Hello All. In need of some help. Truck (2018 6.7) has been sitting for a few weeks, fired it right up then the dash and all controls when dark. Scanned for codes had all kinds come up related to charging system. I let the truck idle for a bit to charge the batteries still acting up after 5 minutes of idle it was also putting out 17V. I figure perhaps the batteries are low so I gave them a full charge overnight, put a load test they seem to all check out okay.

Hooked everything back up, cleaned the terminals, cleared the codes and now I'm getting a P0625 Generator Field Terminal circuit low from the PCM with the battery indicator light on. The truck has duel alternators only 50k miles on the truck. The charge voltage was initially 17+volts when dark (prior to the batteries being charged). Now the batteries are sitting at 12.9V EO and running the truck is charging at 14.5V. So everything seems to be working as it should.

Puzzled on this one if I have one of the alternators going down or a bad ground or ? Everything was working fine when the truck was last in operation. Any help / suggestions would be much appreciated.

 

unhook both batteries.

Then check both alternator terminals and grounds.

If all ok, try again.

It sounds like one is not working (alternators).
anywhere from 13.9 to around 14.5 volts is what my alternators always read at. But just one alternator can do that amount.

 

Thanks Senix. I checked both alternators from the batteries to the terminals both seem to be working. I am getting higher volts - above 15 so definitely an overcharge situation.

I also checked each red wire (#3 wire) at the alternator, each both getting 12V from the battery - okay.

I'm trying to find the PCM terminal coding for this truck so I can check each wire going to the PCM from the alternators - might be harder to find with the dual alternator set up. If anyone could share or know where I could locate the wiring diagram it would be much appreciated. I believe is the C1232B connector?

So far everything I'm finding relates more to a wire being shorted causing the overcharge vs a bad alternator(s). I do live in Canada where corrosion is a problem and these wiring harnesses apparently are an issue for not being well protected as they loop around the underside of the motor to get to the PCM.

 

A-rod on youtube (PTT is what I think he calls it, powerstroke tech talk) has a video about this and how folks replace alt & this & that when the problem is a wire in the harness under the engine.
I'm not saying this is your problem but if you can find the video he points out which wire to look for.
If I wasn't such a computer dumb azz I'd try to do the link stuff hahaha

 

Thanks, Yes I have seen that video, very helpful. I just need the PCM schematic for the twin alternators to see if any of the 3 wires are shorted. That vid was on a single Alt. I have watched and read everything from rodents eating wires to bad alternator to wires being chaffed / corroded in 3 different areas around the base of the Eng.

Originally when I first started the truck the voltage spiked to 17V (assuming the batteries were low) then everything in the truck shut down (audio, running boards, dash, lights etc.). The eng. would run but nothing worked, couldn't even put the truck in drive. I guess this is a fail safe to protect the electronics. After charging the batteries and trying again next day the command for power is a lot less now everything is working. Battery light still on with the "service charging system now" message about 30 seconds after clearing the codes.

Not sure if there is an easy way to confirm if the Alts are okay? Going to try and disconnect one at a time with all systems on and see if I get any change in voltage that might indicate one is bad. From what I have read the main alternator does all the lifting with the secondary for additional load. If one goes down it can mess up the duty cycle triggering the code.

 

 

I had the service charging system error…the problem was the wire in a rods battery light fix video.

also, there could be some corrosion from battery gas so if you needed a reason to swap to agm, this might be it.

 

Great video thankyou. Would like to know if those same PCM locations apply for dual alternator set up.

 

I believe this is it. There is 2 additional locations on the PCM to check.

 

Well just a quick update. I originally checked the Alt. couplers for power both checked out okay (#1 loc). Chased wires around the pinch point areas didn't see anything concerning. The Drivers side is almost impossible to get at. Checked the Genmon 1 and 2 readings at Idle and at 3k where the 1st Alt was running around 50% and the 2nd 5%. Tested again under load - ok. The VPWR was showing 14.96. The GenVDSD for both 1 and 2 were within 0.5 of the VPWR so it wasn't looking like a PCM wire problem.

Checked resistance between the Alts and ground - ok. Checked all 4 wires (Gen RC and Gen1) going to the PCM everything checked out okay ~2 ohms. The last thing to check was the test light power at #1 on the Alt couplers. The 2nd Alt was fine the first Alt failed (no illumination). Showed 12.9V as soon as any load was applied it went to 0.

So looks like I'm chasing the power wire yellow/red back to the BJB from the main Atl. The 10A fuse checked out okay BJB which I thought should have blown if there was a ground short. So start taking stuff apart tonight I guess to find out why I'm not getting full power to the main. Anybody have any experiences with this wire and provide any tips it would be much appreciated.

Btw whoever designed the wire harness for this motor should be fired. What a stupid way to save a few cents by not protecting these wires and designing in 90 degree pinch points. I'll probably go through all the wiring while I have it apart and add protective covering to any of the prone pinch areas so this doesn't happen again.

 

Hello All, need some recommendations. I have traced the short to somewhere around the power steering unit. I've pulled the fender liner it still doesn't look easy to get at. Really don't want to take more things apart.

Few options
1) Keep pulling things apart till I locate the short splice and fix.
2) Run a separate wire splicing into the yellow/red from the A/C location running it all the way to the Main Alternator overtop of the existing harness. Not sure how else to do it? I believe this is what most would do. Just don't like the long term prospects of the wire being somewhat unprotected.
3) Splice in a wire from the Alt connector to the B terminal (6" 20 gauge fused with eyelet). Which would be the easiest option just not sure on the risk??

Any experiences or suggestions would be much appreciated. Btw Ford won't cover this failure under the Powertrain warranty, not sure how a harness is a wearable item ffs.

 

Latest update. Sourced the broken wire on the Drivers side right at the power steering pump. What a brutal job to get in and get access to the harness.

Attached are some pics. Hope this helps anyone that has a similar issue. The one thing that did surprise me is how tight all the tie wraps holding the harness down. Basically the harness can't move within the molded protectors. Some seemed extremely tight which is what i'm thinking caused the wire to pull apart. I'm going to put a protective sleeve overtop of these wires so I don't run into this again. Apparently this is still a problem on late model trucks.

Note the protector under the power steering housing is a 2pc design really hard to get to I was able to remove it to get access to the wires.

Appreciate all the feedback.

 

wow, I can only imagine how many four letter words this took.