Scotty my 2007 GMC 4x4 5.7L Flex fuel engine 4 speed automatic approximately 60k miles. Frame was changed 2010 when idiot hit me so hard in front right quarter frame was bent in back. $21k repairs.
Some times at high speed and rpm "service charging system" appears on dash info and volts as per dash gauge drops to around 9 volts. Truck runs fine and voltage slowly comes back up to around 13-14 volts but message remains. When I turn vehicle off and restart later the trouble message is gone and charging system acts normal. I already changed the charging sensor on the ground cables and things appeared to be fixed...it just happened again. The vehicle is in great shape except for the charging troubles.
I did add a second battery when I installed a Warn Transformer kit on my truck and had the extra cable from the kit, and would be using a winch. Would the second battery affect the charging system?
Truck never seems as if it was going to stop running just would like to know what's going on before I do get stuck while pulling a 30+ foot trailer. Paid $30k cash for truck from Crown Buick GMC Metairie, La. new.(mega overtime ma bell after Katrina) {black}:idontknow:
correction 5.3 L Flex fuel
You had a second battery that could really mess up the charging system and confuse it if I were you I would disconnect the second battery then load test the alternator check the wiring if it's okay leave it with only one battery. Pray it's that easy of a fix
Thanks Scotty I'll do that tomorrow.
Did road test with the single battery. Don't have equipment for load test.
Tested with hard acceleration high rpm, voltage dropped momentarily, came back up with normal driving. Service battery charging system warning did NOT come on this time. No codes or messages of anytime.
I heard through grape vine the voltage drop under these conditions is a function of the truck system...I'm not inclined to believe that. Is that true or internet BS?
I will keep you, ya'll updated as things move along.
Thanks Scotty!
battery dealers and some part stores (Autozone) will test your electrical system for free
the computer only senses one battery (via the sensor you mentioned)
The second battery is in parrelel and the ground for both go through the sensor on the stock ground wire. After wreck the mechanics install the battery in the back of the engine compartment on passenger side. I took the advantage of the battery space and ran positive and negative cables to the positive and negative terminals on the factory battery. Any draw on either battery will go through the cable in the sensor.
then maybe the computer is expecting one battery, and is confused when it has to charge two of them. Do what Scotty says and unhook it. See if the problem goes away.
Took the extra battery out today. Have a road trip coming up moving sold house...Hurricanes permitting
Will keep ya'll updated.
No, what you heard about voltage is not internet baloney. Modern vehicles have intelligent charging systems that modulate charging voltage, and loads, according to conditions. And it does help batteries last longer.
This is why hooking up a second battery isn't such a simple matter. Some people use charge controllers for this reason.
what I do know for sure, is that's not the way GM recommends hooking up an auxiliary battery. To quote from an upfitter manual
Battery isolation can be done in a number of ways. In this section we show you two ways that GM does it. On medium duty trucks we have a diode isolator component that places in line diodes in the battery charge lead going to the alternators. On CK trucks we have a relay isolation scheme.
You can find more technical details and diagrams on gmupfitter.com
Hey Joe thanks for the info about GM up fitters. Just what I had been looking for. They'll be closed for 2 weeks July 5th(my luck just in time).
I will be using it a lot, looking to upgrade other things on the truck.
their offices are closed, but you can still download info from their website. Click on Body Builder Manuals and look up your vehicle.