last week my ses light came on with the code p0543. about four days later my truck won't start. I jumped the truck and got the batteries tested to find out that one battery was bad and it was only a 650 watt battery ( my other one was a 800 watt) thinking that the battery wasn't strong enough I replaced only the small bad one. two days later the truck was died again. checked the alternator and it was fine, started checking fuses and only found one fuse that is drawing alot of volts, the atc fuse isn't blown but put a meter to it and its drawing 9.25 volts. also want to know if the intake air heater circuit a open can kill the battery? This is my first diesel and first thread any help would be great. Thanks.

A weak battery feeds off the strong one. They should be replaced in pairs. If you are only seeing 9.5 volts, that's too low.

both batteries are bad. but before i get new one i want to find out if that code p0543 can drain my batteries.

It would be nice if you type in the vehicle parameters you are wanting help for. year,make ,model and other info in your signature. Yes, the glow plug or intake heater relay could be stuck and drawing down your batteries. Charlie

sorry 2002 silverado 2500 ext cab, Long bed, 6.6 turbo diesel, 4x4 with 249,000 miles, allison trans. no after market stuff yet.