2010 F150 Lariat 5.4L Battery warning and power loss

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Jun 17, 2026 | 10:45 PM

bignicksnr

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4th Gear

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2010 F150 Lariat 5.4L Battery warning and power loss

Lots of old threads - one exactly like mine, but starting a new one:

2010 F-150 Lariat 5.4L, 2 year old battery, 157K miles
All of a sudden the alternator stopped charging. Went through the following:

Checked & cleaned grounds
Checked and cleaned battery without load and under load
traced all wires from alternator to battery to PCM. All had continuity with no breaks, burns, or loose connections, including blue charging wire.
Could not find any burned fuses
Verified voltages with voltmeter to find the alternator/regulator would not charge. removed and took to O'Reilly. They checked and verified it failed.
- **During all the above trial & error, the battery drained down to ~ 10.9v
Purchased and installed brand new, OEM Motorcraft alternator
Performed reset procedure (multiple times) - 5x high beam flash & 3x brake press. CEL symbol flashed 7-8 times. Once it flashed 4x.
Charges between 13.8-14.3v.
- Battery recharged to 12.3v (Charged separately from alt). Handles load fine with minimal drop off.
Still get battery symbol warning & went into limp mode TWICE on highway!
After each time it shut off in limp mode, I did the reset procedure again and it ran fine with no issues until I shut it off and restarted.

Tried Forscan until I realized there is no Battery Management on the 2010 so Forscan is useless.

Jun 18, 2026 | 03:26 PM

bignicksnr

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PCM Reset

I THINK I figured it out. I saw a stray youtube short vid about disconnecting the battery completely for at least 30 min. Reconnect, key on without start for 10 sec, then start and drive stop & go for 30 min. So far, so good. I hope like hell this does it!

Today | 02:27 PM

bignicksnr

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Joined: Jun 2026

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I was wrong but...

Quote:

Originally Posted by bignicksnr

So this did NOT fix the issue. HOWEVER, I have narrowed it down. If the alternator starts charging over 13.9v, I get the warning - constantly. Once it drops down to 13.9 or below, everything is fine. I've tested that 3x and there's no doubt that is the issue, but I have no clue how to fix that. Is there a way in FORscan to reset the charging threshold? Any other ideas??