Low voltage warning

Had same issue with 09 cascadia voltimeter readings low or zero the system alternator is charging batteries but warning buzzer on .ended up being loose connection or harnes goin to fuse box located driver side undru the hood wich is mounted on the plastic fender and gets a lot of vibration. Grease all fuses and push the whole harness in from bottom of fuse box. Hope this helps you. It fixed me up . Also voltige was going up and down

 

Hi what should the voltage be around with lights and accessories turned on!

 

Engine speed spinning Alternator determines that. Minus power drain of everything electrical on the truck.

Batteries like to be around 12.6 volts resting and ready to crank a engine when everything off. You need a minimum of 10 volts to keep computer networking and so forth on the truck up and running. Below 10 volts it's going to brick.

Alternators tend to charge perhaps around 14.3 or so. Whats left minus the sum total of everything drawing on it electrially goes to maintain the batteries.

Thus, you go back to basics in a shop. You load test the batteries themselves. If they pass then the batteries are good. If they fail load testing, then your next problem is retail three to four batteries virgin to purchase with the big enough CCA and capacity to fit the application specific heavy truck work. (Deep Cycle Marine Batteries, they will go out fighting to feed a stubborn engine.)

Sometimes Alternators die. When they do burn up, you get a red light and your voltage falls down to just above 10 volts. Turn off all electrical items not immediately needed. Get yourself to a shop big enough to diagnose and fix the problem at the root cause. There is a limited time before your entire truck bricks. This being winter it's really unwelcome.

Ive had alternators go bad, batteries go bad, electrial harnesses go bad and all sorts of amazing things go bad around a previously reliable strong 18 wheeler tractor. It costs a bunch of money really fast to chase down and isolate the gremlin munching inside your tractor electrically.

 

An alternator should be able to maintain battery voltage plus 1/2 volt with ALL accessories on.

13.1

That's what was taught in class and that procedure may have changed since I was taught in the late 80's. When external voltage regulators were still in existence and the internal regulator was the new technology.

Back then. 13.6 was about the weakest sign it was starting to go out.
A good alternator was 13.7+

There is a alternator draw test. But I don't remember the procedure. It was never used in my wrenching days.
IIRC. Full alternator amperage at 11 volts minimum. 15 seconds draw. You'd use the same machine used for testing batteries.

Back then. Alternators weren't quite as powerful as they are today.

 

What is Low Voltage disconnect ? On freightliner 2003

 

What is Low Voltage disconnect? On freightliner 2003

 

Does the warning stay on or is it just when you are starting it?

 

Battery low

 

Its load shedding. Probably a draw on the system or a bad battery.