Alternator being flakey?

seanpooh

Original poster
Member
Jan 24, 2012
461
Hey guys, I would love to hear some of your inputs on this.

So yesterday I auto started my Envoy (which hasn't been driven for 3 days nor working under the hood since I changed the battery 5K miles ago/2 months ago) and it shut off in ~5 minutes. I went inside and started it manually and all went fine until the DIC stated that my battery was not charging and that red battery light came on. In fear of losing power and being in limp mode, I didn't drive it that day.

So of course first thing came to mind was to Google it. I've read some threads here and on the OS but none fits my situation.

I have a multi meter and got some readings.
When off and main terminal disconnected from battery, I have a reading of 12.53V.
When started and at idle with all accessories, headlights, and cluster lights off, I have a reading of 11.98V.
At idle with cluster lights on max, dome lights and headlights, I have a reading of 11.72V.
Then when I take everything off again I get the original reading at idle of 11.98V.
Finally when I shut the engine off and measure the battery, it's back up to 12.32V.

My instrument cluster for the battery reads at the bolder marker between 9 and 14V when at idle.
I did have my girlfriend step on the gas while I read the battery and it was a constant 11.99V.
The battery is from Sam's Club and it's the Duracell brand.

So my guess is the alternator is not generating enough output? The battery is accepting the charge since the voltage does go back up to the 12V range but it doesn't go past the 12-12.6V range. I don't suspect it being a defect unless it has a bad cell that isn't taking a charge.

I checked all connections, wiggled and fiddled with them and all seems secure and not corroded or broken. The only electrical work I've done is the HIDs and that was since the summer. There is no flickering or dimming. I checked all the fuses under the hood (#10,22,23,28) and #47 in the rear under seat. Belt is tight and tension arm isn't wiggling.

I will be going off to Advance Auto for a load test but I just wanted to share to you guys first. Let me know what you think.
 

Matt

Member
Dec 2, 2011
4,029
Double check your battery connections for tightness...don't use your fingers, use a wrench to make sure. I had a similar problem and found that my positive terminal was loose. I checked it using my fingers and it was tight but when I put a wrench on it it felt loose...tightened it up, problem solved.

Failing that, get the alt tested.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
The battery voltage is lower when the engine is running because of the current draw of running the PCM, injectors, etc. When you remove that load when the engine's off, the battery's true voltage shows up. Your alternator might as well not be there. It could be dead, or the control wire from the PCM to the alternator could be bad (less likely).
 

seanpooh

Original poster
Member
Jan 24, 2012
461
Yeah, I think that's what I have to do and I've researched many How To Do articles and one youtube video to get the job done. I will be doing my powersteering also and O2 sensor and spark plugs since I'm getting 11mpg @ 70mph, :hissyfit: Maybe the u-joint too...

Yesterday I drove about 30 miles on the bad alternator to have a load test done to find out if it was either the battery or my alternator and also to run some errands. Not a good idea... I got to my University to drop off paperwork. The guage showed 11V still. Shut it off, drop papers and then got back in a started it up. Now the 11V was heading to 9V :no:
Good thing Interstate battery was not to far away. While driving, the seatbelt and airbag lights started to blink, then the cluster gauge came off. I knew it was the safety feature to save as much battery to limp. But I got there.

The Interstate battery guys were really nice and gave me a loaner battery to make it home. Good guys working there. Called up my local junk yard and they have the LWB alternator with 75K miles for $50 so I think it's a good deal. I won't get it until Wednesday though. But in the mean time I'll get everything out to prepare.

I will let you guys know if it was the alternator (it must be). Thanks guys.
 

gmcman

Member
Dec 12, 2011
4,656
I had the same issue and I wiggled this wire around while it was running and it was clearly a bad connection. Worth a try.
 

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seanpooh

Original poster
Member
Jan 24, 2012
461
I did no with no avail. I did read a thread about a guy tracing those two wires back to the main wire loom and it was not getting a good connection. He had to splice and re solder them together. I will check these wires out first before removing the alternator.

I don't see why my alternator would go bad all of a sudden on a not so cold day. But then it is all electrical and anything can go wrong. The wire wiggling is worth a try.
 

seanpooh

Original poster
Member
Jan 24, 2012
461
Alright guys, so I changed out the alternator but before thightening the bottom bolt I decided to start her up and see what the deal was.

