NEED HELP Charging System Low Voltage

[Robbabob]

Charging system is low at about 1/4, after it's been fine for months. Trying to figure out what to check or test, and then I remembered the Firestone dealer had replaced our battery after they let ours die about 3-4 months ago.

While searching this site for possible solutions, I kept finding notes about a "wrong sized battery" being a possible cause to their issues. Made me think to take a picture of what they put in and ask y'all if after a few months of running the one they installed, if it may be the culprit. I really don't want to start replacing the alternator or battery if something I can debug to look for the actual issue.

Your input is always appreciated!

 

[Mooseman]

Could just be the alternator. Did you test it?

 

[littleblazer]

I'd double check the pinout on the trailblazer but this is the right way to do it. Also works on the older 2 pin guys on the older cars using the si style alterators. Also battery seems to be right 75/78 are about the same size iirc.

 

[Robbabob]

Mooseman: Testing the alternator is merely hooking up the meter and measuring the voltage into the battery, right?

LB: I need to do the pin-out check to confirm if the PCM is signaling for the alternator to come on?

 

[littleblazer]

Yes. I don't know if the plug on the full size is the same or not so you'd have to double check the pinout. Chances are the alternator is dying but better safe than sorry. Check voltage at alternator output terminal, check trigger just to make sure.

 

[Mounce]

I vote alternator. No matter the battery the alternator should still produce proper voltage. Battery can be completely shot but jump it off and vehicle will run fine.

However it does call for a group 78 battery.

 

[Robbabob]

The voltage with the engine running is still only 10 volts (checked at the battery).

Alright guys, Thanks! I'll check on it tomorrow and in the mean time, the wifey gets to stay close to home (and on the plug charger over nights).

I'll follow up with the status and results.

 

[Mooseman]

I say right now that likely your alternator is shot but to confirm, you have to take it out and take it to a parts store to bench test it. Also check to be sure the alternator connector is in fully. Had that happen to me once where it wasn't fully clipped in.

 

[Reprise]

A hopefully helpful suggestion...

If you do (likely) replace the alternator, charge the battery before starting up the truck - it will be a lot less taxing to the new alternator, depending on condition of the battery.

Might also be good to have a load test done on the battery afterward, especially if it's more than a couple of years old. The wife will thank you for it

 

[Drec]

Last year my wife and I were on a trip in our 2005 Silverado and I noticed a low voltage situation with the voltmeter. We were about 800 miles away from home when we reached Reno. I had the battery and charging system checked out; which everything checked out good. So I watched for the rest of the trip. After returning home the battery stared going dead over night, so I replaced the battery. Then the new battery started going dead, but the alternator checked out fine. Then I noticed I noticed some corrosion on the positive cable where the 10 ga pigtail part of the cable goes back to some other circuits. I replaced the positive cable and pigtail and the problem went away.

This Silverado has over 200k on it with the original alternator. The battery had been replaced a couple of times before though.

 

[mrrsm]

And on (-)The Ground" Side(-) of this matter... again... Drew is supported in his idea of using the Right Metering Tool to discover problems that are both vexing AND invisible. In this video... we get to see How to Use a Volt Meter to Statically and Dynamically look for problems in the Grounding System using Voltage Drops to discover ...WHICH Ground is The BAD Ground?