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Alternator shuts down after ~30 minutes of driving

Toggenburg

Full Member
Joined
Sep 26, 2021
Messages
24
2011 AV, last Friday, had to replace battery and alternator. Went to Home Depot at lunch hour, came back and engine would barely spin, but no start.
Guy there used porta jumper, car starts instantly. He leaves, and I pull out heading back to work (5 minutes away by expressway).
I get in traffic and notice the voltmeter is discharging, like 1/8" to the left of center.... not a normal sight.
Last mile or so, seemed that trans was having trouble shifting and I thought everything was going to shut down on me.
Made it to work, parked so the front end was out, because I might need battery recharging or maybe a tow...
Coworkers put cables on vehicle, battery would not budge, no start at all, voltmeter showed 9 or 10 vdc and would not charge.
Wife came and I bought an utoparts store rebuilt alternator and new AGM battery.
Swapped out and drove home no issue.
However; Monday, Tuesday and Wednesday, each time, driving home (45 minutes ~ 31 miles) at nearly the same time and place, the voltmeter gradually drops to the same spot as before.
Last night, Wednesday, on way home, traded alternator in for another at a different branch of same autoparts store.
Store tested and said, bad diode.
New one I then put in, had a noisy bearing and parts store had no other spare alternator.
Took tools with me to work today.
Lunchtime, back to original store where I purchased the items on previous Friday.
They tested and said electrically alternator was good, but bearing was bad.
Got yet another alternator from their shelf, it tested good and ran silent. Installed that one.
Ran fine back to work.
On way home though, at roughly 30 minutes from work, the voltmeter did the same thing!
I pulled onto a side street, turned off engine and then immediately restarted and voltmeter shoots up to 14.6 VDC.
Is there some electrical pathway in our AV's that the ECM or some other circuit can control the power to the alternator?
Forgot to mention, when the voltmeter shows discharge, I never get a red battery light to come on. I placed DMV on battery and it's 12.6 volts. Then immediately after restart, battery leads are showing 14.6 v, and on one of the previous alternators this week, I measured 14.9v spike.
What is going wrong and what do I need to do next (co workers say, it's just bad rebuilt ones and to go get my $ back and buy a brand new alternator....I don't think that the alternators themselves are the problem.
Is there some alternator shutdown relay on our cars?
Thoughts?
 
Last edited:
2011 AV, last Friday, had to replace battery and alternator. Went to Home Depot at lunch hour, came back and engine would barely spin, but no start.
Guy there used porta jumper, car starts instantly. He leaves, and I pull out heading back to work (5 minutes away by expressway).
I get in traffic and notice the voltmeter is discharging, like 1/8" to the left of center.... not a normal sight.
Last mile or so, seemed that trans was having trouble shifting and I thought everything was going to shut down on me.
Made it to work, parked so the front end was out, because I might need battery recharging or maybe a tow...
Coworkers put cables on vehicle, battery would not budge, no start at all, voltmeter showed 9 or 10 vdc and would not charge.
Wife came and I bought an utoparts store rebuilt alternator and new AGM battery.
Swapped out and drove home no issue.
However; Monday, Tuesday and Wednesday, each time, driving home (45 minutes ~ 31 miles) at nearly the same time and place, the voltmeter gradually drops to the same spot as before.
Last night, Wednesday, on way home, traded alternator in for another at a different branch of same autoparts store.
Store tested and said, bad diode.
New one I then put in, had a noisy bearing and parts store had no other spare alternator.
Took tools with me to work today.
Lunchtime, back to original store where I purchased the items on previous Friday.
They tested and said electrically alternator was good, but bearing was bad.
Got yet another alternator from their shelf, it tested good and ran silent. Installed that one.
Ran fine back to work.
On way home though, at roughly 30 minutes from work, the voltmeter did the same thing!
I pulled onto a side street, turned off engine and then immediately restarted and voltmeter shoots up to 14.6 VDC.
Is there some electrical pathway in our AV's that the ECM or some other circuit can control the power to the alternator?
Forgot to mention, when the voltmeter shows discharge, I never get a red battery light to come on. I placed DMV on battery and it's 12.6 volts. Then immediately after restart, battery leads are showing 14.6 v, and on one of the previous alternators this week, I measured 14.9v spike.
What is going wrong and what do I need to do next (co workers say, it's just bad rebuilt ones and to go get my $ back and buy a brand new alternator....I don't think that the alternators themselves are the problem.
Is there some alternator shutdown relay on our cars?
Thoughts?
Is there some alternator shutdown relay on our cars? Sort of, called the EPM system
This article may help you.


