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Best to have the batteries and the charging circuit load tested. You can get that done for free at most auto parts stores. Then upon that you know what to replace.
Found the problem!! Loose cable on the back of the alternator!! tightened it up and ALL is good!!
Thanks for the replies and hope that my fix works for someone else!
My battery indicator light came on when I was driving home tonight. Same behavior as the OP, comes on 5-10 sec after startup. This is a 2008 F250 SupCrew 6.4 Lariat (job 1, I believe). Funny, I was already planning to stop at the dealer to have the original factory drivers door keypad code read out b/c I bought this truck used about a month ago and can't find that code anywhere...so I asked them to check the batteries/alternator real quick while they had it. Nothing about the truck is acting out of the ordinary except that light being on. The battery and alternator tested good at the dealership and good again when I stopped at AutoZone closer to home...so I'm not quite sure what's going on here. I'll check that alternator wire in the morning when the engine compartment is a little cooler and we'll see what that yields.
I decided it may be cool enough so I squeezed my arm down there and I can only feel the one cable on the back of the alternator, and that seems pretty tight. I think that's a ring style connector and it doesn't budge when I tried to wiggle it back and forth...so that doesn't appear to be the issue. I'm the kind of person who likes to take care of my own problems...I guess we all are, otherwise what would we be doing on here? What else could this be?
This is pretty strange, but I think I've got a bad alternator here. Negative terminals disconnected on both batteries, they run 13.69 and 13.70 volts cold. When I hook them up, turn up the inside blower to hi, turn on the headlights, and go to start the engine...the voltage dips down to about 10.6 volts, I think (not entirely sure here b/c it's hard to capture that voltage for the 1 whole second it takes someone to start it up while I'm holding the meter).
Immediately after it's started, and for about a minute, the voltage reads right at about 12 volts. Then after a minute or so it jumps up to about 12.75. Then I check the voltage after driving around for a few minutes and the it's reading 14.05 with the engine still running. So I decide to take it up to O'Reilly and kill the engine before I go in. He hooks up his tester and tells me to start it up. As was the case earlier, the initial voltage sits at around 12v and the tester says regulator failed and diode failed. I think this is a single alternator system...passengers side right next to the wheel well. Where would the other one be if it had another? It does seem like I can smell a very faint electrical smell when I pop the hood, but can't really smell it any more after a few seconds.
The O'Reilly guy didn't really want to hook up the OBDII scanner since there was no CEL on, but I asked him to do anyway. Low and behold we found P0625 for "generator field low" and P373 for "brake switch low current". I think I'm remembering the codes right, and the verbiage is close but probably not exact.
Somewhere on here I read someone post that it's normal for the alternator to only start putting out higher voltage (14+ volts) a minute or so after the engine is started. Now I admit don't know much about diesels yet as this is my first one and I've only had it about a month...much less the F250 itself. That said, I've never heard of any other automobile designed to work like that and the gent at Autozone insists the alt should supply the full 14+ volts immediately upon startup...so that is one area that's a little unclear to me right now. The other thing I'm hoping to confirm is that the alternator is in fact bad and at the same time understand what would cause the alternator to behave like this.
To sum it up...
Is it truly normal for the voltage to kick up to 14+ only after a minute or so?
Is the alternator bad here...and if so, what's causing the voltage to move around like this?
My truck is the same...after initial start up it puts out around 12 v for the first min or so....This is because the glow plugs are still cycling if I remember what I read somewhere correctly.
Got the front pass side wheel removed and saw this axle seal or cover that is no longer intact. I wasn't really planning to tear this down right now, I just removed the wheel so I could get to the alternator from inside the wheel well. Not sure what this seal/cover is called, or if I should replace it now while I've got the wheel off. There are a few other things going on with the truck that should probably take priority before I go fixing anything that isn't quite as critical as a small coolant leak or a bad drivers blend door actuator. If I ignore this for now is it going to back and bite me in the ****, i.e. like take out the axle and/or differential? I took several pictures to hopefully show what I'm talking about. In the last pic (I think) it shows some rust on the axle inside. How serious is this?
That is your axle dust seal.....they pretty much all go like this after some time. There's a revised part to replace these with that lasts a bit longer. To replace this you'll also have to replace your knuckle seal and wheel bearing/hub o ring in order to maintain ESOF operation, as they are one time use seals, and when removing the axle to get to this dust seal are damaged. Unless you're going through a lot of deep mud or water you won't hurt anything really if this seal is busted like it is. You can try and seat it back in without taking anything apart...but if you manage to get it re-seated it is more then likely going to pop out again. Most guys don't really worry about this seal to much.
i have been having this issue, battery light came on and dash went out and on several times , i put battery tester on and batteries and they test ok, but the charging system is overcharging, i took the wire off the battery positive post that leads to back of alternator and it read 16.6v ... i changed out alternator, now with new alternator its reading 13.5-14v but as soon as i plug in the voltage regulator plug in on side of alternator the voltage jumps to 15.5-15.9v
is this a bad alternator or something else, could there be something wrong with this pigtail plug..
My truck is the same...after initial start up it puts out around 12 v for the first min or so....This is because the glow plugs are still cycling if I remember what I read somewhere correctly.
I learned in my case the rectifier is starting to go out on the alt. Voltage eventually comes up to 14v as the alt warms up. If I hadn't taken it off and sent it in when I did it would have taken out the stator and some other alternator internals. This is coming from a friend of the family who's livelihood has been repairing alternators, starters, and generators for 30+ years. A lot of the things that come out of his shop get some nice high temp paint, so I guess I'll see if he has any Ford blue...I'd be surprised if he didn't. Glad I didn't put this off.
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