Silverado Alternator not putting out proper volts - Already changed the alternator...

[JimPratz]

rhandwor

I will check into the rebuild idea, I've heard of people doing this before. I'm the type of person that notices every change in a vehicle and as I said, in the beginning it never dropped below 13.xx, no matter what the load, and GM said it's a variable alternator, but down to 11.xx volts is WAY TO LOW, and it's too frequantly and sometimes doesn't come back up above 12.xx Volts; which is too low, the load isn't changing (I always run the same things (all factory (radio, A/C, headlights at most) ( live in Florida so Cold isn't an issue, heat could be but not likely, I had a 2004 truck same model and never an issue and a buddy of mine has a 2007 same model and no issues.


j cAT



you have a 2008 silverado this is quite a bit different than the 1999-2006 models. some of these newer body style silverado trucks have MPG enhancer PCM in them. with this the voltage will drop down to 12 volts then shoot up to 14 volts. this is to according to GM increase the MPG.

This is true and mine does too I'm sure ; however; it sometimes never goes back up above 12.xx volts (unless I restart the truck as explained in my prev post...)


did the dealership say it is normal to have 5 batteries replaced. even if the alternator was not putting out power all the time the batteries should not get damaged. you had all these batteries load tested and they indicated bad cells or what ?

The dealer claimed a few things which I believe is BS after much research and speaking with others in the automotive field...

GM TECH SAID:

1) Your truck is black and therefore creates more heat under hood which kills batteries faster - I CALL BS. no facts to support this theory

2) 2 years is normal life of a battery for newer vehicles due to electrical loads - I CALL BS.... no facts to support this theory

3) You drive on bumpy roads and it causes the cells to clash in the batteries making them die faster.... Still BS likely, not 5 different batteries... I Do live on a dirt road, but so does 100 other people and thousands of others too for that matter... I could see one maybe, not 5.

The TECH did say he thought a parasitic draw from the onstar computer or BCM may be the cause of the dead batteries, but each time they tested they couldn't find anything (even keeping overnight)... but obviously something is occasionally killing battery OR not charging... the charging thing however (voltage drop issue that is) started within the last 6 months or so... seems there may be 2 seperate but combined issues..... I'm about ready to sell the damn thing and get something else; it's been great other than this...

[j cAT]

so what the problem is now going on would be the PCM is not commanding the alternator back on after a MPG programed action which would turn off the alternator.

I do not have a detailed diagram with these controls my guess is that the PCM has an external relay that feeds the alternator field voltage . this relay may be worn /burned contacts.

when replacing these batteries always have them load tested. place on a charger see if they are discharged or defective by not taking a charge.

on these newer trucks one thing I saw [actually many things] that I did not approve of is the firewall location of the battery.

[JimPratz]

Where do you think I could get more information on this external relay that feeds the alternator voltage?? Any ideas, I will try to talk to GM but am doubtful they will helpful, I've figured out more than they have so far...

Originally Posted by j cAT

so what the problem is now going on would be the PCM is not commanding the alternator back on after a MPG programed action which would turn off the alternator.

I do not have a detailed diagram with these controls my guess is that the PCM has an external relay that feeds the alternator field voltage . this relay may be worn /burned contacts.

when replacing these batteries always have them load tested. place on a charger see if they are discharged or defective by not taking a charge.

on these newer trucks one thing I saw [actually many things] that I did not approve of is the firewall location of the battery.

[j cAT]

Originally Posted by JimPratz

Where do you think I could get more information on this external relay that feeds the alternator voltage?? Any ideas, I will try to talk to GM but am doubtful they will helpful, I've figured out more than they have so far...

you could subscribe to ALLDATA. not all that expensive to get the specific diagrams for your vehicle,

I always buy the OEM helms manual with my new vehicle purchases. since I keep them for a decade or two I get my 120 USD worth for the complete info they contain.

I am guessing that it would be in the underhood fuse box.