I attached the battery and put the belt back on and turn the key and :wootwoot: the voltage gauge was back up to 14V.

It was a wonderful feeling to see that happen. Still don't know what's wrong with the old one but I'll be keeping it instead of getting back the $10 core fee.

Along with changing the alternator, I did change my power steering pump, O2 sensor, ECT and spark plugs. I never did the ECT since I didn't remove the alternator when I did the thermostat.

I must say for references, taking out the alternator is a MUST if you want to change the thermostat, ECT and motor mount. You have soo much room to work with and makes it much easier to fit your hands and tools.

So in the end, the alternator was bad. I appreciate all your guys suggestions and help. I appreciate it all.
 

meerschm

Member
Aug 26, 2012
1,079
seanpooh said:
Alright guys, so I changed out the alternator but before thightening the bottom bolt I decided to start her up and see what the deal was.

I attached the battery and put the belt back on and turn the key and :wootwoot: the voltage gauge was back up to 14V.

It was a wonderful feeling to see that happen. Still don't know what's wrong with the old one but I'll be keeping it instead of getting back the $10 core fee.

Along with changing the alternator, I did change my power steering pump, O2 sensor, ECT and spark plugs. I never did the ECT since I didn't remove the alternator when I did the thermostat.

I must say for references, taking out the alternator is a MUST if you want to change the thermostat, ECT and motor mount. You have soo much room to work with and makes it much easier to fit your hands and tools.

So in the end, the alternator was bad. I appreciate all your guys suggestions and help. I appreciate it all.

Why keep the bad one? do you plan to take apart, repair?
 

seanpooh

Original poster
Member
Jan 24, 2012
461
My dad told me to keep it. I guess he will find a guy to fix it if it could be fixed. I guess a broken altenator is better than $10 back. Or he will just take it apart like everything else then throw it away :rotfl:
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
There are alternator rebuilding shops in almost every medium/large city.

Or he could believe in the axiom that if you take something apart and put it back together enough times, sooner or later you'll have enough parts to make TWO of 'em!
 

meerschm

Member
Aug 26, 2012
1,079
since the first one lasted ten years, you should have plenty of time to figure out what was wrong. There are also plenty of u tube videos and sites to help if you (or your dad) want to play with it. might make a nice hobby item or a spare part.
 

pbone

Member
Dec 27, 2012
2
I am having a similar issue with my envoy, however I would sometimes get volatge (14.1V) and other times not and the bat light would come on and say not charging. I have a new battery and changed the alternator but am still getting the intermitent voltage. Not sure how I should check to see if my plug or wirrin to the PCM is bad or if the PCM is sending the correct signal.

Any thoughts?
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Welcome. Check the condition of the two wire plug in the earlier post #6. You would need a meter looking at the control wire at the exact moment you have the problem. How often does it happen, and do you have a meter and electrical troubleshooting experience?
 

pbone

Member
Dec 27, 2012
2
the roadie said:
Welcome. Check the condition of the two wire plug in the earlier post #6. You would need a meter looking at the control wire at the exact moment you have the problem. How often does it happen, and do you have a meter and electrical troubleshooting experience?

Thanks glad to have joined the group!

I do have a meter and electrical experience. Seems to be happening every other day or so. The truck died again yesterday after the new alternator was in and I limped it into the garage and charged it up after jumping it. When I jumped it I played with the connection and wire a bit and the light was not on while I drove it into the garage.

What voltage would the PCM be sending to the alternator in order to have the alternaotr operate? Also where does the signal come from to indicate the battery is not charging?
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Funny thing - I've never looked at that signal to see if it needs a high or a low to turn on the alternator. The battery light on the dash is illuminated, as are most warning lights, by a digital data message from the PCM.
 

seanpooh

Original poster
Member
Jan 24, 2012
461
I was looking at the service manual that we could download on this site and I believe there is a test to determine if the two wires and PCM are functioning correctly with the alternator. It's under Engine Electrical and I can't remember if you needed a TechII to send commands...

EDIT: Just skimmed through it and yeah, you do need a TechII to send commands for the generator to turn on and off and probe the terminal and look at the readings. Then the fixes are to check wiring harness, replace if needed and/or replace PCM. It is a helpful book though, but they tell you that the first step in removing the alternator is to disconnect the grounding off the alternator... :book: If you took the engine out first, then yeah.
 

