I have a 2006 Silverado 1500 LT Extended Cab with the 4.8 V8 with 135,000 miles. I have been dealing with a issue for alittle over a year now of getting a SCS battery light either after startup and idling for about 20ish seconds or if you put in in drive and it comes on after about 5 or so minutes, also have been battling corrosion on only the positive battery terminal. Whatever the issue is It absolutely killed a 2 year old duralast battery.
Things I’ve done and replaced: new oem generator battery control module, new battery, cleaned the grounds for the negative terminal that go to the link between alt and battery and the one in the block and body, unplugged my 2 pin connector for the alt to have it default to the 13.7 voltage charging, my gauge spends most its time above 14 volts like 3 little lines above 14 and with my autel bi direction I get something about a f terminal fault or low voltage, the only thing I haven’t done is replace the alt because it is still charging and whenever I test it, it tests good a 2500rpm hold test. And added a ground strap from body to engine block also cause the original one behind the motor was to much of a pain in the butt to get off. P0625 is the code and I’ve checked voltages and things with multimeter and my scanner and cans see anything abnormal. Any knowledge is appreciated

 

Testing the alternator @ 2500 RPM can produce a deceiving result, especially if you’re relying on scan tool data alone. All alternators should be capable of running any and all loads at idle speed.

2 Test methods that should provide clear results:

1) Preferred method NOTE: The following tests require good, stable battery & meter connections or the results will not be dependable. NOTE 2: If side post battery, replace the bolts with 3/8 x 16 hex bolt & clamping nut just for testing - those OEM bolts are a joke.

With the engine idling @ operating temperature, first check the voltage output of the alternator at the battery terminals while turning on & activating as many electrical loads as possible.

The following list has never failed me in assessing the charging capacity of an alternator:

-any & all heater grids (rear defrost, seat or steering wheel heat)
-blower fan on high, AC on [defrost mode in winter]
-wipers on HI if possible (only during rain/wet snow)
-foot on brake in Reverse
-HI beams on
-phone on charger
-cabin lights on at maximum brightness
-audio system on (and/or cranked to full volume if tolerable)
-operating pairs of windows up & down at the same time (if equipped with power windows).

Expect the voltage to drop momentarily to between 11.8 - 12.5 vdc as more loads are added - but it should quickly recover to above 13.0 vdc and stabilize after each accessory.

If It drops below 11.8 vdc at any time, then check the voltage drop of the charging cable (B+ stud @ alternator to B+ cable clamp) and primary ground cable (B- stud on block to B- cable clamp) with all the same accessory loads.

Any drop more than 0.5 vdc across either cable is reason for replacement; then recheck charging voltage at battery with loads on. Replace if not staying above 12.0 vdc at all times.

2) Backup method in the event that the preferred method is inconclusive. NOTE: There is the possibility of damage to PCM or other modules when performing this test. It is not recommended by GM to do this test for that reason. Perform this test at your own risk/discretion.

That said, in the few times I’ve had to resort to this, it’s not caused any serious problems with modules that I’m aware of.

With the engine idling at operating temp & basic loads (such as DRL’s) on, disconnect & isolate the B negative cable to prevent accidental battery contact.

If it stalls within a few minutes, the alternator is done.

If it continues to run, there’s no reason to suspect the alternator is on its way out. There’s likely a wiring problem between the alternator & charging module.

Recurring corrosion build up is another indication the cable(s) need replacement, but as long as the connection between the cable & battery is clean, the corrosion shouldn’t affect the test results.

Neutralize the acid with white vinegar or 50/50 mix of baking soda/water then rinse with water and dry with compressed air.

 

You need to test the alternator for AC ripple voltage. Ideally, the AC ripple voltage should be less than 0.050 V AC (or 50 mV AC). You can test it using a Digital Multi-Meter (DMM) set to AC mode and the voltage range to either the lowest scale or to the AC mV scale.

With the engine running and the high beam headlights on, connect one of the DMM's test leads to the battery's negative terminal and then the other test lead to the BATT terminal on the back of the alternator. If the reading on the DMM is greater than 50 milliVolts (50 mV or 0.050 V AC) then you should get a new alternator because one or more of the internal diodes is bad. Also, AC ripple voltage is bad for the battery.

 

Thank you will be giving this a shot today

 

thank you I will be giving this a shot today also and will update the thread with my findings

 

thank your for your suggestion I was definitely having ac current/ripple into the battery, a doide test confirmed the diodes where not allowing back flow, but not properly converting the AC into DC, new alternator fixed it, and I ordered and new rectifier and voltage regulator to rebuild my original AC delco, I just got this cheap A-1premium alternator for the mean time

 

Congrats! Batteries do not like AC ripple and the more AC ripple voltage there is, the shorter the battery's life will be.

Replacing the rectifier assembly and voltage regulator are not that difficult. You might want to replace the brushes as well. If you can, clean and repack the bearings as well.

Good Luck!

 

thanks, most definitely will look into to that