[SOLVED] crazy problem with alternator [Archive] - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

: [SOLVED] crazy problem with alternator


jimc
03-05-2011, 10:16 AM
Read this site every time I have issues with my 04 Trailblazer (bought new now has 150k miles) or my 02 envoy (bought new now has 160k miles) and the info here has helped me do everything necessary up until now. You folks are amazing.

I'm now having a problem that I cannot find info to resolve. My wife called with the battery light on in the 2002 envoy. Told her what to expect and to drive straight home. She almost made it when the battery died. Charged it and drove home on the battery alone. Belts and idler pulley are fine. Took out the alt and took it to a Napa store. It tested bad. Put in a new one, charged battery and started it. Still no charge. Voltmeter reads 11.9volts at the battery. The battery was 3 years old and when charging it the meter on the charger jumped around a bit oddly, so I put in a brand new battery, removed and cleaned the terminals and all the grounds I could find, including the big 3 discussed on this site. Exchanged the new alternator (which tested bad at napa, although I am not confident they knew how to use the test unit) for another one. Installed the 2nd new alternator and the new battery, charged it and fired up the car. Still no charge. I have continuity from the alt to the postive terminal, and at all ground points. The only thing left that I can think of is that the small plug and/or wires to the back of the alternator that powers the electromagnets is bad, but I have no idea how to test them.

Anybody have any ideas? I am stuck.

cgallo
03-05-2011, 10:47 AM
Read this site every time I have issues with my 04 Trailblazer (bought new now has 150k miles) or my 02 envoy (bought new now has 160k miles) and the info here has helped me do everything necessary up until now. You folks are amazing.

I'm now having a problem that I cannot find info to resolve. My wife called with the battery light on in the 2002 envoy. Told her what to expect and to drive straight home. She almost made it when the battery died. Charged it and drove home on the battery alone. Belts and idler pulley are fine. Took out the alt and took it to a Napa store. It tested bad. Put in a new one, charged battery and started it. Still no charge. Voltmeter reads 11.9volts at the battery. The battery was 3 years old and when charging it the meter on the charger jumped around a bit oddly, so I put in a brand new battery, removed and cleaned the terminals and all the grounds I could find, including the big 3 discussed on this site. Exchanged the new alternator (which tested bad at napa, although I am not confident they knew how to use the test unit) for another one. Installed the 2nd new alternator and the new battery, charged it and fired up the car. Still no charge. I have continuity from the alt to the postive terminal, and at all ground points. The only thing left that I can think of is that the small plug and/or wires to the back of the alternator that powers the electromagnets is bad, but I have no idea how to test them.

Anybody have any ideas? I am stuck.

Please review continuity between PCM Conncetor 2 pin 51 cable gray and small plug in the alternator, cable gray, if you have continuity, maybe you could have PCM problems.:yes:

jimc
03-05-2011, 02:15 PM
thanks-I'll check and let you know.

jimc
03-05-2011, 04:03 PM
OK, I checked the continuity between the altermator plug gray wire and pin 51 on the pcm plug 2, and there is perfect continuity.

So, should I assume that means the pcm is not sending current to the alternator to power the coils? If so, do these pcms just go bad, or do you think I need to get it reflashed?

the roadie
03-05-2011, 04:29 PM
I would suspect the other wire first, the ON command wire. The alternator can be suppressed on a cold start by the PCM, to allow the engine idle to stabilize for a few seconds before throwing the additional load of the alternator trying to recharge a cold, depleted battery. The field PWM signal is from the alternator TO the PCM, so the PCM knows how hard the alternator is grunting and enabling the PCM to shed load if there's too much demand.

jimc
03-05-2011, 05:11 PM
thanks- I'll check that out in the morning. I'm a little uncertain if the diagram is telling me the 2nd pin on connector 3, or the 15th pin on connector 2?

Also, I knew connector 2 had to be the center one of three. How do I tell which is one and which is three, by the color?

jimc
03-05-2011, 07:12 PM
looked a little closer at the schematic, and I figured out that it is #2 on C3, still need to work out which plug is c3.

cgallo
03-05-2011, 08:24 PM
looked a little closer at the schematic, and I figured out that it is #2 on C3, still need to work out which plug is c3.

