I am brand new to this group as the proud owner of a 2012 F250 6.7L. I've owned it for two months and it had driven perfectly up until a little over a week ago. I got the dreaded downhill traction warning and then I started losing all power to the dash as it was now into limp mode. I first tried the fix with the emergency brake buy unplugging and replugging the connection at the brake. Also detached where it was connected to the brake and tied it away (as recommended by other threads) and used electrical cleaner on the plugs. I was still having trouble so gave in and bought an OBDII scanner. When I scanned the truck, I got a high voltage reading on both the system and the ABS. Tested the alternator and the alternator was bad. It looked to still be the factory alternator and I thought possibly the voltage regulator was having issues. The leads off of the batteries were reading just over 17 volts.

Bought a new alternator. I could not tell if the factory alternator was a 150 amp or 200 amp, but both matched the vehicle. I'm going to be hauling a trailer with the truck with several lights and might add some other stuff in the future so went with the 200 amp alternator. Hopefully that wasn't a mistake. Installed the alternator and started the truck and everything looked great for about 5 minutes then the battery light came on, then traction control, flickering of lights, and back to limp mode. I attached the scanner and got the following codes on the ABS - B11E8-17 - (ABS) Power Supply - Circuit Voltage above Threshold, C0049-7B Brake Fluid - Low Fluid Level. The brake fluid level looks good from visual inspection. I checked the new alternator and it was testing just over 14 volts and was declared good. Batteries tested good.

I cleared the faults using the reader and they came back about a minute later. I'm wondering if the bad alternator's higher voltage fried the ABS module? Anyone have any other ideas of what could be causing this? I was going to do a battery reset later this morning to see if that helps to clear out the faults but I'm not hopeful that will fix the issue. If anyone has any ideas they would be greatly appreciated.

 

You need to really rule out the charging system. I would hook up your DVOM on the alternator and do a jiggle test. It sounds like you have something going on with the alternator wiring, like the exciter is grounding. If you are still getting 17 volts, it has to be coming from somewhere. The batteries aren't making extra voltage, the BCM isn't making its own voltage without a transformer in there somewhere...and there isn't one, and the BCM will drive the alternators to their specifications based upon how it's monitoring the system. I don't think the BCM will be capable of driving the alternator beyond 14.7V or so. See my reasoning here?

 

in simple terms...

there are two modes of operation in the alternator/pcm.

SMART and Dumb

SMART mode is controlled by the PCM and the voltage will vary from 14.75 to 14 volts. the variation is due to battery state of charge.

dumb mode is an alternator operating with out PCM control. it is typically 13.75 volts.

the 6.7 has some gremlins in it when it comes to the charging system. google youtube AROD battery charging error / light, etc. Arod will walk you thru a wire that internally fails...when it fails the PCM can not sense the battery voltage on pin 1 while at the same time has a connection on pin 2 and 3. PCM goes hay wire and you get greater than 15Vs. the fix in this case is to install a by pass wire...which is covered in the video.


this is a tricky situation. I had the same problem along with "service charging system now" idiot light. I knew about the wire problem and tried to test for it....since I got voltage on all pins...I rules out the wire problem....problem remained...took it into the dealer...and they said they replaced the wire and all was good.

 

Did you end up getting anywhere with this issue? My 2013 6.7 is having the same exact problem.

 

I would also look at your batteries. If they are 3 years old or older just replace them. These trucks are very sensitive to voltage drop. Just a 1/2 volt drop could cause issues. If your alternator tests bad your batteries are bad as well. A bad alternator will ether overcharge a battery or drain all the life out of them. To see if your batteries have been overcharged place your hand on the side of the battery. If the case has a buldge in it no matter how slight that battery is junk. You have to replace both batteries at the same time. Sorry it's a battery rule.