2007 LTZ - Voltage Gauge does NOT fluctuate any more.

Unlike most of the other related voltage posts I've read, my problem is that the voltage always seems to stay around the 14V to 15V.

In the past it used to go up and down as it should for this vehicle.

I have checked the voltage at the battery and it matches pretty much that on the instrument cluster. The circuits between the Current sensor and the BCM are all fine.

Does anyone know how to test the current sensor itself, or have any ideas what could cause this?   

Newer vehicles will lower the voltage as the battery gets charged... If yours is staying up it likely means your battery is not fully charging anymore.
This really normally only is caused by 1 of 3 reasons...
Loose or corroded wire connector(s) - the main wires to check are the alternator to battery wire and the ground to the block.
Weak alternator - if one diode goes out it will still half work but you MAY hear lots of noise on your radio or see lights flicker etc.
weak battery - Your just not able to charge it fully anymore. If this is the case you will likely find out in the winter if it is bad enough...

Most likely the wiring or the battery unless you are seeing the other issues such as flickering lights or radio static.

Thanks, I'll check the wiring today.

I did change the battery to a bigger one and calcium.

Could it be that the Avy charging system is not enough for a Calcium battery perhaps?

OzAvy said:

Thanks, I'll check the wiring today.

I did change the battery to a bigger one and calcium.

Could it be that the Avy charging system is not enough for a Calcium battery perhaps?

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Calcium? Never heard of those...

Bigger generally doesn't matter if your only using as much power as you were before on a daily driven vehicle.

Biggest issue with batteries is making sure they are compatible with your vehicle charging system.

Would be interested in hearing more about this battery you have... It is likely to be related to your battery if you just changed it. Very important to make sure you check out the wiring at this point and make sure everything is clean and solidly connected.

Rodney

Just looked up the Calcium batteries...

Normal Lead Acid batteries need 14.4 volts to charge. a Calcium battery requires 14.8 volts. It looks as though your system isn't charging the battery at a high enough rate so you are not charging your battery but your alternator is trying to..

So if it is not dropping off I would suggest that the battery you have is not compatible with your trucks charging system. You either need to get a different alternator that can put out the 14.8+ volts as needed or go with a different battery. I wouldn't go away from the standard Lead Acid batteries. Other batteries really just burn your money up unless you have a large audio system or go off roading a lot and use a winch. Even then I wouldn't bother with an AGM unless they are on sale. There are high purity type batteries and others that can be used for different things. It looks like Calcium batteries really are more of a specialty battery and really not a good idea for older vehicles.

Older sound systems benefited from fast discharging batteries such as the Optima when running high powered subwoofer systems but using such a battery on a vehicle with little to no extra stuff is just throwing money away.

If your alternator is driven harder than designed you will start blowing Diodes or at a minimum prematurely wear your alternator...

Getting a bigger alternator won't help because it is the voltage your trying to raise, not the amperage... And if you run an alternator that CAN do 14.8 volts you MAY start taxing other systems in your truck if they are not designed to run at a higher voltage all the time.

Thanks Rodney, I'm still looking.

I think that my battery is actually still effectively a lead acid battery with calcium additives. The manufacturer calls it a lead-calcium battery. So maybe the battery is not the problem. To help confirm this I ran my old OEM Delco battery for a couple of 25 mile trips. Its seems those batteries go forever, once the old thing charges up it can still start the engine quite well if not left standing too long. Anyway the voltmeter was still in the same position so it seems like I have not found the answer.

One thing I did do in the past, ironically to try and prolong the life of my original battery, was to turn over on the cable the current sensor. This causes constant charging without a DIC message. The current sensor was left in this position for a couple of years I think, but as of just before the start of my post here, I had turned it back over to the right direction. I doubt it, but do you think I may have damaged the BCM charging logic by having the current sensor the wrong way around? The three wires at the current sensor test alright except for one. According to the service books, one is set to ground (OK), one at 5V (OK), and the other, which is also meant to be 5V, I test at 4.5V.

Can the BCM easily be re-flashed just in case?

Philip

redheadedrod said:

So if it is not dropping off I would suggest that the battery you have is not compatible with your trucks charging system. You either need to get a different alternator that can put out the 14.8+ volts as needed or go with a different battery. I wouldn't go away from the standard Lead Acid batteries. Other batteries really just burn your money up unless you have a large audio system or go off roading a lot and use a winch. Even then I wouldn't bother with an AGM unless they are on sale. There are high purity type batteries and others that can be used for different things. It looks like Calcium batteries really are more of a specialty battery and really not a good idea for older vehicles.

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The output voltage is not controlled by the alternator, but by the BCM.
A flash may or may not help, but you don't need a new alternator to use that battery, no matter which alt you choose it's output V will be externally regulated.
If you want to keep that battery, you can always get an external Voltage Control Module that overrides the BCM. I use one from SMD for turning up the output of both my alts to 15.4 for competition.
Some have completely variable user controlled output from 12.5 to 18.5V. Some have set points that you can choose from. You can set it to the 14.8V number that is needed (if that is the case) and forget it. A few reputable companies make them.
Mechman makes one that has a control knob you can put in the cab. I believe they call it an AVBM (Adjustable Voltage Boost Module)
Missing Link Audio (MLA) makes one with preset points that you can select and leave under the hood (they call there's a VCM - Voltage Control Module)
XS Power makes them with digital readouts and adjustable in the cab - also called a VCM
I don't believe the SMD one that I have is still in production.
Either way, there are easy ways to control your alt output if that is your ultimate goal here.
If your goal is achieve the factory condition of the output voltage dropping at system capacity to prolong longevity of the charging system that's as simple as buying an OEM or OEM replacement battery.
Do you have a bunch of aftermarket accessories that you need this "Upgraded" battery you purchased for?
I'm sure you have already checked this, but using the "tow" mode disables this feature. You aren't driving around with the tow mode engaged are you?