The schematics is for a 4.2 l and for 5.3 L

For 4.2 L Field Duty CYcle is C2 pin 51 Gray
Generator On Sig is C3 pin 2 Red.

Ok, you can measure a voltage in C2 pin 51 Field Duty when the engine is runnig, this signal tells to the PCM how is the charge in the alternator in order to the PCM, adjust idle acceleration, and as Roadie said, the other signal, C3 pin 2 , Generator ON, is who turn on /off the Rotor when the PCM indicates, you must measure 12v when the car is runnig, if not, check continuity between C3 pin2 and the small plug alternator cable red, also check, connector adjustment.:tiphat

Please, sorry for my English.

A Friend from Medellin, Colombia

jimc
03-06-2011, 11:09 AM
Thanks Cgalla and Roadie,

We may be getting somewhere. There is no continuity between c3 pin 2 and the red plug wire at the alternator.

Just to be sure I did this right- It looks to me like plug/connector 3 is the white one toward the front of the car. A red wire goes to pin 2. That pin has no continuity to the alternator.

So my guess is a bad connection from wire to pin in the alternator plug. Any suggestions or additional comments before I cut wires?

Frozen in Ohio.

bromanjr
03-06-2011, 11:15 AM
Yes, I agree, Because the Alternator has been recently worked on, I would suspect the wire is broken at or near the Plug going into the Alternator.

It would be best to remove the terminal from the alternator connector first. Either way you may be able to see that the wire may be too flexible at some point (broken inside the insulation).

Probing the wire at various points with a pin and checking continuity will tell you where it is bad.

jimc
03-06-2011, 11:20 AM
thanks- I'll try that next, although I may not have time for a couple days. Have to do some travelling.

cgallo
03-06-2011, 01:57 PM
I think, the problem is red cable broken near to the alternator connector, you can test as the other member said , pricking the red cable far of the conector and review continuity to the connector of PCM, please let us to know the solution.


Cesar Gallo

jimc
03-12-2011, 12:13 PM
:thxthanks CG and Roadie.

The red wire was seperated inside the insulation just outside the plug. Ordered a new one, popped it in, and we are off to the races.

Never would have found it without your help.

johnc441
03-04-2012, 11:17 PM
:thxthanks CG and Roadie.

The red wire was seperated inside the insulation just outside the plug. Ordered a new one, popped it in, and we are off to the races.

Never would have found it without your help.

hey jimc, do you have the part number for this? i saw the connector on the rockauto site, but i wasn't sure if that would include the wires as well. :)


3-5-12 6:57 PM ET - i was able to fine the connector, made by AC Delco, part # PT1383 .and confirmed with Rock Auto that this "connector" is a pig-tail connector (meaning it has the wires coming out of it. Note: PT1383 fits the '03 Envoy SLE, not sure what the part # is for the other model/years

wiredawg
07-20-2015, 09:44 PM
OK, I checked the continuity between the altermator plug gray wire and pin 51 on the pcm plug 2, and there is perfect continuity.

So, should I assume that means the pcm is not sending current to the alternator to power the coils? If so, do these pcms just go bad, or do you think I need to get it reflashed?

Hello JimC, can you are someone here explain/clarify how to access the cabling plug to find "pin 51" on the pcm plug. I used a 8MM socket to detach the plug from the PCM block. But I did not understand how one determine the numerical value to find "pin51".

wiredawg
07-20-2015, 09:48 PM
OK, I checked the continuity between the altermator plug gray wire and pin 51 on the pcm plug 2, and there is perfect continuity.

So, should I assume that means the pcm is not sending current to the alternator to power the coils? If so, do these pcms just go bad, or do you think I need to get it reflashed?

:thxthanks CG and Roadie.

The red wire was seperated inside the insulation just outside the plug. Ordered a new one, popped it in, and we are off to the races.

Never would have found it without your help.