In the interest of alleged fuel economy GM changed the (simple and easy to diagnose) way vehicle batteries are charged in 2007. The old days of a constant float charge are gone. Basically the computer decides there are "times" when the alternator's output is intentionally lowered (thus slightly less engine load). In reality the old days of constant float charge did contribute to reduced battery life, thus if the "computer control" works correctly battery life may be enhanced in addition to the hypothetical fuel economy benefit.
 
2011 AV, last Friday, had to replace battery and alternator. Went to Home Depot at lunch hour, came back and engine would barely spin, but no start.
Guy there used porta jumper, car starts instantly. He leaves, and I pull out heading back to work (5 minutes away by expressway).
I get in traffic and notice the voltmeter is discharging, like 1/8" to the left of center.... not a normal sight.
Last mile or so, seemed that trans was having trouble shifting and I thought everything was going to shut down on me.
Made it to work, parked so the front end was out, because I might need battery recharging or maybe a tow...
Coworkers put cables on vehicle, battery would not budge, no start at all, voltmeter showed 9 or 10 vdc and would not charge.
Wife came and I bought an utoparts store rebuilt alternator and new AGM battery.
Swapped out and drove home no issue.
However; Monday, Tuesday and Wednesday, each time, driving home (45 minutes ~ 31 miles) at nearly the same time and place, the voltmeter gradually drops to the same spot as before.
Last night, Wednesday, on way home, traded alternator in for another at a different branch of same autoparts store.
Store tested and said, bad diode.
New one I then put in, had a noisy bearing and parts store had no other spare alternator.
Took tools with me to work today.
Lunchtime, back to original store where I purchased the items on previous Friday.
They tested and said electrically alternator was good, but bearing was bad.
Got yet another alternator from their shelf, it tested good and ran silent. Installed that one.
Ran fine back to work.
On way home though, at roughly 30 minutes from work, the voltmeter did the same thing!
I pulled onto a side street, turned off engine and then immediately restarted and voltmeter shoots up to 14.6 VDC.
Is there some electrical pathway in our AV's that the ECM or some other circuit can control the power to the alternator?
Forgot to mention, when the voltmeter shows discharge, I never get a red battery light to come on. I placed DMV on battery and it's 12.6 volts. Then immediately after restart, battery leads are showing 14.6 v, and on one of the previous alternators this week, I measured 14.9v spike.
What is going wrong and what do I need to do next (co workers say, it's just bad rebuilt ones and to go get my $ back and buy a brand new alternator....I don't think that the alternators themselves are the problem.
Is there some alternator shutdown relay on our cars?
Thoughts?
It only charges when the voltage is needed, it is measured through the computer and if the battery goes below 12 volts the computer kicks in the alternator, it's suppose to be part of the fuel management system, I have a 2010 that I thought was also bad, but after reading about it, it's normal, mine only charges when I have on the A/C for a while or when I use the headlights and directly after the initial start up. Just let it do its thing and you'll be fine.
 
Well, thank you, that explains it all.
OK, I did need a battery, and guessing the alternator I had was original to the car (233K) this 3rd alt works fine then.
Learn summat new every day !
 
before replacing battery:
Remove from truck and trickle charge.
Then bring to local autoparts store where they can load test it to ensure it is bad.

Might save ya $200 as batteries got expensive.
 
Thanks, I know to do all that, however, older battery and I was stuck at work, 33 miles from home.
Could not trickle charge, in fact, no one at work had a charger of any sorts, no porta jump box either.
and, with the only set of jumper cables we could find.....hooked to the battery for 15 minutes, the battery would not take any charge at all.
 
You could take your alternator to a proper alternator rebuilding shop, and have them install an internal voltage regulator. (if possible to do on GM alternators...I'm not sure)
Years ago, our shop used to do that with certain Chrysler products where the computer controlled charging system had failed.
Alternator would be reinstalled the same way, but there was one spade connector in the alternator harness that you would bend out of the way and leave unbolted from the alternator - essentially bypassing that circuit, and allowing the internal regulator inside the alternator to do the job. I suppose you could get that done if you are fed up of how the charging system behaves.
 
I'm not fed up with how the GM charging system works, I was just completely unaware of how it worked and how different it is from all my other vehicles which are 2004 and older. Now that I had it explained I am fine with the gauge going below midpoint.
Thanks all for showing me what GM had done since 2097.
 
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