I got in my truck last Thursday to go to an appointment and a half a block down the road the battery light came on then it said to check charging system so I turned around to go back home and by the time that I got to my driveway it said to check the braking system also. I brought it to O'rileys and they put it on their computer and told me that the alternator checked out but the battery was bad and being it was the original battery I bought a new one. After putting in the new battery and starting my truck it gave me the same warning so I went back to O'rileys and they checked it again and it gave us these codes P0620-Generator Control Circuit Malfunction, P0625-Generator Field / F Terminal Circuit Low, 40433-Invalid Data Received From Control Module. At this point they tell me that my alternator is bad so I go home and remove it and in the process I find that 1 of the wires on the back plug is corroded and falls off the plug during the alternator removal. I take it to O'rileys and they test the alternator and tell me that it is fine so I buy the plug go home and put it all back together with the new plug so when I'm all done and start the truck I get the same battery warning light. I spoke to the dealer and they want to diagnose the electrical problem and to me that means $1000. Any advise would be most welcome.

Wade

 

bad or corroded wires are always a possibility... That being said, your battery was 8 years old and really needed replaced... The alternator is same age, and how many miles on it ? I believe an "average' alternator or starter lasts about 175K miles... some more, some less... Auto Store is not the best place to check out an alternator as they get a snap shot in time and you may have random problem. What I would do is measure the battery voltage with motor off.. Should be about 12.5 volts maybe a little more...Then start the truck and it should jump to 14 volts ( little more). If not, then the alternator or wires to it are bad.

 

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?

 

I was getting the same check battery light on my truck when I bought it used. the battery was charging correctly just the warning message would always appear. took it into a local repair shop (not Ford dealer) for some other items. they found that one of the wire harnesses had been scraped bare causing the warning light to come on. they made repairs and the light has never come on again. they said it was a sensor lead to tell the computer that the alt was charging correctly. I am not sure what harness it was but the pic they showed me it looked like one of the main harness bundles. maybe have look to see if you can see any harness that got scraped. they found it pretty quickly once they looked for it.

hope that works for you.

 

It has 104,000 miles on it, I will check the voltage on it after work tomorrow and being I have a back up vehicle the BMS time frame will be covered. I will let you know how it goes. Thanks for advise its most appreciated.

 

Ok so its at 12.5 volts without it running and jumps to 13.5 volts when I start it. looks like I will start with a new/reconditioned alternator and hope that that resolves it. Thanks for the advise.

 

I would look into it more. I can't find the page i was reading but i seem to remember these trucks have an odd cycle where they will charge at 14.6 ish volts and maintain a charge 13.5ish and not charge when they do not need it. something that helps them with epa regulations.