15.2 -15.4 Volts At My Battery

GMC Jug · December 10, 2009

Hello all.

I tried the search, but couldn't find an answer.

I have a 2006 GMC 1500 with the 5.3

I have 15+ volts at my Battery, (actually from my alternator).. It should be around 14.1-14.2 max right?

My question is this, Does my truck have an external Voltage Regulator? If not, the voltage regulator must be inside the alternator? So to replace it would mean a new alternator?

Any other things I should check?

All my Grounds are tight and secure, all the power wires I have found are free from nicks, and have no shorts that I can find.

Thanks.

Jug

dlstewart01 · December 10, 2009

What did you check it with? You know the gage in the cluster is not that accurate.

GMC Jug · December 10, 2009

I was checking it with a multimeter.

My Inverter is what tipped me off, it kept shutting down.. I bought a new one, and it did the same thing.

I found out it was going into over voltage shut down. That's when I started checking things.

The inverters are only good to 14.4 or so.

rodram · December 10, 2009

.. how much have you used the invertor?... and what kind of load are you regularly putting on it?

.. these invertors can play hell with alternators and voltage regulators.

dlstewart01 · December 10, 2009

here's a bulletin

Document ID# 2042756

Subject: Information on Voltmeter Gauge Fluctuation Due to Regulated Voltage Control System and Concerns About Camper/Trailer Battery Charging #07-06-03-009 - (12/05/2007)

Models: 2005-2008 Cadillac Escalade Models

2005-2008 Chevrolet Avalanche, Silverado, Silverado Classic, Suburban, Tahoe

2005-2008 GMC Sierra, Sierra Classic, Yukon Models

Voltmeter Fluctuation Condition

Some customers may comment that the voltmeter is fluctuating between 12 and 14 volts on their full size pickup or utility vehicle. Starting with the 2005 model year, light duty full size pickups and utilities are equipped with a new Regulated Voltage Control (RVC) system. This system reduces the targeted output of the generator to 12.6-13.1 volts when in "Fuel Economy Mode" to improve fuel economy. The generator may exit "Fuel Economy Mode" if additional voltage is required. This will cause the voltmeter to fluctuate between 12 and 14 volts as opposed to non-regulated systems that usually maintain a more consistent reading of 14 volts. This fluctuation with the RVC system is normal system operation and NO repairs should be attempted.

Camper/Trailer Battery Charging Concerns

Some customers may comment that when towing or hauling a camper/trailer, the auxiliary battery for the camper/trailer will not stay charged. In most cases, this concern is blamed on the new RVC system. While the RVC system does reduce the generator's targeted output voltage to 12.6-13.1 volts when in "Fuel Economy Mode", this feature is bypassed if the tow/haul feature is enabled. With the tow/haul feature enabled, the RVC system will stay in "Charge Mode" and the targeted generator output voltage will be 13.9-15.5 volts, depending on the battery state of charge and the estimated battery temperature. To keep the generator in the "Charge Mode", use either of the following two methods.

• The first method is to use the tow/haul mode when towing or hauling a camper or trailer.

• The second method is to turn on the headlights, which will increase the generator's targeted output voltage to 13.9-14.5 volts.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION

rodram · December 10, 2009

.... holy shit Batman!

... another big check mark on the PRO side for keeping my GMT400

... these newer ones get so damn complicated

GMC Jug · December 10, 2009

.. how much have you used the invertor?... and what kind of load are you regularly putting on it?

.. these invertors can play hell with alternators and voltage regulators.

The inverter was used for a playstation 2 for dvd player use. The screen used is 12volts, so it's not on the inverter.

The amp draw from the playstation is very minor.

I have used 3 different inverters in this truck (at different times) , a small one that plugs in the the cigarette lighter, an 800watt fed directly from the battery (fused), and a 400watt fed the same way. I've been using inverters for a long time, and I never use one that can't handle twice what I'm using it for. I've never had an issue like this in any vehicle, and probably have had inverters in 4-5 vehicles back. If used properly, I think it's unlikely that's the root of the issue. It was just the tip off to the problem.

