2006 Trailblazer Alternator Woes

[dbrannon79]

Hey guys, I know I can ask on the trailvoy forums but I'm not a member there "yet" as I had posted in another thread we had the battery go bad on us. the battery was dated June of this year and somehow got smoked to where it would not take a charge. this was a couple weeks ago. I since swapped it with a spare battery I had and when I got it home, noticed that the voltage gauge was at the 3/4 mark indicating an overcharging condition.

Yesterday I finally got time to poke at it checking all the connections and probing with my multi meter. I swapped in a used alternator from the pick a part yard simply because I did not want to shell out $300 for a new one since this vehicle alternator is apparently controlled by the ECM. we also were able to get the smoked battery warrantied out so now it has another alternator and a new battery.

driving around tonight I noticed once again the gauge is back up to the 3/4 mark (14v is in the middle), got home and grabbed my meter. probed the battery and was seeing 14.7 with all the lights and AC running. turn it all off and it went up to 14.8v at idle. I even went as far as plugging in my Bluetooth obd scanner and looking at the ECM data which shows 14.5v.

to me this is kinda high and might have caused the other battery to get smoked.

looking online all the info I can find on this is for the 2007+ variants which have a sensor on the negative battery cable that is common to go bad and do this exact same thing. problem is this is a 2006 and does not have this sensor.

I am looking for possibly finding a GM service manual for this thing and hoping to find some help on what could be causing this.

this thing has left my wife stuck in town twice now where it would not crank. once with the original battery and once with the spare I installed. both times I went to the rescue the battery was dead. on the original battery, I could not jump it due to the battery being smoked, the second time I was able to jump it and get it home.

I seriously doubt the used alternator (which looks new with reman stickers still on it) would have the exact same issue and do exactly the same as the old one I pulled.

I plan to take the old alternator in to town and have it tested but then again I don't trust the local auto parts as much as I would a real alternator shop, but we don't have one of those here locally. If anyone knows where I can find a GM service manual online for it or has some knowledge about this, Please do tell!

 

[dbrannon79]

I did find a diagram for the charging system. doesn't tell me much other than confirming that the ECM/PCM controls the alternator through a pwm signal. looks like I might have to go through all of the power and grounds along with probing for any voltage drops between the battery and the PCM. from what I can tell and reading between the lines, if the PCM isn't seeing the right voltage it will just tell the alternator to output more!

This is where I really have to be careful since this thing has a CAN BUS system. it's not gonna be fun! Here is a pic I took tonight of the gauge and a snip of the diagram

 

[dbrannon79]

bookmarking this here to come back to. found some interesting information. this links to a 2004 but is most likely the same system as the 06.
read post #6

Help! Wife's 2004 trailblazer had a burning smell...

Hello all, The wife has a 2004 trailblazer with 180,000 miles on it. Yesterday, when she got home, she noticed a strong smell coming from the left side of the hood area. She described it as smelling like something was burning… Perhaps a belt or a hose and also a smell of some kind of fluid. It...

www.trailvoy.com

 

[dbrannon79]

going off the info in that post, I went out there and connected my charger to the new battery. the charger has a display that tells me the state of charge and it says the battery has an 80% charge. So I plugged it in and will leave it over night. in the morning I will see what the it does with a fully charged hot battery.

my suspicion is there is a connection issue to the PCM where it monitors the battery.

 

[WarWagon]

probed the battery and was seeing 14.7 with all the lights and AC running. turn it all off and it went up to 14.8v at idle.

Depending on temperature and battery temp the charging voltage will change. It must as batteries need different voltages to charge properly at a given temperature. Normal or not I wouldn't worry even at 15V with things cold. Warmed up it should go down noting GM likes the lower "float charge" voltages in the mid-upper 13's. I believe things like WOT, headlights on, etc. changed the voltages into the 14's. The Fuel Economy shut the alternator off mode I never liked as the first time it went off in a new 2005 model I thought I had an alternator failure.

Second alternator just proved it's likely not the problem. Or was the reman the usual "what is quality" now a problem unit?

You have a "Forget Tesla We have the Real Blazer" as electrical problems are known to burn Trailblazers to the ground. Blower motor wiring at the resistor pack, power window wiring off the top of my head.

A Big Three ground is something you should install. Big ground wire to the frame from engine, ground wire from body to engine, and ground wire from body to frame. Don't double it up on any existing ground wires unless you want more more alternator noise out of the OnStar mic. GM used a small joke of a wire out of the corrosion prone negative cable to ground the body to the engine.

Analog cell service era OnStar will OnSuck the battery dry. It's now looking for a signal that no longer exists. Make sure it's disabled. Fuse located off positive battery connection if I recall correctly .