[rhandwor]

http://www.2carpros.com/questions/ch...harge-question

[someday31]

Originally Posted by JimPratz

I wondered if anyone ever figured out an answer to this old this (new to the forums), my truck is doing the same exact thing (2008 Silverado, bought brand new, replaced alternator also with new GM AC DELCO (not rebuilt) and have gone thru literally 5 NEW BATTERIES... )... I've had the truck to the GM dealer 4 times for the issue and even over night and no answers, they have many excuses and like to say it's normal but it in fact IS NOT NORMAL, my truck used to always charge at around 13.6 to 14.2, I have NO after market accessories, only 66k miles on truck, any ideas...?? Everytime I have taken it to the GM dealer they say it checks out fine, same with Advanced Auto with their meters...

I did notice this however, when the voltage drops while dropping (goes down as low as 11.8v, but usually only goes down to 12.4v.... if it does this while driving, and I put in neutral, then restart truck it goes back up to 13.4v - 14.4v and stays there for quite a while, until next restart...

I'm in the process of replacing the 175AMP Megafuse but this is my last check I know of... (I am doubtful its the cause however)...

Thanks for everyone's help - Jim.

I never fully resolved my trucks issue. It still doesnt fully charge, and have killed batteries...I got so frustrated I just ignore it and dont worry about it. The truck runs and gets me where I want to go. The dealer is useless, and like you said you know more about this issue than them, just as I had/do through all my research.

[JimPratz]

I found this link for anyone with a GM factory service manuals 2007-2009 All Silverados/Sierras (LINK BELOW)


https://docs.google.com/uc?id=0B4loM...xport=download



It's pretty extensive, many factory PDF's of wiring, rebuilds, I think it's all factory information that dealers use on these vehicles, I'm going to look thru it and see if I can figure anything out.... if anyone has ideas where I'd start feel free to let me know: thanks for your help in advance ...

[j cAT]

Originally Posted by JimPratz

I found this link for anyone with a GM factory service manuals 2007-2009 All Silverados/Sierras (LINK BELOW)


https://docs.google.com/uc?id=0B4loM...xport=download



It's pretty extensive, many factory PDF's of wiring, rebuilds, I think it's all factory information that dealers use on these vehicles, I'm going to look thru it and see if I can figure anything out.... if anyone has ideas were I'd start feel free to let me know: thanks for your help in advance ...

well this looks more involved than I figured. I did some diging into the link you gave pretty good info this is what I found so far :

This vehicle is equipped with a regulated voltage control (RVC) system. This system turns off the
generator when it is not required in order to improve fuel economy. The generator will turn back on when additional voltage is required. This will cause the voltmeter to fluctuate between 12 and 14 volts as opposed to non-regulated systems which usually maintain a more consistent reading of 14 volts. This fluctuation with the RVC system is normal system operation and NO repairs should be attempted.


so GM says it is normal for the voltage to move between these readings. 12volts to 14 volts. I did not find the alternator control wiring control diagram yet.

[old_master]

In the voltage regulator electrical connector, (on the alternator) there are 2 wires. One in the "B" position, and one in the "C" position. You can install an additional wire in the "D" position and connect it to the terminal on the rear of the alternator. This will force the voltage regulator to sense battery voltage and regulate accordingly, just like the older systems without RVC. $10 in parts, 20 minutes time.

[JimPratz]

Originally Posted by j cAT

well this looks more involved than I figured. I did some diging into the link you gave pretty good info this is what I found so far :

This vehicle is equipped with a regulated voltage control (RVC) system. This system turns off the
generator when it is not required in order to improve fuel economy. The generator will turn back on when additional voltage is required. This will cause the voltmeter to fluctuate between 12 and 14 volts as opposed to non-regulated systems which usually maintain a more consistent reading of 14 volts. This fluctuation with the RVC system is normal system operation and NO repairs should be attempted.


so GM says it is normal for the voltage to move between these readings. 12volts to 14 volts. I did not find the alternator control wiring control diagram yet.