Also, when you say "popped it in", did you splice the new harness wiring into the old wiring or did you connect the new wiring harness into the PCM plug itself and if so, how did you open the PCM plug/connector?

cgallo
07-20-2015, 11:45 PM
Please Check the attachment and let me Know

cgallo
07-20-2015, 11:54 PM
Check it the new attach, I did a Mistake en C3, is Pin 2 . I mark pin 3. The correct is C3 pin 2.

Attachment ok now

wiredawg
07-21-2015, 02:12 AM
Thank You CGallo, that makes much more sense to me. And since I have your attention: :)

My question is regarding the two control wires (alternator plug) . I read that one should have a constant 12VDC or so(red lead/right side with clip down) and the other pin (grey wire) should only see a reading when the key is in the "on" position. In my case, I checked the pins and I have 12.66VDC on the red-lead-pin and 12.56VDC on the other grey-lead-pin while my vehicle is in the "off" position (no key). Is this a malfunction??? Basically, I cannot get my my charging system to function properly after getting a "battery light" indication on dash along the the message "battery not charging". And the battery is not registering 14.5VDC while running, just the 12.6 or so. Also, not 100% sure about this fact will need to verify tomorrow. But, was getting very loud squealing via serpentine belt and thought this was a belt alignment problem shot some water on it, just to narrow down the squeal to no avail, no change in squeal at all. For some reason I decided to remove my 2-wire plug from the alternator and about 15 sec later the squealing stop completely gone. Will have to test this theory to be sure this is the cause and affect of the squeal. Have you ever heard of such a symptom. Also, had this "new" alternator tested 3 times and it was report as good. Though, "squeal not fully verified within alternator". So my next logical guess is the wiring harness and the 12VDC constant on both pins...at this point I'm stuck. Will check for basic continuity with your diagram, wondering if I got a short somewhere that's causing the constant 12VDC on grey-wire-pin. But, this is driving me nuts. Should have been a simple replace and go...LOL

cgallo
07-21-2015, 09:56 AM
1. Measurements should do with the bonding to the alternator connector, not in the air, since this uses a clip on the back of the conecror to see the voltages of the two wires, red and gray.
2. When the alternator is charging should be a varying voltage at terminal L and and if you put loads such as ventilation, highlights, should vary the voltage at terminal and L
3. It is important to check for shorts to 12th with other cables in those two signals.

Let me Know the advancees.

wiredawg
07-22-2015, 05:53 PM
1. Measurements should do with the bonding to the alternator connector, not in the air, since this uses a clip on the back of the conecror to see the voltages of the two wires, red and gray.
2. When the alternator is charging should be a varying voltage at terminal L and and if you put loads such as ventilation, highlights, should vary the voltage at terminal and L
3. It is important to check for shorts to 12th with other cables in those two signals.

Let me Know the advancees.

CGallo thank for taking the time to respond. Let me summarize my issue:
Main Problem>charging system not working ("battery light" on & "battery not charging" on DIC.

Fix actions>Have old alternator and Battery tested at Autozone. Alt fails (no surprise, never been replaced). Battery overheating (again, no surprise no name battery about 4 yrs old. Purchased new alt &bat, additional item needed was the 2-wire harness plug, one wire broke off at connector while unplugging it from alternator.

-Install items like clockwork...no real issues, other than pain in the butt bottom bolt to secure alternator.
--Turn on engine: loud squeal, sounds like mis-aligned serpentine belt.
--Dash still indicates "no battery charge", check meter across "pos & neg" posts, reads 12.6...not good...Stop engine
--Metered across "alt case housing" and "positive battery post"...reads 12.66vdc and also check with power-on lamp tester...lights up brightly.
--Removed new Alternator had it tested at 3 different place (2 autozones & an advanced auto) it test fine.
--Note: today, I figured out the squealing is coming from the new alternator.
--Re-installed alt and started it squeals and doesn't stop squealing...turned-off
--Removed 2-wire plug, started vehicle; slight squeal for about 3 sec then normal...turned off.
--Returned plug...started vehicle...squeal again...this time removed plug while vehicle is running, squeal gone. So, I know what is squealing, just don't know why?

