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Discussion Starter #1
First I replaced the battery with a new one, while running for 2minutes the car displayed "Service battery charging system" then "Battery Saver Active"

So I went ahead and got my alternator rebuilt(I live in BC, Canada) considering none are new anymore anyhow.
Put the alt back in, started up at 13.8 volts but started to drop .01 every 10seconds until it couldnt power the car anymore and died, rev'd to 2k and 3k still no charge.

Now when I get the car jumped it wont charge passed 12.4 volts, and it drops from 12.4volts to 11v as soon as I unhook jumpers.
Then takes 2mintues to die at 8vs and even went down to 7volts. Its dying faster than ever.

So bother alt and battery are new, Batter does hold its charge overnight while plugged in. Only start to lose power when car is on.

I pulled every fuse to check them, by eye nothing looked wrong.

Im stumped and frusturated, for 2 days before my alt gave out and these problem started to occure, i had a transmission flush and oil change. After that appointment when i was looking at my alt there was oil on the back of the alt and inside, and im pretty sure Cadillac spilled oil on it, either way it got fixed.

So with new alt and battery still dying,

Could it be that I need to replace the starter, maybe its bad and drawing more power? from the 3 years of me owning it I haven't replaced the starter. Either way when it starts the battery starts to drain.

Do I need to get a new alt sensor?
Do I need to get new wiring if so from where to where?
Also how would you check for faulty grounds?
Or how do I check if there is an accessory problem, as if something were keep turned on, either way what could be draining the power so much to drop the charge to quickly? Perhaps the ground?


Thank you for any help!

Here are 2 pictures of how it looked before I got the alt rebuilt.
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

It might help your diagnosis if you knew how the system works.

Generator

The generator is a serviceable component. If there is a diagnosed failure of the generator it must be replaced as an assembly. The engine drive belt drives the generator. When the rotor is spun it induces an alternating current (AC) into the stator windings. The AC voltage is then sent through a series of diodes for rectification. The rectified voltage has been converted into a direct current (DC) for use by the vehicles electrical system to maintain electrical loads and the battery charge. The voltage regulator integral to the generator controls the output of the generator. It is not serviceable. The voltage regulator controls the amount of current provided to the rotor. If the generator has field control circuit failure, the generator defaults to an output voltage of 13.8 volts.


Body Control Module (BCM)

The body control module (BCM) is a GMLAN device. It communicates with the engine control module (ECM) and the instrument panel cluster (IPC) for electrical power management (EPM) operation. The BCM determines the output of the generator and sends the information to the ECM for control of the generator turn on signal circuit. It monitors the generator field duty cycle signal circuit information sent from the ECM for control of the generator. It monitors a battery current sensor, the battery positive voltage circuit, and estimated battery temperature to determine battery state of charge (SOC). The BCM performs idle boost.


Battery Current Sensor

The battery current sensor is a serviceable component that is connected to the negative battery cable at the battery. The battery current sensor is a 3-wire hall effect current sensor. The battery current sensor monitors the battery current. It directly inputs to the BCM. It creates a 5-volt pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0–100 percent. Normal duty cycle is between 5–95 percent. Between 0–5 percent and 95–100 percent are for diagnostic purposes.


Engine Control Module (ECM)

When the engine is running, the generator turn-on signal is sent to the generator from the ECM, turning on the regulator. The generator's voltage regulator controls current to the rotor, thereby controlling the output voltage. The rotor current is proportional to the electrical pulse width supplied by the regulator. When the engine is started, the regulator senses generator rotation by detecting AC voltage at the stator through an internal wire. Once the engine is running, the regulator varies the field current by controlling the pulse width. This regulates the generator output voltage for proper battery charging and electrical system operation. The generator field duty terminal is connected internally to the voltage regulator and externally to the ECM. When the voltage regulator detects a charging system problem, it grounds this circuit to signal the ECM that a problem exists. The ECM monitors the generator field duty cycle signal circuit, and receives control decisions based on information from the BCM.


Instrument Panel Cluster (IPC)

The IPC provides the customer notification in case a concern with the charging system.There are 2 means of notification, a charge indicator and a driver information center (DIC) message of SERVICE BATTERY CHARGING SYSTEM if equipped.
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There is a first and second design on the battery current sensor, depending on whether the sensor sees five volts from the BCM or ten volts.

The part number for the five volt sensor is 13505369, the ten volt sensor is 10306471. Both sell for about $22 US.
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

I have read on this forum where folks have bought new/rebuilt alternators that are faulty. Check out your alternator to see if it is good or not.
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

I have read on this forum where folks have bought new/rebuilt alternators that are faulty. Check out your alternator to see if it is good or not.
It's kinda hard with these newer alternators without the regulator. You can check for output at the alternator, but the absence of it isn't necessarily the alternator's fault.
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

The key word is "rebuilt" ....First make sure the battery is not defective. You need a good battery to excite the alternator into charging the battery. Once you prove out the battery then prove out the alternator. You should get at least 14 volts while charging, once the battery is fully charged the voltage will drop down to a little over 12 volts. I have had issues with rebuilt in the past it is possible the alternator is not working.

