Help!! My 2009 F-350 6.4L wont start all of a sudden. I bought it about 6 months ago and haven't had a problem since, but all of the sudden it won't start.
I've tested both batteries with a Voltmeter and they're both reading 12.4V. when the truck is off. Is this a normal reading for a battery?
When I turn the key to the ON position I get a two messages on the dashboard. 1) "check brake system" and 2) "check brake module" and the security light also flashes.

The weird thing is when I jump start the truck with my other car, it starts right up.. After it starts both batteries read about 14v.

Do I have bad batteries? I thought 12.4V should be plenty of juice to start the truck.. Can anyone tell me if they need to be replaced? Also, why I'm I getting the brake system error messages when the truck won't start?
As of now, the only way I can start my truck is with a jump

Any info will help.
thanks

 

I have seen mention of this message appearing before and most have indicated that one of the batteries was failing. I know you have mentioned that you tested voltage and they were testing over 12 volts.

But just cause a battery indicated it has the voltage doesn't mean the battery has the amperage need to help crank the truck over, which is why batteries indicate the cold cranking amp, Your best bet would be to pull both batteries out of the truck and take them to an automotive store and asking them to test both batteries for you, they will check the voltage but they will also test that batteries amperage.

The powerstroke engines by nature have always used a dual battery set up because of the amount of juice the truck needs at start up because of the injector buzz before your crank the engine etc.

If you do need a new battery , you should replace both batteries at the same time, not just one, if one of your old batteries is good and one is bad, you can always hang onto the other battery for the shop the wifes car etc, but when it comes to diesel its recommended you replace them both at the same time.

I know you said you got the two brake messages, but I dont think that is your actual problem or the truck would turn over, because the two brake messages in my mind would lead me to think of a problem more in line with the ABS module. I believe rather the batteries are the real problem and the brake messages are more of a symptom of the battery issue.

You could try looking up the date on the batteries but that could be hit and miss. Diesel's produce a lot of heat and they need a lot of juice to crank and then turn over adn the heat that a diesels engine produces doesnt do the batteries any favors over time either

 

Thanks Pocketlint for the insight on how powerstokes need lots of juice to crank. I guess 12.4v isn’t enough. I hope the problem is what you suggest (shot batteries) and nothing more serious.
I will take both batteries to an auto store first thing tomorrow and get them checked. I’ll report back..

I forgot to mention that this “no start” issue started happening after I installed my airbags in the truck. I installed the bags about 2 months ago. When I installed the airbags, I hooked up the power straight to the battery instead of the ignition wire. Is it possible for this to be the culprit of my battery draining over time? Maybe there is a draw from the airbags connection? I’ve removed the power from the airbags to the battery for now to see if the battery will hold charge after I get them fully charged and tested tomorrow.

 

I wouldn’t think that the airbags are draining the batteries just because they aren’t all that low; if you had a constant drain, you’d probably have readings much lower than 12.4. If they’re a few years old, that’s really not an abnormal reading.

Since the problems began after you installed your airbags, try unhooking the airbags from everything (including the battery) and see if your starting issues go away.

 

Seville is right you need to check the airbags first. If the airbags are seeing constant power that could be your issue. I would take Seville's advice and go from there

 

also check the brake switch, brake switch wire, etc