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

: [SOLVED] crazy problem with alternator


jimc
03-05-2011, 11:16 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, 11:47 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, 03:15 PM
thanks-I'll check and let you know.

jimc
03-05-2011, 05:03 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, 05:29 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, 06:11 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, 08:12 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, 09:24 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, 12:09 PM
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, 12:15 PM
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, 12:20 PM
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, 02:57 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, 01:13 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
03-05-2012, 12:17 AM
: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