Tofer76

Member
Dec 8, 2011
148
seanpooh said:
Yeah, I think that's what I have to do and I've researched many How To Do articles and one youtube video to get the job done. I will be doing my powersteering also and O2 sensor and spark plugs since I'm getting 11mpg @ 70mph, :hissyfit: Maybe the u-joint too...

Yesterday I drove about 30 miles on the bad alternator to have a load test done to find out if it was either the battery or my alternator and also to run some errands. Not a good idea... I got to my University to drop off paperwork. The guage showed 11V still. Shut it off, drop papers and then got back in a started it up. Now the 11V was heading to 9V :no:
Good thing Interstate battery was not to far away. While driving, the seatbelt and airbag lights started to blink, then the cluster gauge came off. I knew it was the safety feature to save as much battery to limp. But I got there.

The Interstate battery guys were really nice and gave me a loaner battery to make it home. Good guys working there. Called up my local junk yard and they have the LWB alternator with 75K miles for $50 so I think it's a good deal. I won't get it until Wednesday though. But in the mean time I'll get everything out to prepare.

I will let you guys know if it was the alternator (it must be). Thanks guys.

there is no difference in the alt for swb or lwb , they all are the same . however the belt is diff

http://gmtnation.com/f25/tensioner-hitting-crank-pulley-5382/

post 8 9 and 10
 

bspurloc

Member
Dec 27, 2012
295
seanpooh said:
I was looking at the service manual that we could download on this site and I believe there is a test to determine if the two wires and PCM are functioning correctly with the alternator. It's under Engine Electrical and I can't remember if you needed a TechII to send commands...

EDIT: Just skimmed through it and yeah, you do need a TechII to send commands for the generator to turn on and off and probe the terminal and look at the readings. Then the fixes are to check wiring harness, replace if needed and/or replace PCM. It is a helpful book though, but they tell you that the first step in removing the alternator is to disconnect the grounding off the alternator... :book: If you took the engine out first, then yeah.

Just curious,
How many miles on your '02? My daughters alternator brushes were totally gone at 150k. When the brushes hit end of life you get good voltage bad voltage and eventually total failure due to the brushes totally wearing out making it impossible to create a voltage anymore. Replacing it was pretty fast with electric fans as you have mega hand room :wink:
 

seanpooh

Original poster
Member
Jan 24, 2012
461
The exact miles when I changed the alternator was 159,118 miles. I didn't have the intermittent charging and not charging as you describe. Just one morning I started it and the DIC stated that the battery was not charging.

I should of did some research about how alternators work...:undecided: time to search Google.
 

bspurloc

Member
Dec 27, 2012
295
seanpooh said:
The exact miles when I changed the alternator was 159,118 miles. I didn't have the intermittent charging and not charging as you describe. Just one morning I started it and the DIC stated that the battery was not charging.

I should of did some research about how alternators work...:undecided: time to search Google.

Interesting :smile: I think the brushes in a lot of alternators last around 150,000. I think they were spent in my '87 Tbird at 150k also. Hers only did the bad good thing for 2 days max. She started complaining about it then one night she told me the car said it wasnt charging anymore so I went directly to the car store for an alternator.
 

mcsteven

Member
Apr 18, 2012
6,584
I wasn't sure if I should reply here or start a new thread, so I put it here first.

I was getting a lot of days with no start. Quick jump, fired right up. Finally I noticed that, sometimes, if I'm sitting at idle (or stopped in drive, foot on brake) with the blower motor running, the lights will dim and the voltmeter drops. Bring the RPMs up to about 600 or 800, and the voltmeter returns to center. Since I've noticed this and revved or gone to idle and revved, I've not had any issues starting it.

When I would jump it, and be running / driving for 20 minutes, it was all set. Fired up again without issue.

I have no extra electrical items except for charging my phone (only while the engine is running). I sometimes listen to the radio after shutting off the car until it turns off automatically.

2006, 4.2L I-6 SLT (non XL).

As a side note, is there a difference between the alternators for the std and XL versions of our trucks? I'm hoping to add some more lighting and an AC inverter, so of course more is better.