I too haven't found what I was looking for, and I totally understand about the RVC system, the problem is that when I got the truck, up until the last year; voltage always stayed around 13.4 to 14.6 or so; it never dropped below 13v, lately and more often it's been dropping down to 12.4, sometimes 11.8 even, and staying there even when driving 60mph with all accessories on; or stopping, tried many variations, .... the one thing I NOTICED.... if I just stopped wherever I was; and restarted the truck; it would many times go back up to the normal 13.8v to 14.2 (it really seems to have normally always stayed right around 14v (I'm OCD so I notice this sort of thing; maybe thats bad; but either way), maybe before it wasn't working correct and now it is, I dont' know... just doesn't seem right to be as low as 11.8 (which has happened more than once).. I did also btw change the 175AMP Mega Fuse, it worked perfect for 3 days, then 4th day, dropped back down to 12.xx Volts (I was hoping that was it)... Thank you to everyone for your help...

[old_master]

I would be more concerned about the battery going dead, than gaining a 1/2 mile per gallon in fuel mileage Add the circuit to the "D" terminal and forget about it.

[old_master]

Battery goes dead and you don't have to worry about gas mileage

[j cAT]

Originally Posted by JimPratz

I too haven't found what I was looking for, and I totally understand about the RVC system, the problem is that when I got the truck, up until the last year; voltage always stayed around 13.4 to 14.6 or so; it never dropped below 13v, lately and more often it's been dropping down to 12.4, sometimes 11.8 even, and staying there even when driving 60mph with all accessories on; or stopping, tried many variations, .... the one thing I NOTICED.... if I just stopped wherever I was; and restarted the truck; it would many times go back up to the normal 13.8v to 14.2 (it really seems to have normally always stayed right around 14v (I'm OCD so I notice this sort of thing; maybe thats bad; but either way), maybe before it wasn't working correct and now it is, I dont' know... just doesn't seem right to be as low as 11.8 (which has happened more than once).. I did also btw change the 175AMP Mega Fuse, it worked perfect for 3 days, then 4th day, dropped back down to 12.xx Volts (I was hoping that was it)... Thank you to everyone for your help...

when you start up the engine the battery gets drained. then the battery current sensor reports high current charge because of this, so then you get the normal voltage output from the alternator.

[JimPratz]

So, I have discovered something new... It appears the 2 fans on the radiator may be part of the problem.... the voltage output averages 13.4 - 14.4, but that's when you first start the truck; today, I noticed when the fans kicked on the voltage dropped all the way down to 11.2 volts; and didn't go back up over 12.4 to 12.8.... that's still too low.... so I restarted the truck, fans off again, voltage normal again... fans come on, voltage goes down to about 12.8 this time...and stays around 12.6 to 13.2 (which seems still low considering the AC is also running as well as headlights and truck is revved to about 1900 RPMS (changing RPMS did not alter the voltage; which you would think it might or should)...

The Voltage problem seems random however with the fans; sometimes does it; sometimes not so bad; ...

SO: question is; how can I further test the fans... maybe there's a high draw problem; they seem to move just fine, not seized that I can tell...

Anyone have an idea how many AMPS/VOLTS the 2 fans should be drawing??

Thanks again for your help

[j cAT]

Originally Posted by JimPratz

So, I have discovered something new... It appears the 2 fans on the radiator may be part of the problem.... the voltage output averages 13.4 - 14.4, but that's when you first start the truck; today, I noticed when the fans kicked on the voltage dropped all the way down to 11.2 volts; and didn't go back up over 12.4 to 12.8.... that's still too low.... so I restarted the truck, fans off again, voltage normal again... fans come on, voltage goes down to about 12.8 this time...and stays around 12.6 to 13.2 (which seems still low considering the AC is also running as well as headlights and truck is revved to about 1900 RPMS (changing RPMS did not alter the voltage; which you would think it might or should)...

The Voltage problem seems random however with the fans; sometimes does it; sometimes not so bad; ...

SO: question is; how can I further test the fans... maybe there's a high draw problem; they seem to move just fine, not seized that I can tell...

Anyone have an idea how many AMPS/VOLTS the 2 fans should be drawing??

Thanks again for your help

with the volts going below 12 volts this would be a failure according to the OEM service manual. it appears that it is not turning the alternator back on with high load. this could be that battery current sensor is messed up not reporting the correct current demand. with high demand the alternator should be a normal high output.

both fans use different amounts of current . I'm guessing about 25 amps for both .maybe 30 amps . 300-350 watts .