-This brings me back to the power questions regarding the 2-wire harness. The only anomaly I can find in researching alternator issues. Everything else seems spot on for the alternator to function correctly.?.?.?
--So, In the key-off/no key position, I have a constant 12+VDC on both pins when measured against the positive post on the battery:
--Multi-meter "red-lead" to "positive post" of battery & multi-meter "blk-lead" to pin of red-wire) 12.62vdc This is okay, constant on...right?
--(Multi-meter "red-lead" to "positive post" of battery & multi-meter "blk-lead to pin of "grey-wire) 12.72vdc There should "NOT" be voltage on this wire/lead in no-key position...right?

-So, started pulling back the leads attached to the harness and so far I can't find this mystery DC voltage. I have not yet pulled off the PCM plug, but at this point not sure what good this will do me. Continuity does not seem to be the problem, but this stray voltage is...I guess the grey wire could be shorting with the red wire somewhere, will continue to look and see what I can figure out. Just thought I update here and maybe someone may have run into this issue. Thanks again for the diagram.

wiredawg
07-22-2015, 09:39 PM
CGallo thank for taking the time to respond. Let me summarize my issue:
Main Problem>charging system not working ("battery light" on & "battery not charging" on DIC.

Fix actions>Have old alternator and Battery tested at Autozone. Alt fails (no surprise, never been replaced). Battery overheating (again, no surprise no name battery about 4 yrs old. Purchased new alt &bat, additional item needed was the 2-wire harness plug, one wire broke off at connector while unplugging it from alternator.

-Install items like clockwork...no real issues, other than pain in the butt bottom bolt to secure alternator.
--Turn on engine: loud squeal, sounds like mis-aligned serpentine belt.
--Dash still indicates "no battery charge", check meter across "pos & neg" posts, reads 12.6...not good...Stop engine
--Metered across "alt case housing" and "positive battery post"...reads 12.66vdc and also check with power-on lamp tester...lights up brightly.
--Removed new Alternator had it tested at 3 different place (2 autozones & an advanced auto) it test fine.
--Note: today, I figured out the squealing is coming from the new alternator.
--Re-installed alt and started it squeals and doesn't stop squealing...turned-off
--Removed 2-wire plug, started vehicle; slight squeal for about 3 sec then normal...turned off.
--Returned plug...started vehicle...squeal again...this time removed plug while vehicle is running, squeal gone. So, I know what is squealing, just don't know why?

-This brings me back to the power questions regarding the 2-wire harness. The only anomaly I can find in researching alternator issues. Everything else seems spot on for the alternator to function correctly.?.?.?
--So, In the key-off/no key position, I have a constant 12+VDC on both pins when measured against the positive post on the battery:
--Multi-meter "red-lead" to "positive post" of battery & multi-meter "blk-lead" to pin of red-wire) 12.62vdc This is okay, constant on...right?
--(Multi-meter "red-lead" to "positive post" of battery & multi-meter "blk-lead to pin of "grey-wire) 12.72vdc There should "NOT" be voltage on this wire/lead in no-key position...right?

-So, started pulling back the leads attached to the harness and so far I can't find this mystery DC voltage. I have not yet pulled off the PCM plug, but at this point not sure what good this will do me. Continuity does not seem to be the problem, but this stray voltage is...I guess the grey wire could be shorting with the red wire somewhere, will continue to look and see what I can figure out. Just thought I update here and maybe someone may have run into this issue. Thanks again for the diagram.

Follow-up:
This evening I pulled the PCM cabling and tested for continuity:
-Both the red and grey wires tested fine to the pins holes to cabling on the diagram provided.
-Also, tested for shorts and could not find any between wires.
-I also tested for voltage on the corresponding male pins protruding from the "PCM"? And I have the 12vdc there on both the red corresponding & grey corresponding pins!!! I think its safe to my problem is not in the cabling or harness??? But, now what??? "PCM" issue???

cgallo
07-22-2015, 10:51 PM
According to your explanation you are measuring wrong.
1. always going to measure voltage place the black lead of the multimeter to GND or negative pole of the battery and the red cable to the element to measure the voltage.
2. I understand, you're doing it backwards, positive of multimeter in the battery positive and negative or black wire on the element to be measured, for this reason you are giving 12 v forever.


