"check charging system" intermittent computer display - Ford Mustang Forum
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post #1 of 3 (permalink) Old 01-29-2014 Thread Starter
buggeroff69's Avatar
Joined: Sep 2011
Location: Natick
Posts: 2
"check charging system" intermittent computer display

This is an 05 Mustang GT convert, 66K miles. Only elec. mods were a "Battery Saver" low voltage interrupter, which I put on b/c I use a heat pad (don't have heated seats). I guess those items are a bit stuffy, and if I didn't use the car for 3-5days, it'd be cutting off ignition, even though I could start w. it removed at around 11.55v!
I also have a Pioneer AVIC-930 NAV, which I assumed was somehow putting some constant tricle flow out of the battery with the above scenario, so the Best Geek said the solution was simply to connect one wire direct to the battery. Don't ask me which wire, but the car would act like it was losing elec. power just taking turns thereafter, until I permanently removed the battery saver device. Since then, as it has gotten colder (Boston DUHH), I have been getting periodic "check charging system" on the tach systems status LED readout ribbon...usually within 15" of start up (no weird low elec energy turnover I can sense, tho). Running the stupid "check systems" button actually brings up "charging system ok"! Taking car to Autozone with their battery plug in showed 11.88v, and they told me to drive the S--T out of the car, they couldn't tell if it was the alternator.
I have a trickle charger, and used it after their advice a few times, which seemed to delay but not eliminate the stupid warning.
Sears did a Sears quality (aka cursory) battery test, said it was beyond their brainpower and sent me out. I've been calling FORD dealers who generally want $120 or more or diagnostics per hour. Some sales reps say to ignore it until it goes FUBAR. I am leaning towards that-it's an annoyance without any viable fault line, but I'm still blabbing here to see if anyone knows any ways around this stupid warning computer sign, or what is going on, as I've read there are a lot of folks that can't trace this but for 100's of hours or bucks. I don't think it's the radio. It might be aliens, or Daft Punk, but I'd like to be rid of it before I sell the car in a year or 3!

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post #2 of 3 (permalink) Old 01-29-2014
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Joined: Oct 2007
Location: Alexandria
Posts: 465
I never had alternator problems on my 2005 GT, but several posters on this site have said they needed to replace the alternator on their Mustangs. It sounds like yours may be getting weak, but its hard to tell how long it will last.

With the engine running, HVAC blower on high and headlights on, it should be able to maintain approximately 13.8 volts at almost any speed above idle (it probably puts out full output at about 1500 rpm and up, but I would have to check the specs). If you can get that 13.8 volts out when running, then it might just be a weak battery.

Most of the auto store battery and alternator testers only make a very gross-level measurement of good/bad. I had an alternator in my GMC truck that would only put out about 10.5-11.0 volts if the headlights and HVAC were on, but Autozone still showed it as good because they never tested it with a load. I finally put a separate voltmeter gauge on it and watched it during normal driving. I was driving to work in the dark in the winter (lights and HVAC on), so the battery never really got a full charge in normal use. Replacing the alternator solved all my charging and starting problems.


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post #3 of 3 (permalink) Old 01-29-2014
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Hellraiser456's Avatar
Joined: Feb 2009
Location: Calgary
Posts: 236
Radios will draw a small current for memory...its really small though. You could have hooked it up backwards, bu then the radio won't turn off with the ignition. By the sounds of it, its not the radio

If the battery checks out fine, check the alt. I have heard of wiring and other connections around the alternator going bad, especially in earlier years. Check the wires may lead you to your problem. Otherwise, these cars have somewhat weak alternator
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