The ignition switches "Old GM" used on these were not exactly reliable. I had a bunch of ghost codes on my 2007 Trailblazer SS. Paid dealer to change it. Popped OEM switch open at like 5000 miles on the ODO and tossed it's burnt contacts on the service manager's desk. They wrote me a check as it was now submitted as warranty. The burnt contacts would "Brown Out" the ECM with low voltage. Then things like A/C would randomly not work, random codes... New ignition switch cured it of course.

So monitor the ECM voltage and compare it to the battery voltage on your meter. Oh yeah the Ba#$%@# switch contact, accessory, is intermittent bad. When it's acting up the ECM voltage may be way low from your voltmeter.

 

[dbrannon79]

Depending on temperature and battery temp the charging voltage will change. It must as batteries need different voltages to charge properly at a given temperature. Normal or not I wouldn't worry even at 15V with things cold. Warmed up it should go down noting GM likes the lower "float charge" voltages in the mid-upper 13's. I believe things like WOT, headlights on, etc. changed the voltages into the 14's. The Fuel Economy shut the alternator off mode I never liked as the first time it went off in a new 2005 model I thought I had an alternator failure.

Second alternator just proved it's likely not the problem. Or was the reman the usual "what is quality" now a problem unit?

You have a "Forget Tesla We have the Real Blazer" as electrical problems are known to burn Trailblazers to the ground. Blower motor wiring at the resistor pack, power window wiring off the top of my head.

A Big Three ground is something you should install. Big ground wire to the frame from engine, ground wire from body to engine, and ground wire from body to frame. Don't double it up on any existing ground wires unless you want more more alternator noise out of the OnStar mic. GM used a small joke of a wire out of the corrosion prone negative cable to ground the body to the engine.

Analog cell service era OnStar will OnSuck the battery dry. It's now looking for a signal that no longer exists. Make sure it's disabled. Fuse located off positive battery connection if I recall correctly .

The ignition switches "Old GM" used on these were not exactly reliable. I had a bunch of ghost codes on my 2007 Trailblazer SS. Paid dealer to change it. Popped OEM switch open at like 5000 miles on the ODO and tossed it's burnt contacts on the service manager's desk. They wrote me a check as it was now submitted as warranty. The burnt contacts would "Brown Out" the ECM with low voltage. Then things like A/C would randomly not work, random codes... New ignition switch cured it of course.

So monitor the ECM voltage and compare it to the battery voltage on your meter. Oh yeah the Ba#$%@# switch contact, accessory, is intermittent bad. When it's acting up the ECM voltage may be way low from your voltmeter.

The ignition switch has crossed my mind as where the issue might be. my main thing is I don't what it to leave her stranded again for the same issue! I'm still trying to figure out what happened or what caused the spare battery I put in to go dead and leave her stranded. after I jumped it off, it was charging and all as if nothing was wrong that would cause it to go dead! Yeah it's an old battery I happened to have in the garage, but strange.

it's almost as if like you say, the alternator turned off or rather the ECM turned it off while she was driving and it went low and didn't start charging again till I jumped it.

WHY GM WHY did you let the ECM control things like this! the pre 2000's alternators worked just fine without the computer!!

 

[WarWagon]

Yeah it's an old battery I happened to have in the garage, but strange.

It takes some time to fully understand heat reduces battery life to maybe 2 years here. If some other failure doesn't kill a battery before then. You are in a slightly cooler hot area of the country right? An old battery is more suspect than anything. It's Reserve Capacity being very low with the alternator shuts off mode could have done it.

I would keep an eye on the replacement new battery voltage and call it fixed in a couple days.

Possible the first battery shorted a cell to boil dry.

You should still disable the OnStar battery parasite. It's more of a problem than ECM alternator control.

 

[dbrannon79]

I will look to see which fuse runs the onstar and pull it. or see what methods there are to completely disable it. it's old enough to use 3g cell towers that are now dead anyway.

 

[dbrannon79]

Welp I got out there this morning and seeing this... think there is something else going on here. my multi-meter shows 12.6 with the key off at the battery and still 14.7 at idle. but look at what the gauge is reading. first pic is key on engine off, second is at idle. mind you it's been running and now at full operating temp.


Key on engine off.


Engine at idle

 

[dbrannon79]

Looks like I will end up adding some aftermarket gauges!! plugged in my OBD reader and the ECM also shows a solid 14.5 regardless if I increase the RPM

 

[dbrannon79]

Disabled the OnStar, found the module under the passenger side rear seat. just removed all of the connectors and antennas.

for piece of mind I got my amp clamp out and measured the amp output on the wire to the alternator, battery, and main fuse block. the alternator only pushes 26 amps at idle, the battery is only getting about 4 amps and the rest is going into the main fuse block to the vehicle. So I am deeming the issue resolved with the exception of a faulty gauge in the cluster.

added to the list will be a voltage, oil pressure, and temp gauge to put somewhere in the drivers view. might try printing a custom pod for the pillar for it.