Well, found a dead battery in my truck this morning, luckily I am off this weekend so there is plenty of time to address the issue. Not so luckily its supposed to rain all day but I guess thats just the way it is.

Anyways, does anybody know what a normal parasitic draw on these newer vehicles is supposed to be? Does the old wisdom of less than 50mA still apply? FWIW my truck is pretty simple, just a basic XLT although I have added an aftermarket radio headunit and a new headlight harness (both of which, would obvious be suspect first if a draw is found). Right now I'm charging the battery back up from 9.1v and will naturally have to test it later as well.

 

Should draw less than 50 mA after 40 minutes of inactivity. You MUST allow the battery saver to time out, otherwise you'll just waste time chasing ghosts.

 

Common, known causes of battery drain ...

• LEAVING THE KEY IN THE IGNITION. *TAKE IT OUT BEFORE LEAVING THE VEHICLE.
• leaving devices plugged-into the electrial recepticles. *they're ALWAYS hot.
• faulty ignition switch. *symptom - key is loose.
• faulty shift lever micro-switch. *does not register as being in P(ark).
• faulty door -closed- switch.
• the mirror cover on the passenger visor does not close causing the light to stay on.

Don't forget to follow the instructions in the owner's manual regarding changing and/or the battery and the need to rest the BMS (Battery Management System).*NOTE: FoMoCo dealership service can reset the BMS using their IDS (Intergrated Diagnostic System) negating the eight hours of vehicle sleep time requirement.

(owner's manual) Don't have one -OR- would like a digital, searchable desktop document?

 

:thumbsup: Just waiting for the charger to finish, then a quick check for parasitic draw, parts store for a load test and regroup from there.

 

So a bit of an update, and hoping for some advice. Tested out and the parasitic draw dropped to 40ma after about 10 minutes. Old battery was 8 years old, load tested fine but figured this is a good excuse to replace it before winter. New battery in for about two weeks now. Truck is a "daily driver" but does not get driven every day. Sometimes 7 days a week sometimes it will sit for 4-5 days without moving. Recently sat for about 2 days without moving. Started it up two days ago and it was a little slow to crank but started fine later that evening. This morning the battery is completely dead. This is the new battery (which I had fully charged on my Shumaher SC1200a prior to installing 2 weeks ago.

Clearly, to me, there must be a parasitic draw at some point. But if I am measuring only 40ma after 10min then what the heck is going on? Do the computers power on at some point AFTER that?

gDMJoe, thank you for the brain storming but I don't believe any of these are the culprits although I do need to double check the vanity mirrors.

Also I just noticed the other day that the truck won't shift into 4hi or 4lo at all. Not in D, N or P and not while stopped or rolling. Clearly the suspicion would be the solenoid but could this be related?

 

FORScan is showing "0.00" in BAT_CURRENT, Amper shortly after engine off key off doors closed no activity. This would agree with earlier measurements of <50ma draw under there conditions. Watching a youtube where a guy found a >3A draw which began HOURS after shutdown which makes me wonder. He found the alternator was developing the draw without energizing any other modules which I just don't understand...

 

I watched a youtube of a mechanic chasing down a parasitic draw. 200mA dropped to 50mA afters 40mins but around the 2 hour mark it jumped up to 3A. When this happened he noticed the alternator was hot....it was drawing the current. The solution was a new alternator which surprised me (it was a 2010 truck with 5.4L). I guess the two key take aways are.....you need to data log to catch it, when it is happening you need to see what is drawing the juice.

Trucks are getting way to clever.

 

Alright well I might have found the problem. Seeing 31vac (yes, volts alternating current) across the battery posts with the engine running. Everywhere I look it should be under one volt ac. This strongly leads me to suspect alternator problems with the diodes in the rectifier. Of course, it can't be that simple. Compared to a known good 5.0L coyote F150 its pretty close. That truck shows 28vac and sits for 4-10 days between uses with no problems.