Low voltage warning

could be a short in one of the batteries, would start by testing them,before i spent alot of money. lots of luck

 

It could be any number of things but I would start with the basics. First, get a good multimeter and check the voltage at the back of the alternator with the truck running to be sure your alternator is charging. You should have between 13.8 and 14.2 volts with the engine running and no load of the system, meaning your lights and other stuff off. Next check all the battery connections to be sure they are tight, clean, and not damaged. I have seen the ring ends crack and though they appear tight if you touch them they will break off. Be sure to follow the wiring all the way back to the starter to check that end as well. If the alternator is charging and you don't find a bad connection then you will need to load test your batteries. To do this you will need a load tester which can be bought at any auto parts store. Make sure your batteries are fully charged then disconnect them completely and test one at a time. If you find a bad battery I suggest replacing them all at the same time, they work best when closely matched.

Another thing that may be causing low voltage warning and hard starting is if you are using an inverter or other accessories with the engine off, especially if the batteries are a little weak or if the truck only has two or three batteries, which is common in former fleet trucks to save money.

 

A decent multimeter to check voltage is only about $20 at Lowes or Home Depot and a battery load tester is about the same at Napa or Harbor Freight. Owning a truck will be much more profitable if you start building a good tool kit and learning how to use them. Buying some basic test equipment and learning how to use it will be much cheaper than running to a shop or dealer every time something pops up. The dealer is going to nail you at least an hour just to look at it, that will cost more than double what the tools to do it yourself would cost, and you will have the tools for the next time. These are the little things that will make you a more successful owner operator.

 

a decent 500 amp battery tester is $40 at harborfreight. a volt meter is $4.

and you want a voltage check at the alternator WITH ALL ACCESSORIES RUNNING. not off. and a voltage check at the batteries.

most alternators will pass if nothing is on. but it won't help you at night in a storm if it can't keep up with everything running.

BUT, you can also use the battery tester to also test the alternator.

anyone don't beleive that. you can do a google yourself for a link on instructions.

 

if u suggest to get bad connections crank engine with starter and check all terminals and connections. bad connection is usually hot.

to use dash voltmeter is not the good idea, becouse to be sure batteries are bad u need to check voltage in bettery box on battery terminals.

I'd use clampmeter to check current, becouse bad starter is the thing that may overload batteriess for so notisable voltage drop

 

If you Google anything with testing a charging system, you will always get one source saying one thing, and another source saying something quite different.
If you have to Google anything, chances are a person isn't quite sure about it to begin with.
I don't need to verify items in your post with Google,, I'm familiar with the process thru years of hands-on experience.

Your highlighted "WITH ALL ACCESSORIES RUNNING" is not correct by itself. You must state some important exclusions and conditions with it.
If testing WITH ALL ACCESSORIES RUNNING, then the engine/alternator must be operated at much greater than the typical 600-700 RPM engine idle speed.
Even good alternators will "fail" the test at only idle speed. You should be at at least 1,200 RPM, minimum, or more.

Also NOT ALL accessories should be on. Limited use "high draw" accessories like electric element heaters/defoggers, seat heaters, etc, should not be on.
Only the standard electrical items, such as headlights, running lights, heater blower fan, etc should be on.
As for a $4 voltmeter... I have yet to have seen one with any accuracy to it's "readings".

 

Did you leave the fridge on? A lot fo used trucks have batt problems and they need to be replaced. While sitting on the lot things like the fridge are left on, then it gets started, driven for a short trip and shur down. Constantly being drained and not charged is bad for batts. Give it a good run for a day and see if the problems goes away. If not get ur batts tested. The fl dealer charges like 55 bucks to test um.

 

delco-remy, motorcraft, and mopar would tell you otherwise.

a good charging system will be able to run ALL accessories. and maintain a 1/2 volt for the battery.

a fully charged battery is considered 12.6 volts. plus 1/2 volt. leaves the alternator putting out a minimum of 13.1 volts.

my 97 cavalier puts out 13.9 volts at 1000 idle. my 94 suzuki bike puts out 14.2 at 900 idle. and the lights are always on. my kenworth puts out 14.2 at 800 idle.
ALL ACCESSORIES RUNNING. limited or not. NO EXCEPTIONS.

them $4 voltmeters at harborfreight are very reliable. and as accurate as my old $200 meter that iincludes dwell for points. i bought it back in 88. when i first became a emissions mechanic.

i just saved you the hassle of google. becuase i went to those delco-remy, motorcraft, and mopar classes. and since i mechaniced for 12 years. i'm pretty sure what I'M talking about.