battery light on - battery tests good and alternator charging ok

[DK327]

Hello all,

A few days ago the battery light on the dash came on on my 06 V8 T4R. I checked scangauge3 and it appears the alternator is charging the battery just fine at 13.8v when the vehicle is on. It shows some fluctuation 13.6v-14v with scangauge but remains solid 13.8v with something else plugged into the cig lighter showing voltage. Resting batt voltage is 12.8v. No issues starting the vehicle. I tested the battery with a tester and it shows good at 87% health, 98% charge. I checked the 7.5a ALT-S fuse and it's good. I checked the load with radio, ac and lights on and it's only dropping to 13.7v.

This started a few days ago after I got the vehicle undercoated and noticed they had sprayed some shit on the battery terminals, probably anti corrosion or rust preventative. I unhooked the terminals and wiped all that off with break cleaner and reconnected everything but battery light still remains illuminated.

I quickly looked at the alternator from above and it looks like they didn't spray anything on or near it but I can't see the power cable connecting to the alternator from top of the engine and i don't really want to go below the engine since they just coated it and it's sticky with black goo. I think the alternator is accessible via the passenger side wheel well but not sure if i can access the wiring and the terminal through there, didn't check yet.

Anything else I should check that anyone can think of? Any help is much appreciated!

 

[ArthurKotb]

From Google AI:

The dashboard battery light is triggered by a voltage imbalance in the charging circuit, not just raw voltage. Because your 4Runner is putting out 13.8 V and resting at 12.7 V, the primary alternator winding is working, but a secondary circuit fault is likely keeping the light illuminated.

Failing Alternator Diode: The alternator contains diodes that convert AC to DC power. If one diode blows, the alternator can still produce 13.8 V to 14 V but will produce AC "ripple," causing the warning light to stay on

Alternator Wiring Pigtail: A common issue on these models is a damaged, corroded, or broken excitation/sense wire (often the white or yellow/green wire) in the alternator wiring harness. If the signal doesn't reach the ECU, the dash light stays on

Internal Voltage Regulator: The built-in regulator might be struggling to manage the field current or has worn internal brushes, allowing the alternator to run but failing the system's circuit check

Corroded Terminals or Grounds: Even if voltage looks good, high resistance from corrosion at the battery terminals or a loose main engine ground strap can trigger a voltage drop, turning on the light

Loose Serpentine Belt: A slipping or worn drive belt can cause the alternator to spin too slowly at idle, lowering output and tripping the dash indicator