2007 SSV not charging, but good alternator and battery

[Toonces]

New to me 2007 SSV has charging issues. First noticed a "Service Charging System" message in the DIC and the voltmeter staying way low, but eventually popping up to around 15V once the engine ran a while and I'd revved it a bit. At some point the warning message would disappear. I didn't realize it has the adaptive charging nonsense so I figured it had a failing regulator and took it to a well regarded shop with instructions to fix it *right*. They wound up replacing the slip rings, brushes and bearing, and claimed it tested fine.

So I confidently reinstalled it, only to find the battery light is now on full time, as is the "Service Charging System" message. Grrr.

A bit of DuckDuckGo-ing informed me about adaptive charging and suggested the most likely culprit was a blown fuse in the alternator output circuit. Alas, the fuse is fine and the output post on the alt measures battery voltage with the engine off, so there seems to be a good path to the battery. The battery is 6 months old and tests fine with my fancy tester; it also takes a charge just fine from an external charger, so the battery, alternator, and the connection between the two all seem to be fine.

Can anyone suggest any "they all do that" areas I haven't heard of yet? I'm a Euro car guy so I don't have a Tech 2 and without a proper scan tool I'm out of ideas. Hoping you guys can supply some. Please... my experience so far with this truck has been pretty disheartening. :-(

 

[j91z28d1]

I have no idea what shop you found that rebuilds alternators and I've found telling anyone to do something "right" these days leads to them doing it anything but right.

what's your voltage at the alt battery terminal when running? with black lead on the alt case and on the battery neg? if you unplug the small 2 wire plug the alt if working correctly should default to 13.7 volts.


I'd start there. honestly sounds like you have a bad alternator and having things rebuilt these days isnt the most reliable. I've completely stopped using alternator and starter repair shops at my job after they cost me more time and money than just buying new stuff.

 

[Toonces]

Thanks very much for the reply, j91z28d1

What I meant by "fix it right" is that I asked them to use American bearings and quality parts throughout, as they would in their wives' cars, and that I was willing to wait for quality parts if they weren't in stock. Whether they actually did that is unknown.

It's not your typical hole in the wall alternator shop and we had decent luck with them repairing hard to get items back when I had my shop, but they may have changed owners since then, so who knows. I figured the odds were as good with them as they are with Delco these days.

Tell the truth, I did buy a new (not rebuilt) ACDelco alt, but it was packaged so poorly the black connector broke in shipping. Just one of the many frustrations I've had trying to get this truck sorted...

As to your other questions, voltage at the output terminal with the engine running is the same as battery voltage: 11.92. With the engine off it's ~12.46 both places.

Voltage drop on the positive leg of the circuit is .01. Voltage drop on the ground leg is .03.

Unplugging the black connector made no difference, but the service manual & online sources indicate that one pin of the connector is the PWN control wire from the powertrain control unit. If that's true I can see why there would be no output with it disconnected unless there's some sort of "fail safe" switch inside the alt, and that sounds awfully generous for GM. ;-)

However, you've got me thinking that it makes sense to try to confirm that the alt is actually good, so I'll try to find a parts store that can test it and report back.

If all else fails I haven't returned the new alt with the broken connector. I was close to installing it but was afraid that it showing any signs of use would prevent me from getting a refund.

Again, I appreciate the reply and hope the answers to your questions will inspire further suggestions.

 

[j91z28d1]

yeah. there's a very long 100 pages thread about these 2 wire pwm alternators over on lstech. I have used one of the 220amp ones from these trucks on my c6 that doesn't down pwm control. first by just letting it default to 13.7 volts. then layer installed a add on pwm controller and upping it to 14.5.

2 pin 2006 + alternator. Don't throw it away!! - LS1TECH - Camaro and Firebird Forum Discussion

Conversions & Swaps - 2 pin 2006 + alternator. Don't throw it away!! - I just swapped the regulator in my alternator from 4 pin to 2 pin, so now it's like a 2006 or newer alternator. Why??? Because GM thinks it's better than the older 4 pin one and they must know something. Oh but everyone says...

ls1tech.com

if you have nothing while running, it's a dud. you can try swapping the other one in. I personally found a low mileage 220amp take off on ebay. they go for around 100$. funny mine also came with a broken 2 wire connector. so I contacted them and they sent me a 2nd alt, this one was a different part number, a 180amp but it would have worked. I just didn't want it. so I asked if they wanted me to sent it back and I'll just keep the first one and zip tie it on or something, as this was going be be modified and clocked to fit the different bolt spacing of the c6 brackets anyways. they said nah, keep both and refunded the money. so in the long run, it worked out well. I have a spare.

but the 220amp is a good upgrade and direct bolt on for your truck. since it sounds like you need a new one anyways. the part number and install threads are around there somewhere. only reason I haven't done it to to my yukon is I happen to have a hybrid one that doesn't have a belt driven alt. but I definitely would as I've had great results. thing will put out over a 100amps at idle with under drive crank pulley workout breaking a sweat. I would personally do the 100$ used oem 220amp over the $500 plus aftermarket alternatives for these trucks.

 

[Toonces]

Thanks again! Great info. I'll go look at that thread and determine how I want to proceed based on what I learn. I guess this is good news because there is a warranty on the work performed by the rebuilder so you can bet I'll be having a discussion with them. I just want to be 100% confident so I don't accuse them of something they didn't do and then demand they repair it.