. measures as directed in 1 and tells me.

Please check that the alternator put the connector has not exchanged cables of position, red and gray.

I attached the file again with a photo at the end of it should be the alternator connector



Cesar Gallo

wiredawg
07-25-2015, 02:17 AM
Hey Cgallo...again, I thank you for your help. I thought I responded here a couple of days ago. I guess, the forum didn't take it...anywho, I got it fixed today, it ended up being a bad "New" off-the-shelf Alternator. I got another new another "New" one, installed it and everything is back to normal. :)
But, I did take all kinds of measurements. Seems like a waste if I didn't post them. At least this way someone else will have a baseline to go by and hopefully find this info useful. Okay here it goes, probably repeating some things but i think this is more definitive info:

So, if one replaces their alternator and it doesn't work and you think its your signal wires (the 2-wire plug to the alternator) here are some base line voltages that checks out to be good: (2003 Envoy XL 4.2l/6cyl)
-Negative battery post "DISCONNECTED":
--Red wire(generator-on) to meter "red-lead" & meter "blk-lead" to neg bat post=+12.52vdc
--Grey wire(field duty cycle) to meter "red-lead" & meter "blk-lead" to neg bat post=+12.62vdc

-Connected negative battery post (battery properly connected):
Good voltage readings from positive battery post to alternator casing and chassis ground +12.6vdc or so.

-No key in ignition with battery fully connected:
--Red wire(generator-on) to meter "red-lead" & meter "blk-lead" to neg bat post=no reading (didn't include this info since there was no reading the 1st time I posted)

--Red wire(generator-on) to meter "red-lead" & meter "blk-lead" to "+ battery post" = (-12.52vdc)...I know this is "NOT" standard measurement practice. But, it was the only reading I got at the time. I figured this info was better than nothing...guess, I was wrong...just confused folks. LOL

--Grey wire(field duty cycle) to meter "red-lead" & meter "blk-lead" to neg bat post=again, no reading

--Grey wire(field duty cycle) to meter "red-lead" & meter "blk-lead" to "+ battery post" = (-12.62vdc)...again, "NOT" standard measurement practice, just thought I'd include it.

-Key-in/"turned to 1st accessory position"(1 click):
--Red wire(generator-on) to meter "red-lead" & meter "blk-lead" to "neg battery post"=(+5.03vdc)
--Red wire(generator-on) to meter "red-lead" & meter "blk-lead" to "pos battery post"=(-7.31vdc)...and again, I know not standard measurement, just thought I'd include this)

--Grey wire(field duty cycle) to meter "red-lead" & meter "blk-lead" to "- battery post" =no reading

-Key-in/"turned to 2d accessory position"(2 clicks):
same readings as 1st accessory position.

The Problem I was having after installing 1st "New" Alternator:
-Started vehicle, loud squealing (sounds like serpentine belt squealing) but it was coming from the new alternator and no voltage change across battery post still reading about 12.5vdc-12.4vdc. Hence, not charging.
--I disconnect grey wire(spliced;for accessibility purposes) while still running; still squealing and no voltage change across battery.
--I disconnect red wire(spliced;for accessibility purposes) while still running: squealing stops and there is some engine load difference, a noticeable pause or load difference within the engine. (not sure how to describe it) but it was like turning an accessory on or off. Obviously, it was the alternator.

*Note*(Splice) I decided to cut my 2-wire alternator pig tail plug (this was also new, the old one broke a wire at plug while removing my original bad alternator) since, I had a good 12 inches of wire to utilize I decided to cut it and just splice them together and yes I did insulate with electrical tape to be sure not to accidentally short or ground them, while troubleshooting this issue. I only did this for a accessibility purposes. I've been dealing with this issue for several days. And could not wrap my head around my "New" alternator was the problem, even had it tested. I thought something was wrong with my signal wires. I do not recommend cutting your signal wires. In the end, I returned my "New" alternator for another "New" one, installed it and voila everything is working as it should be and all my voltages, checks out. :)