make sure one of those wires is not pulled out of its electrical plug connection.

20

Thsnk you again, OJ. I wouldn't be surprised if that plug or some other connection has come loose. The road to my house is like a washboard. The truck is the off-road model, and the suspension is really stiff. Will get to work today on checking it out. I will let you know what I find out.

20

Well, the plot thickens. Today I went out and started the truck and the light has gone out. I ran the truck for awhile, and it didn't come back on. Still getting a reading of 14.3 at idle. So far I have not found any loose wires under the hood. I guess the next thing would be to check for a loose wire under the dash.

19,810

Found this video which may help. www.youtube.com/watch? v=pBseSRahN91 showing testing procedure for PCM controlled Ford Alternator. The idiot light on the dash is activated by the PCM. The PCM is getting a non-charge/overcharge reading and initiating the light. You should be able to check the two outer wires of the 3 wire terminal with a digital multi-meter. One should give you the same line voltage 14.whatever volts you get at the battery. The outer line is a return signal from the alternator to the PCM indicating the alternator is try to do what PCM suggests, which the alternator receives via the middle wire. If you check when light is off, you will get a return signal to the PCM. Check when the light is again lit, and if there is no voltage/signal being sent back to the PCM then the internal voltage regular is probably bad or going out. Since the light goes on and off, have the codes read at Autozone and see if there are any stored concerning the charging system. Hope the video helps.

20

Hi OJ, I couldn't find the video from the link or by entering the address manually, but I think I get the basic idea from your instructions. I don't have a lot of experience using the multimeter. I am guessing that the meter should be set the same as when I used it at the battery. I am not sure how to use it at the alternator. I hate to ask such a basic question, but could you give me step by step how to use the meter at the alternator, like where the probes are placed. I am thinking the positive goes on the unplugged wire I am testing, but not sure where the negative goes.Thanks much.

19,810

Did you google "Ford PCM controlled alternator"? You should get a few video responses. The procedure is quite easy, but if the light is off right now, you will not see any fault. Try googling it first as it would be quite a bit of typing. The basics are you will be back probing the three wire terminal connection where it plugs into the top of the alternator. You will be checking for voltage. Battery voltage on one outside wire and a a response voltage back to the PCM from the other wire. If there is no voltage on the return wire, the internal regulator is bad. As for hot to use the multi-meter try googling that also for a video "How to use a multimeter". Let me know.

20

Hi OJ, I did google, but I didn't see anything about my particular situation. I guess, though, the videos don't have to be for my particular problem as long as it shows the testing procedure. I will try doing a more general search. Next time I get to town, I will have O'Reilley's check for codes. I live pretty far out in the country. I also remember I went thru a bit of water the last time the light came on. This may be purely coincidental though. This truck has been rebuilt and we have found a few "shortcuts" the rebuilder used on some connections and they have come loose. The ones we found have been fixed. I will do a more thorough search on the PCM and how to use the multimeter. I am going to carry the meter with me so I can test when the light comes on again. I appreciate your help and will keep you posted. Thanks.

20

Hi OJ, Could a loose connection that allowed the signal for the turn system to work or not depending on the position of the wire cause the charging system light to go on and off? I haven't been able to get to town yet to find out if there are codes. My fingers are crossed hoping that I have stumbled acrossed the cause of my problem. Thanks again.

20

Sorry for saying the "the turn system" when I meant the"turn signal". So the turn signal worked intermittently depending on the position of the wire.

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