'I' circuit (904) generator fault on 2001 Ford Powerstroke

The ‘Charging System Warning Indicator’ has come on in my 2001 Ford Powerstroke, with the single generator option. I replaced the generator since I initially thought it was bad, and the old one had close to 100,000 miles on it and had some problems with the windings. That did not solve my problem, however. I have the FCS2000 Workshop manual and have gone through the first several checks. Both fuses in the PDB are good. There is battery voltage at the B+ terminal of the generator. There is battery voltage at the ‘A’ terminal (O/LB - circuit 35) of the disconnected 2-wire connector going to the back of the generator. The first failure is at the next test, which asks to test the voltage on the ‘I’ circuit (LG/R - circuit 904) with the connector re-attached and the engine running. It’s looking for more than 1 volt, I see 0.070 volts. (Interestingly, a table at the start of the diagnostic section says that the I circuit should show 12-15V with the engine running, and 1-3V with the key on/engine off. ??? ) Anyway, my questions: 1) Does this indicate a fault between the generator and the instrument cluster? 2) Is the voltage on this circuit driven by the instrument cluster or the generator? 3) If driven by the cluster, can I snip the wire and attach the connector side of circuit 904 to a switched and fused +12V source to enable the generator to charge?

Are you not following the wiring diagram? Does the wiring diagram show the wire going to the engine computer, or what?

The wiring diagram shows circuit 904 going between the I terminal of the generator and the instrument cluster.

The wire provides voltage to the exciter of the alternator. The warning lamp in the cluster is in series with the connection to power at fuse #29. Since you say the warning lamp works it sounds like fuse 29 is ok. If the warning lamp turns off when you remove the connector at the back of the alternator (key ON, engine NOT running) then I would say you have a bad alternator out of the box. Verify you have battery voltage on all the other leads, if you do then I think you need to return the alternator.

With the connector disconnected, key on, engine not running, the voltage at the wire side of the connector (not the generator side) is 0.022 V. B+ terminal on generator has +12 V, A terminal on the wire side of the connector has +12 V.

Since you have no voltage on that lead check to see that voltage is getting to both sides of fuse #29. If you have voltage there then it appears that there is a break in the lead somewhere between the fuse and the connection to the alternator.

You stated that the alternator warning light was on. I assume that when the wire is not connected to the alternator and the ignition is ON that the warning light is OFF and if you connect it up the light is ON. Is that correct?

Voltage needs to be present on that lead to start up the field action. Check the resistance on that lead to ground with the connector removed and ignition OFF. See if there is a short to ground on the lead.

With the key on, there is +12 V (minus a little) on fuse #29. Does that fuse connect directly to circuit 904?

When the wire is not connected, and the ignition is on, the light still stays on.

Resistance to ground with the connector unplugged is 2.6 ohms (which would explain why the light is always on above).

I have a wiring diagram off the web (FWIW) that shows that this circuit comes from the instrument cluster. So am I to assume that the either the wire or the connection within the cluster has a low resistance path to ground? Is there any chance of finding that wire under the dash?

The fuse does power that circuit.

It does appear you have a short to ground on the lead coming from the cluster going to the alternator. I would guess the trouble is under the hood rather than the dash but I could be wrong about that. You should be able to find the same wire color running to the cluster.

I will try to trace it out. If it’s in the wire, I’d like to fix it. If it’s in the cluster, I’m not sure that I would spend the money to have it diagnosed and fixed.

After talking to the old guy who runs the local alternator reman shop where I got my swap, I went ahead and did an experiment last night where I snipped the ‘I’ circuit wire and attached the generator end to +12V to energize the regulator. This drew about 1 A with the key on/engine off, but only a few 10s of mA when the truck actually was running. At this point, the generator actually did start to charge the batteries.

So, if I cant trace the wire and find the short, I may just hook that ‘I’ circuit lead on the generator to some other switched/fused +12 V circuit. I’d like to hook it to one that’s only energized when the engine is running, as opposed to just when the key is in the on position. Do you know of any such tap point?

Thank you for all the help, by the way - I really appreciate it.

