2005 ford 500 p0622

Had new alternator installed no power on why/blk wire at alternator connector ran new wire from fuse 18 to alternator now have power. But still throwing the code. I guess next move is scope the control wires. Does anyone have scope captures of the 2 communication lines 

Hi Cheryl, I'm T.J. and I am the foreman at an independent shop that specializes in Ford/Lincoln/Mercury, so have dealt with a handful of these PCM controlled alternators. 9/10 times it needs an alternator, but this one might be that outlier. Just a few questions to help me catch up to where you're at so far. First, is the "new" alternator actually new or is it remanned? I've seen a reman be faulty fresh out of the box on these applications. Then, you said it was missing power on wht/blk wire from fuse 18 so a new wire was ran to power that circuit, has any diag been done on why there is no power from that fuse? While we're on the power feed subject, does the heavy B+ cable have 12 volts on it at the alternator stud KOEO? If yes, is there any voltage drop of that cable, tested from the battery positive post to the B+ stud on the alternator while running? Should have .2 of a volt drop or less. Same goes for the wht/blk wire between the regulator connector and the battery positive post. If those checks are good, then there is a quick and dirty test to see if the alternator can actually charge. Disconnect the connector and run the engine at 3,000 RPM while monitoring voltage at the battery. Should self excite to 13.5 volts, if so, then it is able to charge and the PCM control will have to be scoped. I have scope captures of those circuits, failed and working, but am unable to upload them here, sorry to say. The GEN MON and GEN COM circuits should show similar duty cycle square waves on the scope, and should increase in duty cycle as loads are increased. If you find a fault in either of those circuits, inspect for harness contacting the A/C lines on the rear of the passenger side of the engine bay, and also near the rear cylinder head lift hook. Ford has acknowledged there may be chafing in those areas, affecting the PCM circuits to/from the alternator. Very long winded, I know, but hopefully you find some of my advice useful! Good luck, and hope to hear back from you.
Travis T.J. Harrison

Cheryl, I've got some known good captures in this thread:

www.scannerdanner.com/forum/diagnostic-t...ernator-testing.html

The quick and dirty way to verify the GENCOM and GENMON circuits is to disconnect the alternator and short the two together. Get your scan tool of choice set up to watch the GENMON and GENFDC PIDs and start it. They should directly mirror each other. Check out the thread above for more details.

I have power on the large battery stud. .220 mv drop. Same for the wh/blk wire. Unplugged alternator revved it up to 3000 rpm went to 13.5. I’ll try what Tyler suggested 

Awesome, let us know how it goes.

Tj do you know what the gen mom and gen com voltages should be connector unplugged at alternator? I have no signal on gen mon. Or gen com does the pcm send out a bias voltage for alternator to pull down on the com wire??

GENMON has a 10ish volt bias coming from the PCM, which the alternator pulls to ground.

There is no real bias on GENCOM that I remember.  

So check for 10ish volts coming from pcm at connector? I’ll cut wire to eliminate a short to ground see what happens

Well think I’m figuring something out. The battery sense wire and gen com wire are switched in the pigtail someone put on. So swapped them and no more battery light p0622 doesn’t come back.

Generator field circuit problem.
Does the charging system work ok? Your battery and battery connections ok?

wrote:

Well think I’m figuring something out. The battery sense wire and gen com wire are switched in the pigtail someone put on. So swapped them and no more battery light p0622 doesn’t come back.

Nice find! So fixed?

It’s been gone for a week so I’m going to assume it’s fixed