GMC Jug · December 10, 2009

I just went and checked my "tow/haul mode".. this was off. It also resets with the ignition.

If this is the issue, it could be a relay stuck closed? The button seemed to work fine, and the light on the dash went on and off like it should.

It would make sense that the light is fed from a signal from the closed relay? Or is this an input from the computer and not a relay?

Thanks for everyone helping me.

dlstewart01 · December 10, 2009

sorry.... not wanted.....

GMC Jug · December 10, 2009

Thanks for showing me those bulletins, but it's possible I didn't convey my issue correctly.

None of those have anything to do with my problem.

Those discuss a fluctuating low voltage condition. I have a constant over voltage situation, not an under voltage while driving and trying to gain fuel mileage. ;)

The only time it references a higher voltage is when it talks about it being in towing mode, which is not relevant here as I'm not in towing mode, and have a very light load on the battery...at Idle, lights off, fan off...ect.

rodram · December 11, 2009

... you got something in the electronics in that 2006 related to the Regulated Voltage Control that is keeping your battery/alternator at that 15-15.5 Volt range in "Charge Mode" .... I am sure that there is more to that RVC system than what was discussed in that short TSB that Don provided..... just use that information to point you in the right direction, rather than disregarding it all together....

... maybe, and I am guessing here.... your battery itself is causing the RVC to stay in Charge Mode ... it might be a long shot, but drop a different battery in there for a test and see if the alternator responds differently

... or maybe you have something causing enough load on the battery that the RVC system kicks into Charge Mode

... invertors can be useful to power your little toys, but if the truck rejects them then you are SOL

minibike132 · December 11, 2009

How cold is it outside where you are?

GMC Jug · December 11, 2009

I didn't mean to dismiss the bulletins, and I wasn't trying to be rude. I'm very sorry it came across that way.

I sincerely appreciate the help and opinions that are being offered.

It's in the low 20's/high teens at night and mid/high 30's during the day. I wondered if the temp could be an issue also, but sometimes it's fine, it's very difficult to trouble shoot.

So this after noon I went out and really tried to do several different things to try and recreate the issue. but for the life of me, I couldn't get it to happen again. It held steady at 13.8- 14.2v. I tried with the lights on, air conditioning on high, heater on high, interior light on, stereo on....everything off.....lol. I tried everything, it stayed right where it should have been...UGH.

I have a battery/alternator tester, but the load part doesn't work. I'll go in the morning and try another battery and have mine load tested.

Thanks guys, for the help, it really is appreciated even if I didn't sound grateful prior.

minibike132 · December 11, 2009

It's in the low 20's/high teens at night and mid/high 30's during the day. I wondered if the temp could be an issue also, but sometimes it's fine, it's very difficult to trouble shoot.

So this after noon I went out and really tried to do several different things to try and recreate the issue. but for the life of me, I couldn't get it to happen again. It held steady at 13.8- 14.2v. I tried with the lights on, air conditioning on high, heater on high, interior light on, stereo on....everything off.....lol. I tried everything, it stayed right where it should have been...UGH.

AAAAHHHH I was under the impression that this is constantly charging at 15.5v. If your vehicle does have the electrical power management system it is perfectly normal for it to charge that high under some conditions. Lots of things go into the calculation of how high the duty cycle should be on the field current. 90% commanded duty cycle=15.5volt output.

The system determines state of charge at initial key on and uses alot of inputs to decide which charging mode should be taking place. Air temp has alot to do with it, the colder it gets the more charge you are going to get. Alot of other things are taken into account here.

If you are only hitting that level sometimes I would say it is most likely normal, if it is constant then there is a problem. It wouldn't hurt to have the battery tested anyway. If you get it tested get it LOAD tested. Don't go to the parts store where they have that crappy hand held electronc load simulator tester. It's garbage and is wrong better then 50% of the time.

minibike132 · December 11, 2009

I don't post documents here but a quick search found the charging circuit description HERE if you are interested in how it works. Search the page for document id 1467477.

EDIT: after reading it they only posted about 3/4 of the whole circuit description but you are getting most of it there.