There are only about 10 models/sub-models of Ford trucks which have the Power Stroke engine. If you would specify which one you have, it would help would-be respondents a lot. We, me, or I, would then know which particular wiring diagram pertains to your vehicle.

2001 F350 4x4 Crew Cab, full box, 6-sp manual transmission, manual hubs, trailer tow and camper packages, 373 Limited Slip, single generator, off-road package - delivery 11/2/2000. There’s probably a few more options I can’t remember off the top of my head - I hope this narrows it down enough - let me know if not.

You’re welcome for the help.

I doubt the problem is inside the cluster. I would suspect that the trouble may be where it goes through the firewall or in the engine area. You should be able to find the other end of the wire going into the cluster. Once you find the right color wire ohm it out to prove it is the correct one. If you can’t find the trouble and correct it you can cut the wire at the cluster end and run a new wire between the two ends. You really need to keep the warning light in the circuit so there is a warning when trouble happens.

This simplified wiring diagram for the 7.3L turbo-diesel engine, with “Single generator without dual generator giveaway” may be more help that the factory multi-page, segmented, diagram. http://www.autozone.com/autozone/repairinfo/repairguide/repairGuideContent.jsp?chapterTitle=Charging+System++2001&partName=Wiring+Diagrams&pageId=0900c152801dfa45&partId=0900c152801df4c0

Well - I bit the bullet and dug around under the dash. There was a big gob of wires that came through the firewall, to the right of what I assume is the PCM, which is mounted on the left wall of the driver’s footwell. The bunch of them lay in a little tray with that had a jog to one side. With some difficulty, I removed the tray to get at all the wires.

As I feared, there were 3+ light-green w/red wires in that bunch of 50+ wires. I was just hoping that Ford kept the same wire color scheme as the circuit progressed, so it would be one of these 3.

As I said before, I had already cut the LG/R wire at the generator. I then hooked a 12 foot 16 awg jumper wire from the end in the engine compartment that went back to the firewall (not the connector end), and ran the other end of the jumper into the cab for easy access. Now I had an extension of the instrument cluster side of the circuit back in the cab with me.

I then took a needle and poked through the insulation on each LG/R wire and measured the resistance between it and the loose end of the jumper wire I brought back. Two of them gave a negative resistance, meaning that they must have had some voltage on them and were driving current through the meter’s positive (probing) lead. The 3rd one gave 0.6 ohms, which was just a little more than what I read across just the jumper wire itself, so that looked like the right one. As a check, I put a 1.236k ohm resistor between the same end of the LG/R wire in the engine compartment and the start of the 12 foot jumper, then I retook my measurements. Only one wire of the three (the same one) gave the correct resistance value - 1.236k ohm. So, I cut this wire, hoping that the short to ground was somewhere between where I cut and the engine compartment.

Now I turned the ignition on, but didnt’ start the truck - the charge warning light was now off, gloriously, since the circuit was no longer shorted to ground; the short was indeed downstream of my cut. I took a small jumper and re-connected the two ends of the wire I just cut and verified that the charge light came on again. No doubt that this is the circuit and the short was between my cut and the generator.

I went ahead and unhooked the large jumper wire then ran it through the firewall inside a flexible conduit I already had in there for some wires I ran previously for some gauges. Hooked one end up to the generator, the other up to the loose end of the LG/R wire I just cut that went up into the dash toward the IC. I set the DMM for volts and now measured 1.8V to ground with the key on/engine off - just like the book says. I started the truck and after several seconds the generator kicked in and started charging - must be a delay in the generator.

Thanks to all who helped. It took me longer to figure this out than I had hoped, but at least I learned something and saved some money.

Good work. Glad you corrected the trouble and thanks for the feedback.

I learned about the charge warning light a long time ago when trying to fix a charging problem on a Ford truck. I spent a lot of time trying out figure out why a good alternator wouldn’t work. All because I didn’t know about the need for the warning light to work in order to supply current to the exciter. After a lot of hours spent on the trouble I finally cleaned the bulb socket and then the bulb worked and so did the charging action. These kind of lessons stick with you. Now that you have been down that road also I am sure you will be checking that first if you ever see that kind of problem again.