My truck is an SSV, which is the 4x4 version of the PPV (Police Pursuit Vehicle) so it has a 160 amp alternator and additional power distribution circuits from the factory. 160 is fine for my purposes since this is just a daily driver-- I prefer my truck mod budget to go to my '95 Z71 2 door Tahoe, which is in need of an alternator upgrade (I was thinking Mechman), but I need to upgrade the charging circuit and grounds before adding that much charging current.

Anyway, looks like I need to read up on this stuff and also see if there's a parts store that can bench test that alternator. but this is definite progress, and I thank you for it. Since I'm not familiar with GM's adaptive charging technology I automatically started chasing the unknown, instead of considering that the refreshed alternator might still be causing problems. Thanks for everything!

 

[j91z28d1]

only thing to remember, is it's possible to request down to 11v charge via pwm. so unplug the 2 wire and test it. Just incase there is something wrong with the pwm signal from the ecm.


I had a 96 2 door z71.. miss that thing, sold it about 2 years ago to a guy thru here with 325k on it. never let me down. such a good old truck.

don't waste your time on the mechman stuff when oem is very good and easily available. check into the diesel alt for the obs tahoe. that's what I did, I had full electric fans and all, the stock one couldn't keep up even over driven. the diesel is a direct bolt on, larger case. it powered everything without issue and was 120$ at the local parts store with lifetime warranty. there was a full how to back in the day for it too. it's been a good 15 years since I did the mod thou.

I guess I shouldn't said direct bolt on, it's been a long time, but I think a rear bracket they isn't really needed but can be modified to fit. and upgrade to a thicker power cable, mine was getting warm to the touch with everything on. it can output a lot of amps even at idle.

 

[j91z28d1]

High output alternator

I've seen some posts about this, never seen a complete write up with part numbers, so here goes. Been looking to do this upgrade for a while, as usual I was forced into it, had to make a couple of decisions in the interest of time. As a lot of you know and a few threads on this site will tell...

www.gmt400.com

 

[Toonces]

I did unplug the two wire connector per the instructions in your first post. Zero change. Either their an issue with the PWN signal from the powertrain control module or the alternator is bad.

Going to check with a parts store in a bit in hopes they have a bench tester. I'd rather go back to the rebuilder secure in the knowledge that the alt is bad than to go in saying I *think* it's bad, because we both know they hear that a lot and prolly won't take it all that seriously.

Those two doors are great, aren't they? They weirdly split the difference between a half ton truck and a Jeep, but in a good way for my purposes. Mine has the tailgate, so cargo capacity is better than on my '07. It's in decent shape & would make a good restomod candidate, so it's going to get more love than the '07.

You nailed the reason I'm looking for more charging in the '95-- it has the slightly smaller factory alternator, but I swapped the mechanical fan for a pair of electrics and want to make sure the total consumption is met at idle so the fans are always spinning at full speed. Hence the interest in Mechman, since their 6 phase unit seems perfect for my application. But I hadn't even thought of a diesel alternator, which makes a lot of sense because it's for a low RPM application like mine. Thanks for the advice and link! Definitely worth checking out.

 

[Fless]

It seems like a decent scan tool would show the commanded generator duty cycle, and maybe the value of the "turn on" signal. Here's the electrical diagram (scroll down to the second diagram - charging), but use the links at the top to select the correct vehicle if this isn't yours.

Electrical Diagrams — 2007 Chevrolet Tahoe 2WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2007 Chevrolet Tahoe 2WD V8-5.3L.

charm.li

This one has voltage values for some of the control wires:

Charging System Test — 2007 Chevrolet Tahoe 2WD V8-4.8L Service Manual | Operation CHARM

Detailed repair manual for the 2007 Chevrolet Tahoe 2WD V8-4.8L.

charm.li

 

[j91z28d1]

I did unplug the two wire connector per the instructions in your first post. Zero change. Either their an issue with the PWN signal from the powertrain control module or the alternator is bad.

Going to check with a parts store in a bit in hopes they have a bench tester. I'd rather go back to the rebuilder secure in the knowledge that the alt is bad than to go in saying I *think* it's bad, because we both know they hear that a lot and prolly won't take it all that seriously.

Those two doors are great, aren't they? They weirdly split the difference between a half ton truck and a Jeep, but in a good way for my purposes. Mine has the tailgate, so cargo capacity is better than on my '07. It's in decent shape & would make a good restomod candidate, so it's going to get more love than the '07.

You nailed the reason I'm looking for more charging in the '95-- it has the slightly smaller factory alternator, but I swapped the mechanical fan for a pair of electrics and want to make sure the total consumption is met at idle so the fans are always spinning at full speed. Hence the interest in Mechman, since their 6 phase unit seems perfect for my application. But I hadn't even thought of a diesel alternator, which makes a lot of sense because it's for a low RPM application like mine. Thanks for the advice and link! Definitely worth checking out.

yeah the newer oem 220am is a 6 pole. I'm pretty sure one of those would fit your obs as well, and then as seen in that lstech thread, a 20$ pwm box can be used to set it to any voltage you want. I use the little blue one and it's solid. can adjust it to anything I want. like I run a Optima agm battery in it. so I emailed them and got a good voltage it likes to be run at and set it to that. next I believe the sodium based batterys will be easy to get. I want to try one, so I will adjust the voltage to what that likes.