Best of luck
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

My guess is a faulty rebuild. As you probably already know oil is death to an alternator.
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

start your car up, remove one of your battery posts, see if your car still runs, if it's running the alternator is still working, also did you put a high amp battery in your car? It takes a lot of amps To keep all the electronics running in the CTS.
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

start your car up, remove one of your battery posts, see if your car still runs, if it's running the alternator is still working, also did you put a high amp battery in your car? It takes a lot of amps To keep all the electronics running in the CTS.
I do not recommend doing this with newer computerized vehicles. The battery acts as a regulator and disconnecting it can cause a voltage spike and possibly fry your
electrical system.
 

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Discussion Starter #9
Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

Heres my update, I guess I have unfortunate luck atm..

First battery was garbage, got a new one, that was garbage.
Alt gave out, got it rebuilt and still not working,

Went to get car check, alt isnt powering or charging car, go figures. Got to fix alt again lmao. Tomorrow gonna check it and replace alt once more and that should be all.
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

Wow! what a calamity of horrors. Best of luck with the next attempt, thank you for updating us.
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

Charging

re: Post #2 by douger...great informative post!!

.............You need a good battery to excite the alternator into charging the battery. Once you prove out the battery then prove out the alternator. You should get at least 14 volts while charging, once the battery is fully charged the voltage will drop down to a little over 12 volts.....
I believe that "exciting or flashing the field" is something done to old automotive generators and not alternators? A good alternator will charge a completely dead (but otherwise good) battery.
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

I agree that an alternator can charge a dead battery ( not recommended) I also agree that an engine will run with alternator voltage and a dead battery (also not recommended. I disagree with your thoughts on an alternator not needing excitation voltage. This thread below is great reading for anyone interested in learning how an alternator and battery work.

http://www.ratwell.com/technical/ChargingSystem.html

Happy Motoring!
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

I believe that "exciting or flashing the field" is something done to old automotive geezers
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

I already got one G.D. Infraction from the mods. This forum can be a little constricting sometimes.

And I have the other picture in my private stash.
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

Hahaha excellent!! now that's flashing!
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

I agree that an alternator can charge a dead battery ( not recommended) I also agree that an engine will run with alternator voltage and a dead battery (also not recommended. I disagree with your thoughts on an alternator not needing excitation voltage. This thread below is great reading for anyone interested in learning how an alternator and battery work.

http://www.ratwell.com/technical/ChargingSystem.html

Happy Motoring!
Great article. Thanks for posting.
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

Okay Basspopo, I see you are a new member, probably having joined for the miracle cure for your problem. As you can already tell, there are a number of opinions on this issue and none that appear accurate. Hopefully, very few get hijacked with the images that should be placed somewhere else. Pay attention to the rare poster who actually knows something or be prepared to buy unneeded parts and spend time replacing good ones.
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I have the exact same issue that you do (2008 CTS). Service Charging System notification. Dealer diagnoses bad Alt. and weak battery and wants >$1,000.00 to fix. I take to DIY. New Battery. I try rebuilt alt's from AZ and O'Reilly. Neither work at all. I buy new GMPartsdirect.com alt and think the problem is cured. <2 months later this alt goes bad. Now on 2nd GM alt. waiting for it to go bad.

What I am seeing is voltage fluctuation from around 12v at startup to no more than 13.8 volts at highway speeds. The fluctuation is constant and lessens in severity as the voltage increases. I was hoping when reading your post that someone would at least confirm that this is unusual. Of course, the dealer says bad alternators but I suspect more.

My guess is the ECM.
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

Life must suck when you have all work and no fun.

bkhitchens, you are guessing your ECM is the culprit. Why post an opinion just like any other flying guess on the internet?

Voltage does fluctuate on these cars, anywhere from around 12v at startup like you observed up to 14.8 while driving like I have observed over the last few years. Seems normal to me with my car at least. Also note that new batteries do go bad, and they can do it immediately after installation or a couple of weeks later, just like any battery. I have seen this. Same with alternators. You did a smart thing getting an OEM alt, but I am sorry that has failed as well. A good electrical shop is probably in your future. I would not take it to the dealer either. All they do is hit or miss things while you just throw money at the problem.
 

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Re: 2008 Cadillac CTS New Alt and new batter, losing power and not chargeing

You mentioned a 5 and 10 volt sensor. Does the CTS have both of these, or just one?
 
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