The same thing happened to me. After a lot of frustration, it was a bad connection inside the drivers side positive terminal. Just like Old Smoky said.

The power to the truck (and naturally, the ecm) comes from the drivers side battery. However, the alternator sends charging voltage to the passenger side battery. If a connection goes bad, the charge voltage never reaches any of the rest of the truck. The ecm thinks the batteries are getting low, so it tells the alternator to start charging. The connection is bad so the charge voltage doesn't reach the ecm, so the ecm tells the alternator to work even harder. Mine was cranking over 18V to the pass battery but the drivers battery was down below 11V. The problem area in mine ended up being corrosion around the cross-bolt that goes through the positive terminal of the drivers side battery lead.

BTW all this happened a few days after I installed new batteries. Naturally, I went and raised a fuss at the battery place. They were very patient with me, and let me pull my truck in their bay until we figured out the problem - free of charge. I felt bad when I found out it was not their fault!

 

Nope, no PCM between 04 and early 07. All the controls were in the ECU. The charging is an engine function so its in the ECU.

Its possible the ECU was bad but I would definitely make sure what cause it to go bad is not still there. Connections on the battery posts are critical or the same thing will happen again. Pull 'em all, clean and apply grease or whatever your choice is where it is needed.

 

I had this happen as well. I believe it was just the connection, but at the time was under the 3/36 warranty, so I took it in. Apparently there was a TSB for it that called for reflashing the ECU and two new batteries. Cleaning the posts and tightening connections probably would've done the trick but I would've been stupid to turn down a new set of batteries.

 

This begs a question. I still have the OEM batteries. Everything seems fine in charging and starting, even -30F (recently), without the block heater plugged in. Hated to do that, but needed to move the truck.

Wonder how long those OEM batteries last? I'm at 6 years and two months.

 

my oem batteries will be 8 years old in june in my 2003, 167,000 and going strong

 

Kinda glad I stumbled upon this thread. Need some advice though.

Background: My stock batteries finally bit the dust and had to get new ones (bought new in early 2005). About a day after I put the new batteries in, I was on my way to work when the volt meter on the dash dropped to 8 volts and the Check Gauges light came on. Shut the truck off, restarted, and it cleared. It happened again about 15 min later, but made it to work. After work I stopped at Autozone down the street to check my alternator. When we opened the hood, one cap set had blown off and a bit of acid had blown out too. They wouldn't check anything and dismissed it as a bad battery. Drove over to the Napa where I bought the batteries. Ran their diagnostic tool and both batteries tested good, but it registered a "charging system problem". I figured it was the voltage regulator, and ordered a new alternator thinking the regulator was part of the alternator. I didn't realize until tonight while reading the Tech Manual that the Voltage is regulated by the ECM . I have the new Alternator in hand, but haven't installed it so I can potentially return it. For now I disconnected the negative terminal on the passenger side battery but am not sure that is the right thing to do.

Where direction do I go now? I can't afford a new ECM right now. Should I shoot into the dealership and see if they can flash it to reset it, or am I SOL? I did clean the posts and the clamps when I installed the batteries, as well as put some protectant on, but I'll dig a little deeper first to make sure all the connections are good.

Any advice would be appreciated.

 

Just found this post. I've been posting about the same issue in other sections. Truck is down, with batteries disconnected until I get all the info on where all to look. Afraid to hook it up before I do.

I've got a list of things to check:
1. Connections (mine were cleaned but now the passenger side + terminal is literally melted with holes). Should probably buy new.
2. Batteries - one fried but has been replaced. Both test good.
3. Alternator - not tested yet
4. ECM voltage - can it be tested with a volt meter directly, or would testing just at the batteries give the same readings? (would the reflash mentioned fix this?)
5. ..........


Anything else to add?

 

This happened to a friend of mine...
https://www.dieseltruckresource.com/...hlight=battery

 

Keep your old ECM......mine did the same and just needed a $90.00 reflash.