If this is a voltage regulator, is that built into the alternator or a separate unit?

Thanks for all your help folks.

Marc
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
1) No start due to a discharged battery is often caused by a parasitic drain. Or an aged battery. Is this still happening?

2) Low idle RPM that sometimes stalls the engine out, especially after a discharged battery incident and with the AC compressor cycling on and off, is a known problem of a dirty throttle body. We have an Article on how to clean it.

3) The alternators on our vehicles are all alike at 150A. Some parts stores have software that asks the question if we have a 140-145 A unit, but all the vehicles use 150A. There is a legitimate question if you have a shortie or long wheelbase in terms of the right fan belt to get, but that's related to the power steering pump pulley size, not the alternator.

4) The regulator is built into the alternator. There are two control wires going from the alternator to the PCM. One to tell the PCM how hard the alternator is working, and the other one to allow the PCM to suppress the alternator from turning on for a few seconds after a cold start. No external voltage control.
 

mcsteven

Member
Apr 18, 2012
6,584
the roadie said:
1) No start due to a discharged battery is often caused by a parasitic drain. Or an aged battery. Is this still happening?

2) Low idle RPM that sometimes stalls the engine out, especially after a discharged battery incident and with the AC compressor cycling on and off, is a known problem of a dirty throttle body. We have an Article on how to clean it.

3) The alternators on our vehicles are all alike at 150A. Some parts stores have software that asks the question if we have a 140-145 A unit, but all the vehicles use 150A. There is a legitimate question if you have a shortie or long wheelbase in terms of the right fan belt to get, but that's related to the power steering pump pulley size, not the alternator.

4) The regulator is built into the alternator. There are two control wires going from the alternator to the PCM. One to tell the PCM how hard the alternator is working, and the other one to allow the PCM to suppress the alternator from turning on for a few seconds after a cold start. No external voltage control.

I don't think it's a parasitic drain. I've been gone for a week or more and it starts right up. Possibly aged battery, but in the last 2 or 3 weeks, after I noticed the dimming lights when the blower was on (and shut off the blower or gassed and held at 600-800 RPM) I haven't had an issue. But I do notice the lights dimming and voltmeter dropping so I take measures to correct or counter.

2.) It's never stalled like that. I've never had it stall except when it ran out of gas.

3.) Cool. So we have different belts. Good to know.

4.) So if it's a regulator we're SOL and have to replace the alternator?

The issue is when it's parked, or stopped, and the blower is on, I often (not always) see dimmed lights, hear the blower slow, and see the voltmeter drop until I take measures.

Thanks for jumping on this so quick Roadie. I appreciate any and all help here.
 

Tofer76

Member
Dec 8, 2011
148
X2 on what roadie said! For your future ref. Short wheel base=long belt. Long WB=shorter belt. All have a 150a alt and i think there is a high amp alt avail but its perty expensive if i recall. Get a lifetime warranty on ur new one cuz if add things it may go again. Ps. Want a black billit grille for ur voy? Pm me lol
 

JerryIrons

Member
Dec 20, 2011
434
bspurloc said:
Just curious,
How many miles on your '02? My daughters alternator brushes were totally gone at 150k. When the brushes hit end of life you get good voltage bad voltage and eventually total failure due to the brushes totally wearing out making it impossible to create a voltage anymore. Replacing it was pretty fast with electric fans as you have mega hand room :wink:
I realize that I am posting to something over a year ago, but just wanted to add my experience to a similar thread. I head out to work this morning, and notice my battery indicator light is on. (I've never seen that before) Then I step up the rpms to about 2000, and the light goes off. Shortly after the indicator light pops back on again. So I drive back home, and get the meter out. I have my wife sit in the car and give it gas up to 2000 and let it idle back down while I'm checking voltage at the battery. Just like the poster above mentioned, voltage was kind of random for no real reason, it would be up at 14 volts, then drop down to below 10. Rpm's didn't seem to matter. Basically acting like the brushes were almost failing but not quite dead yet. I did try jiggling the connector around a little with no help, the wires looked fine.

A trip to napa for a new alternator, and everything is fixed and works great. The original alternator had 190,000 miles on it, so I can't complain. Thought I'd post this in case it helps anyone with similar conditions. I've had alternators fail on other cars, but each of those times it was a total failure.
 

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