Charging system woes

My 2003 is having charging systems issues. I have the version of 2003 that does not have the 1.9 fuse for the alternator, there is battery voltage at the #3 (orange/ blue stripe) terminal of the alternator but with a fully charged battery it's only putting out the same 12.2ish volts at the BAT lug, I bought a reman alternator from Amazon, they swear they test, retest and triple test them six ways to Sunday before they send them out but with the new alternator installed its still not putting out. So unless I'm missing something the only thing left is: I was sent a faulty alternator, the wiring from the alternator plug to the PCM is faulty or the PCM itself is faulty. Because of my schedule it's hard for me to get into a shop to have the alternator tested, but I may have to do that, before I do that though I'd like to check the wiring. Does anyone know where exactly those connect to the PCM? Or is there something I have missed?
Also, this is a 227,000 mile truck but everything else works perfect, so if it is the PCM the portion controlling the alternator is the only thing wrong with it.

Recently went through this. I started with a battery but it warning light came on after a day. Then I replaced the alternator wiring harness that goes from the alt to the positive battery cable. Then I switched alternators with a Ford Motorcraft which eventually solved the problem. It should be noted I was having draining issues not just a light on. Is it just that the light is on or are you having draining issues as well? I see you mentioned a little weak of a battery but otherwise are the volts going down when it aired up, lights on, HVAC on etc? Mine was so in the end this is a car I picked up 2 weeks ago with 200K miles so I'm ok with having replaced the above parts for piece of mind.

06 Eddie, I'm not sure I'm following you, if your charging system is not charging for whatever reason, absolutely your battery will steadily drain, the more loads, the faster that will happen. So yes my volts are going down, but it's sitting in the garage till this problem is solved.

Sorry, to clarify some people report the "check charging system" light on with no symptoms. Was just asking if you had actual charging problems otherwise I'd suggest having the code cleared. The reason I used a motorcraft was people reporting even new alternators from local auto stores not being able to generate enough power. If you have a new alt and bat then try that alternator wiring harness. It's 40 bucks from Tasca parts.

Checked voltage directly at the BAT lug so the harness has been eliminated as a possibility.

Diagram attached.

Check continuity on each of the two wires at pins 1 & 2 connecting the alternator to the pcm once the pcm has been disconnected. If they show good the next step is to scope the signal from the pcm at pin 2.

stamp11127 said:

Diagram attached.

Check continuity on each of the two wires at pins 1 & 2 connecting the alternator to the pcm once the pcm has been disconnected. If they show good the next step is to scope the signal from the pcm at pin 2.

Click to expand...

Thank you for the response, I'm not following what you mean by "connecting the alternator to the pcm once the pcm has been disconnected." I think what your saying is to check the integrity of the 2 wires from the alternator socket to the PCM socket? My problem is I'm not sure where to probe on the PCM end, the diagram says 7 and 14, is there a pin out diagram for the PCM plugs? I'm curious too, when the alternator is receiving no signal at pin 2 does it simply default to no output?

I replaced my 2003 Expy alternator a few years ago (Advance Auto) before a 7K mile trip due to a noise (that I thought was alternator going bad but ended up being a bearing for serpentine belt). Drove out to BC & back with charging trouble light coming on occasionally (making me nervous) but otherwise OK. I never drove at night, only during the day. In the UP of Michigan the signs advise running with headlights on during the day so I did that and battery ran down stranding me in Munising. The guys at SKIPs AUTO REPAIR were busier than heck but somehow got me in and diagnosed bad alternator (low charging voltage) & repl'd alternator fixing problem. Brand new rebuilt alternator bad out of box! It was right on edge so all it took was turn headlights on and insufficient juice to maintain batt charge. They diagnosed it by measuring battery voltage at idle (12.2 V should be 13.5 or so) and it dropped voltage when headlights turned on. Also I think lights were a little dim (the ones on the Expy, not mine LOL)

Took bad alternator home (had to pay core fee) and took back to Advance Auto. Manager insisted it couldn't be bad and wouldn't do anything. Claimed they test them thoroughly etc. I wouldn't give up and kept talking (nicely but insistently) and eventually he gave me a $250 gift card.

The guys at Skips Auto are the BEST!!!!!

Check the continuity of the two wires between the alt & pcm. If you are lucky the problem is at the connector c192.

Without a signal from the pcm "telling" the voltage regulator to turn on and by how much, the alt stays off.

I am having a similar issue. This is an 03 Expedition EB. It has the 5.4 2wd with about 220K miles. Mine has been a few issues all at once. I fixed the stalling issue by replacing the unserviceable fuel pump relay in the fuse panel. That was fun. Recently, even before the stalling issue I had an intermittent "check charging system" light. I have checked and/or changed just about everything. Once upon a time I had this happen because of the 1 wire shorting out on the A/C accumulator tube. That was bout 3 years ago. I repaired the wire and replaced the Alternator. That fixed it. This time around I thought it might have been the harness again. I really knew better because the wire I repaired appeared to be fine. But, I have been working a lot of OT and the fastest fix seemed to be just to replace the harness in case there was something else going on that I couldn't see. Installed new harness and still no charging. They warrantied my alternator out. So I replaced it. Some reason they couldn't test my old one. Installed the new one and still not fixed. While the engine is running it slowly drops at the battery. So I started checking all contacts and wires. I even put on the old harness again. Somehow it started to charge again. Verified at the battery 14.2v. So, I put a full charge on the battery and my wife drove it for about a week. Then the stalling started. Repaired the fuel pump relay and threw it all together. Now runs fine but the charging issue is back. I moved the old harness around and it would start to charge again. When from 11.86v and dropping to charging. Jumped pretty quick to 12.6v and climbed. I let go of the harness (I was holding it at the fusible link) and it dropped again. I put the new harness back on and cleaned all of the connections. Especially the one that is under the battery tray. It actually appeared corroded. I cleaned the battery posts again. The main positive cable to the battery looked like it has a little corrosion in the connection between the wires and the cable end. It is the original and I wonder if I should peel back the shield and see if it is corroded further up the cable. I cleaned what I could see on the end. I put it all back together and it is still not charging. Is the C192 the connection under the battery tray? I remember seeing a link posted by stamp11127 with a lot of items to check. Including how to check voltage drop, which I had never done before. Everything pointed to the alt. But, I too am not sure where the connections are between the PCM and the alt. Or anything else I have missed. I normally have no issues repairing my own cars/trucks. I have been working on them for 30 years. I have rebuilt entire engines. I have taken on some jobs that I wish I had not, including replacing a mitsubitchy belt driven water pump on a Dodge mini van. I would have rather set it on fire. But, I finished and everything worked. All this to say I am truly stumped and do not want to have take this to anyone. Especially since the 1st thing they will likely say is replace the alternator. Surely I haven't gotten 2 bad alt's in a row. I am beginning to wonder if there was anything wrong with the 1st one. All of these have been from advanced auto.

Sorry for the book. But this has been going on for about 3 weeks total and I only have time this weekend due to the holiday.