(p0625) generator field terminal circuit low

the_twig_187 · June 19, 2015

Had a 2015 F-550 with 2,000km on it. battery light on with code (p0625) conducted ppt "D" for the code and had 2v on the power feed wire from the high current battery fuse box to the alternator connector (should have been battery voltage 12.6v) I was going to overlay the entire wire but I thought I will give the harness a look over to see if I see the infamous "green fuzz". right where the wire comes out of the main loom (under the air filter box) I saw the fuzz! I peeled back the loom and found the break in the wire. spliced in a patch and vehicle is back to normal.

just thought I would put it out there as this seems to be a bad pinch spot on the harness as there is a hold down bracket holding right at the spot that the wire was broken.

YukonTyler · June 20, 2015

I have done quite a few like that, but never on a unit so new. I'm always thankful that the break is usually right down past the fused link (sense line) and is accessible from the top - otherwise that harness runs in that plastic protective casing and it is not so fun to take that all apart.

Alex Bruene · June 21, 2015

Done dozens. I've seen them break in a few different spots. I usually just roll under the truck and pull on the wires where they come out of the plastic casing. Usually, you'll end up easily finding where the wire is broken, as it will just pull apart.

Matt Saunoras · June 23, 2015

Got one now. High resistance in the voltage sense wire causing it to intermittently overcharge. This one took a little head scratching because the customer insisted it only did it with a trailer hooked up.

I can't find the exact break though but it's in the same spot so I'm just going to have to overlay about 2 ft of wire for now.

Anyone actually ever change that battery cable harness? It's not fun.

Here was how I actually verified the concern. For some reason the extra electrical load was enough to make it act up.

Keith Browning · June 23, 2015

I gave up screwing around with this circuit long ago. Only once was I able to find the open or any damage but armed with this information I will scrutinize this area of the harness a little better in the future.

But, after an honest inspection of as much of the harness as can be made, I access the harness at the upper generator by removing the Cold CAC tube. Open the harness at connector C1104A and cut the AS circuit 2" from the connector. Splice in a 4" length of 20 GA fusible link. Install the appropriate sized eyelet (that ill fit onto the B+ terminal on the generator) to the other end and seal the connections with heat shrink tubing. Re-tape the harness, reconnect the generator and the CAC tube. Clear the DTC and verify the charging system operation.

You can get a bulk roll of 20 GA fusible link from most parts stores. I *think* the eyelet was 1/4"

mchan68 · June 23, 2015

I've changed one of those harnesses before Matt. This was on a one year old salter truck that everything was so badly corroded, the main B+ feed to the starter broke off. Both inner fenders, and even the steering box had to be removed if I recall correctly, just to properly route that harness.

Matt Saunoras · June 23, 2015

The biggest problem I had changing that harness was accessing the 2 grounds bolted to each side of the block. The left size was tough with the lower rad hose in the way. Mine was a salt truck too, damn near burned up when the positive battery cable rubbed through on the front crossmember.

Keith the first 2 repairs I made on that sense wire I did similar to you. I ran a new circuit right over to the left battery though. All the ones since then I've been able to find the break pretty easy.

Alex Bruene · June 24, 2015

I've taken power from the large power terminal at the alternator a few times... I just didn't want to admit it... :hitfan:

batmantech · August 20, 2015

P0620 and P0625 this one had yellow cdc09 wire broken. That goes from generator to pcm.

Of course the wire was open inside the plastic tube channel that goes down under from rh lower engine up and back up the lh side.

lmorris · August 21, 2015

P0620 and P0625 this one had yellow cdc09 wire broken. That goes from generator to pcm.

Of course the wire was open inside the plastic tube channel that goes down under from rh lower engine up and back up the lh side.

Had a couple of those too. First one I found the break and fixed it, second one I didn't bother looking and just over-layed both wires from the alternator.

8WA Sman · July 31, 2016

Had an '09 E-Series that had a P0625(Generator Field Terminal Circuit Stuck Low) - If the GENMON circuit is shorted to ground or the A sense is open, the PCM will set this DTC. This DTC can also be set by a faulty PCM or generator.)

I went through the PPT twice & was going to order a PCM until a contact that I know in Huntsville,AL saved my bacon. Let's look @ the data that we used

So I now know something is not right with this capture, now I have to find out what that is. I de-pin the Genmon(GENLI/CDC15) circuit from the PCM and add my own terminal/circuit & my problem goes away. With more testing I discover that this circuit is being pulled low by CDC25(starter relay to starter solenoid circuit) So how could I have used the IDS to make my life easier??

Let's look

If the circuit is open the Pids should look like this

And a capture of normal operation

I think this is the PCM checking the Gencom

Here is a pic of the damaged wires(LF radiator support area close the BJB)BN-GN/CCD25 & VT/CDC15 were causing the code the other wires also got repaired.