Battery Charge light on, system is charging

[rray]

2004 Expedition 5.4. Battery light came on, with the original OEM alternator, however system seemed to be charging. PEP boys said it needed an alternator, replaced alternator, light still on, battery is good, alternator is putting out between 13.8 and 14 volts under load. Voltage drops to 10.6 on while starting. Cleaned all connections, battery, fusible. No luck battery light stays on. I've seen other threads where they replaced the fusible link, but it also said it usually breaks in the open position?

Any idea's... Thank you!

 

[Plati]

for reference ... my 2003 XLT 5.4 rustbucket ... I measure 12.2V at battery terminals before starting. Voltage drops to 10.8 for a millisecond while staring then goes to 14.2V after starting and running 20 seconds. Turn high beams on and voltage drops to 14.0V

I was under the impression fusible links can be "bad" but not open circuit ... have resistance with voltage drop

Does it work fine except for the battery light, which means charging system problem? Is that light on all the time or off & on?

 

[17LimitedExpy]

Maybe ask Pep Boys if they can swap in a new battery to see if that is the problem.

 

[rray]

I replaced the alternator based on what PEP boys told me. However, that was not the problem. The system works fine. My numbers are about the same as you posted. So battery is good and so is alternator. The light stays on all the time. I did not check resistance between the batter and the alternator through the fusible link, but visual observation looks good. I did however check voltage between pos on battery and pos on alternator. Running and not running. There is about a .10 difference in voltage from the alternator output to the battery pos lead. I've ordered a fusible link and I'm going to replace that. I will post again the results of that part exchange.

 

[rray]

Battery is fine, charging system is fine under no load and under a full electrical load. Light just stays on.

 

[Plati]

there was a previous post here
http://www.expeditionforum.com/threads/battery-light-stays-on-but-charges-fine.31792/

fusible link replacement ... different year

 

[stamp11127]

If I remember correctly that year uses a pcm controlled alternator. There is a recent thread with the same problem that I posted the wiring diagrams.
Even though it is charging it isn't communicating correctly with the pcm. Pcm turns on the light.

 

[Ed_Strong]

If I remember correctly that year uses a pcm controlled alternator. There is a recent thread with the same problem that I posted the wiring diagrams.
Even though it is charging it isn't communicating correctly with the pcm. Pcm turns on the light.

I agree %100 with stamp11127:
I had the exact same issue he is describing here. This re-manufactured Alternators are being restored with older components that are not compatible with this "plug and play" electrical systems in newer vehicles. In this case the older Voltage Regulator does not communicate with the PCM setting the warning light on the dash or setting a DTC since the PCM has no way to monitor, control and regulate the voltage coming out of the Alternator.

 

[rray]

I keep hearing the PCM may be the problem. The light came on with the OEM alternator which we found was working, after I replaced it. I kept the new alternator on since the vehicle has over 160,000 miles on it. I figured it could not hurt. Is there a software update to the PCM from Ford that may turn the light out? As I stated earlier, I'm replacing the fusible link as soon as it arrives. Will keep posting till solution is found.

 

[Plati]

Here's the post stamp cited with wiring diagrams/pcm communication .... if its the right year?
http://www.expeditionforum.com/threads/charging-system.35838/#post-304461

some good info but this is getting a bit knotted up (methinks)

the key is a disciplined diagnosis (sorry to state the obvious) .....
what exactly did pep boys find was not working right when they decided to replace the alternator? what changed (if anything) with new alternator? if EVERYTHING is exactly the same with new alternator then they probably should put the old one back in and refund $$$??? then chase down the original problem

it is possible to have more than one problem at the same time (sometimes 3), especially with parts swap -- confounding diagnosis. could be a connection was defective causing original problem then new alternator has that pcm/communication issue so now 2 problems. not saying thats the case, just possible

i'm not really knowledgeable about that PCM communication concern but if there was no communication between pcm and alternator then it would seem that would be easy to observe by measuring voltages & signals, is that true?

i would not replace fusible link without diagnosing an obvious problem with it, what is the observed problem that shows fusible link is bad? the charging light coming on cant prove fusible link is bad, other evidence needed to indicate that

a skilled mechanic can use tools like in this video, along with knowledge of the system to find out whats wrong

i'm not a big fan of swapping parts (like alternator, battery, fusible link) without hard evidence that they are bad (how/why)... and then if you do, hard evidence of a problem corrected by the replacement part

hope some of this helps