'08 Silverado alternator issues

[327chevy]

While driving my truck this evening I noticed the amp gauge was showing discharge signaling perhaps a fault in the alternator.I got to my destination without issue,shut the truck off,started it later to head home.The gauge read normal for a couple of minutes then showed discharge again and stayed that way til I got home.Once I got home I left the engine running and got my volt metre,put the probes across the battery posts and sure enough the metre was reading only 12.8 volts.I shut the engine off,restarted it and measured the voltage drop again,14.6vdc,hmm.

The battery is only about 4 months old and is the heavier duty GM one so I'm thinking that part is fine so this leads me to believe the alternator has something funky going on inside it.

My truck isn't a daily driver,I walk to work and only drive the truck a couple of times a week normally.This issue with the amp gauge showing discharge had cropped up once before but went away and I never thought of it again until tonight.

Any thoughts?I was thinking of pulling it off tomorrow night after work,popping it apart and seeing if maybe there's just some corrosion that needs to be cleaned up,if I'm lucky.Just how big a job is it to take one of these alternators apart?I've had lots of the older ones apart,it seemed like I was changing diode trios and regulators every time I turned around.

[aleekat]

Voltmeter

[j cAT]

Originally Posted by 327chevy

While driving my truck this evening I noticed the amp gauge was showing discharge signaling perhaps a fault in the alternator.I got to my destination without issue,shut the truck off,started it later to head home.The gauge read normal for a couple of minutes then showed discharge again and stayed that way til I got home.Once I got home I left the engine running and got my volt metre,put the probes across the battery posts and sure enough the metre was reading only 12.8 volts.I shut the engine off,restarted it and measured the voltage drop again,14.6vdc,hmm.

The battery is only about 4 months old and is the heavier duty GM one so I'm thinking that part is fine so this leads me to believe the alternator has something funky going on inside it.

My truck isn't a daily driver,I walk to work and only drive the truck a couple of times a week normally.This issue with the amp gauge showing discharge had cropped up once before but went away and I never thought of it again until tonight.

Any thoughts?I was thinking of pulling it off tomorrow night after work,popping it apart and seeing if maybe there's just some corrosion that needs to be cleaned up,if I'm lucky.Just how big a job is it to take one of these alternators apart?I've had lots of the older ones apart,it seemed like I was changing diode trios and regulators every time I turned around.

with your vehicle you may have the fuel saving alternator setup. see if this vehicle has this . now when the discharge shows up put the ac on to max ,headlights on to create a larger electrical load .. if the alternator now shows a charge then you are ok. this is normal..

on first starting this discharge should never show... that is not normal..

GM did this to increase MPG at the expense of the battery and the alternator..

[327chevy]

How would I go about telling if this truck has this fuel saving alternator setup?

[gmtech1]

It'll have a current sensor on the negative battery cable at the battery. the ECM monitors. The ECM commands more or less current as the electrical load changes.

[327chevy]

Ok So I never noticed anything on the negative cable when I changed the battery so I'm going to just say that I don't have that odd type of setup.

[327chevy]

I forgot to mention this in my original post but the fluctuating volt gauge was never present before except for the one other time I did mention so what ever is going on with my charging system has just started getting worse.So I still would like to know how hard it is to snap the alternator apart.I'm an electronics technician by training so I have the tools most likely to be needed plus I like to consider myself fairly mechanical so this really shouldn't be a big deal.

[j cAT]

Originally Posted by 327chevy

I forgot to mention this in my original post but the fluctuating volt gauge was never present before except for the one other time I did mention so what ever is going on with my charging system has just started getting worse.So I still would like to know how hard it is to snap the alternator apart.I'm an electronics technician by training so I have the tools most likely to be needed plus I like to consider myself fairly mechanical so this really shouldn't be a big deal.

if you have the old style alternator with this 2008 I would be surprised.

but with not knowing the engine in it I guess it is a possibility.

my experience with these old style alternators is that the regulator assy of the alternator gets corroded . this is the common failure under normal proper usage..

problem is finding these regulators .. replacing them is all not that easy. I did buy a new alternator rather than go thru the repair of the old. .reason is these run much much hotter than the 1980-1990 model years so that the windings get heat damaged .

[327chevy]

Good to know,thanks.
I just called my local auto parts store and there's 3 different alternators listed for this truck,a 150 amp,140 amp and a 125 amp one.The 125 amp one is apparently made by Bosch where the other 2 are Delco ones so now I gotta find out which one I have.

[327chevy]

Well I guess it pays to be observant and I freely admit at times I'm not very.So I was looking things over on my truck earlier and lo and behold there is the current sensor on the negative cable.If I had ever seen this before I never took notice of it.Anyway I just can't say as I've ever noticed the volt gauge dropping off like it did the other day but I guess this is normal with the current sensor so I guess I'll leave well enough alone for now and save myself some money.

[j cAT]

Originally Posted by 327chevy

Well I guess it pays to be observant and I freely admit at times I'm not very.So I was looking things over on my truck earlier and lo and behold there is the current sensor on the negative cable.If I had ever seen this before I never took notice of it.Anyway I just can't say as I've ever noticed the volt gauge dropping off like it did the other day but I guess this is normal with the current sensor so I guess I'll leave well enough alone for now and save myself some money.

so now with that determined my guess is ,,, this current sensor is defective. go to the dealership and ask for part number and the TSB about this..

you will find the the replacement has a new part number, and is different, because the OEM as built sensor is MORE GM crap !

with the correct part number find the part on line for much cheaper than dealership///.. this is a 100% fail rate with the OEM original current sensor part..

[327chevy]

Good to know,thanks.

[327chevy]

Is there any way to bypass the sensor? It just stands to reason that when the volt gauge drops off like it is now that the battery is actually discharging and sooner or later this will leave me stranded.

[j cAT]

Originally Posted by 327chevy

Is there any way to bypass the sensor? It just stands to reason that when the volt gauge drops off like it is now that the battery is actually discharging and sooner or later this will leave me stranded.

no ..many have tried ... PCM/BCM all programed for this ...

this can be had for less than 100..so I was told..

[327chevy]

Originally Posted by j cAT

so now with that determined my guess is ,,, this current sensor is defective. go to the dealership and ask for part number and the TSB about this..

you will find the the replacement has a new part number, and is different, because the OEM as built sensor is MORE GM crap !

with the correct part number find the part on line for much cheaper than dealership///.. this is a 100% fail rate with the OEM original current sensor part..

Would this service bulletin be the same in Canada as it is there in the US? It'll be Monday before I can find a part number from a dealer and I just would like to have as much info as possible before I call a parts guy and have him give me the run around about " no such tech bulletin" .