Intermittent "Check Charging System"

[Bolt snapper]

I've read through a number of threads on here and it seems like there isn't just one common problem, so hoping you can help point me in the right direction.

Here goes: 2004 5.4 with 176k. Beginning last night - only at startup - the "Check Charging System" message displays and the battery light goes on and off. After pulling out of the driveway, both warnings clear and all seems normal. 15 minute drive. Stop and shut off for 10 minutes waiting for kid to get out of practice. At startup, once again, a brief chime of the message, but the drive home was uneventful.

This morning, same thing - except the message stayed on for a few blocks, then cleared. I came back home after 15 minutes of driving and checked voltage at battery while running: 14v plus (I think in the range of 14.3?). Drove another 15 minutes to work and while idling at a stop light, message came back (and I think I heard the blower motor slow down). The dash gauge seems to be normal and doesn't fluctuate. I popped the hood real quick (message and battery light are still on at this point), and measure voltage again. This time it's at 12v plus change.

Does this sound symptomatic of a failing alternator? Any other likely culprits I could quickly rule out (my understanding of electronics and circuitry is minimal, so my diagnostic skills are severely handicapped)?

Any help you can give would be greatly appreciated!

 

[Plati]

I had a similar problem on my 2003. The alternator couldn't keep up with the extra drain of headlights (when they were on). It was diagnosed at the shop by starting vehicle, measure charging voltage, turn headlights on and observed that the voltage dropped. Lowering windows is also a drain on system. I could see headlights were dim also. Replacing the alternator fixed that.

there are things other than alternator that your problem could be

 

[Hamfisted]

How old is the battery? It could be a combination of old battery and old alternator but more than likely it's the old alternator.
I would say start with a new Motorcraft alternator from Rock Auto (stick with Motorcraft for this part...). Clean your battery terminals when you replace the alternator too.

https://www.rockauto.com/en/catalog...427756,electrical,alternator+/+generator,2412

 

[99WhiteC5Coupe]

I would start with the basics.

Remove and clean the battery cable terminal connectors and the battery terminals, using a battery cleaning brush tool.

Inspect the battery cables - any corrosion and/or swelling - especially near the connector ends?

Inspect the ground cable (opposite of the battery) for a clean and tight ground connection.

Reconnect and see if the message recurs.

 

[Bolt snapper]

Thanks, guys! The battery is a year old. Could be a factor but it would be a bit surprising.

One more extremely dumb question: How do I know if I have the 110A or the 135A alternator (without pulling it out of the vehicle)?

 

[Hamfisted]

If you have the factory navigation system or 6 CD stereo system you most likely have a 135 amp alternator.

Thanks, guys! The battery is a year old. Could be a factor but it would be a bit surprising.

One more extremely dumb question: How do I know if I have the 110A or the 135A alternator (without pulling it out of the vehicle)?

 

[Bolt snapper]

It doesn't have either now. I would guess that it never did (was the 6 changer in the dash?). Radio's been replaced with an aftermarket.

 

[stamp11127]

Do you want to diagnose the problem or toss parts until you get lucky?

Here are the diagrams for a 2004 4.6. The 5.4 should be similar if not identical.

If you are diagnosing, check voltage at the alternator output stud and alternator case. Should be above 12.6v with engine at idle. Red lead goes on the stud, black on the case. If the voltage is not in the range of 13.5-14.5 then you may have failed alternator internal components, harness issues between the alternator and pcm or failed pcm. The voltage regulator has been replaced with pcm control on this year.

 

[Bolt snapper]

I appreciate that! I'll run that check this morning before I go any further with it. Thanks for taking the time to respond and provide the attachment!

 

[AftonJay]

or just go to advance or autozone or any number of places that do either free or very cheap charging system checks, that include battery, alternator and sometimes starter.