Calicak89 said:

If your goal is achieve the factory condition of the output voltage dropping at system capacity to prolong longevity of the charging system that's as simple as buying an OEM or OEM replacement battery.
Do you have a bunch of aftermarket accessories that you need this "Upgraded" battery you purchased for?
I'm sure you have already checked this, but using the "tow" mode disables this feature. You aren't driving around with the tow mode engaged are you?

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Yes, thanks, tow mode is certainly off and I've even checked the wiring diagrams to see whether different (perhaps stuck) solenoids turn on the stiff suspension and shift points separately.

I moved to the bigger capacity battery to try and overcome the affects of all the parasitic loads, and also before this battery turned the current sensor upside down for a while. I do not have any current hungry accessories.

I've now tried running my old battery for a while but maybe for not long enough or it can't be fully charged now eh?

Do you know how I can test the current sensor at all?

OzAvy said:

I moved to the bigger capacity battery to try and overcome the affects of all the parasitic loads, and also before this battery turned the current sensor upside down for a while. I do not have any current hungry accessories.

I've now tried running my old battery for a while but maybe for not long enough or it can't be fully charged now eh?

Do you know how I can test the current sensor at all?

Click to expand...

The PCM and Radio have a no-run, or parasitic draw on the battery, but the two of these combined shouldn't be be more than 25 milliAmps, or .025 A these should be the only items pulling draw once the ignition is in the off position and the vehicle has "gone to sleep"
At rest, the draw on the battery should be <30mA. 
Maybe you have something more in depth here than just these two draws affecting your system.
This doesn't really answer your question, but maybe your issue that started all of this (weak/dead battery) was caused by another electrical gremlin and not just being a "worn out" battery.
I do not know if it is possible to check the functionality of the current sensor as I've never really dealt with it as I bypass its functionality. My bet on those in the know would be MS03 2500, Enoniam, RedheadedRod or RontheHandymanGA. one of them might be able to tell you.

Did the parasitic draw start before or after you messed with the sensor?

Your best bet to always track down the draw instead of trying to figure out a work around.

With such a small draw it should be somewhat simple to track down. MOST Volt Ohm Meters have a amp test feature for under 10 amps. And you should be well under that.

So what you do is rig up a connection from the battery to your power source and measure your draw. Then start pulling fuses in the under hood box until you find the one you pull and the draw goes away.

Note that some modules will likely pull power all the time. (Which is why when you leave your vehicle parked for a month or more you pull the negative battery cable.)

Radio may pull some power when off since it is controlled by the data bus.
BCM may pull power because it is looking for a start command or other traffic from the VCIM or Door Modules.
Door modules - looking for unlock commands. Passenger side door module also contains key fob computer in 2006 and earlier. May also for older.
VCIM (Cellular connection) This is active for those with Onstar to get commands from "the mother ship".

You may find other modules pulling power too but they SHOULD be very low power and may not even show on your VOM.
Your looking for something pulling more power than you would expect.

The Audio system can be prone to draw if one of the components are damaged such as the amplifier, radio or RSA/RSE.

If you modified your alternator wiring your alternator could be "on" all the time. I seem to recall someone tracing their parasitic draw to the alternator...

Also have heard of the starter solenoid staying partially engaged too...

Note if your truck is like my '03 there are two wires coming from the battery. A small one going to the under hood fuse box and the large one that goes to the starter. Since it goes directly to the starter you may find you want to test this wire all on its own. (Mine also has the alternator tied to it so I would have to disconnect the alternator to check. Or you could check the two together by testing this wire on its own. Should draw 0 when the key is off.)

I would test the rest of the truck by disconnecting the 8 gauge wire from the under hood fuse panel. This panel feeds everything NOT the starter...Although it feeds the solenoid.

Sorry gentlemen for the delay in replying.....

I've now tested idle (vehicle sleeping) current draw and its as it should be, tiny. I had perceived that it was more because of the much larger initial current draw when the battery cable is first connected, judging by the strong spark. I had never before actually connected up an ammeter and waited for things to settle - my wrong.

I have also tried running the truck with a much smaller battery out of our 2002 Jeep Cherokee Limited V6. Again the voltmeter did not go down.

Now I think I probably need to have a closer look at the alternator.

I've also placed a call to the electrician at the shop where I bought the truck to see if he has any ideas. Buy the way, I'm in Australia and the Avalanche was converted to RHD.

I haven't heard anyone ask what the voltage is with the key on engine off.  If it's still 14, then the gauge is inop.

If gauge is inop, check what voltage PCM sees using a scanner with KOEO.  If it doesn't match the gauge, then the stepper motor for the gauge is probably bad.  Other gauges working checks the serial data line which is common to the gauges in the instrument cluster.  There are services that fix stepper motors in these instrument clusters or you can get kits on-line.

If PCM is seeing above 14 with KOEO, then check actual battery voltage with a digital multimeter as something is very screwey..

Hope this helps

OzAvy.

Way back in the early days of this forum, there was a very active member from Australia named Skidd who had a RHD Av.

http://www.chevyavalanchefanclub.com/cafcna/index.php?action=profile;u=1394

Hey Sirs....I think the problem has gone away by itself! Well pretty much

The only thing I did was to pull off the generator, remove the plastic cover over the rectifier and check the small torx bolts that hold down the rectifier assembly. One of them may have been loose.

If this was the fix, it still took a few weeks of driving before the voltage gauge came good.

Right now I'm not too concerned about what fixed it, perhaps enough time for the logic to recover after I flipped the voltage sensor and later put it back!

Good old Chevy