No Charge '04 LX 470

[Dirt J]

You asked for suggestions, so I'll give you mine again, and then shut up so hopefully I don't come across as rude.

Crank the truck and check the voltage across the battery terminals. Should be over 13v if alternator is charging. Directly at the terminal on the alternator is best because that eliminates another point of failure.

If it's not over 13.2, per the FSM, then the alternator is not charging.

So, why is it not charging?

1. Most likely its something internal to the alternator, possibly the regulator which gets its input from the 7.5 amp-protected "sense" wire. Could be some other thing internal to the alternator. (They are rebuildable if you want to dig in but not my cup of tea.) You would not be the first person to get a dud replacement from the parts store. Has happened to me on a different vehicle.
2. Wiring issue: you said you already replaced the positive lead to the battery, though that should not have caused a no-charge situation, be maybe a lower-than needed charge situation. Or a sense wire issue. Again doubtful but you could check for continuity on either side of the fuse and at the plug.
3. Drive belt. I think you'd have other issues (A/C, PS) if the drive belt was not turning the alternator pulley correctly.
4. ...that's all I can think of!

Good luck! I hope this is helpful.

 

[Dysfunctional Vet]

You asked for suggestions, so I'll give you mine again, and then shut up so hopefully I don't come across as rude.

Crank the truck and check the voltage across the battery terminals. Should be over 13v if alternator is charging. Directly at the terminal on the alternator is best because that eliminates another point of failure.

If it's not over 13.2, per the FSM, then the alternator is not charging.

So, why is it not charging?

1. Most likely its something internal to the alternator, possibly the regulator which gets its input from the 7.5 amp-protected "sense" wire. Could be some other thing internal to the alternator. (They are rebuildable if you want to dig in but not my cup of tea.) You would not be the first person to get a dud replacement from the parts store. Has happened to me on a different vehicle.
2. Wiring issue: you said you already replaced the positive lead to the battery, though that should not have caused a no-charge situation, be maybe a lower-than needed charge situation. Or a sense wire issue. Again doubtful but you could check for continuity on either side of the fuse and at the plug.
3. Drive belt. I think you'd have other issues (A/C, PS) if the drive belt was not turning the alternator pulley correctly.
4. ...that's all I can think of!

Good luck! I hope this is helpful.

No umbrage taken sir. I appreciate the info.
I'll use this as a checklist once I can get back to it. Will advise.

Very Respectfully,
Dysfunctional Vet

 

[Dirt J]

@Dysfunctional Vet I just realized that I posted the EWD for the early year model 98-02. I just checked the 04 EWD and it is indeed different.

Thankfully, I think the egg on my face is minimal bc it appears, while the ECM is involved in the later year models, it is only to get input from the alternator for the gauges, etc. The arrow on the black/oranges-stripe wire shows the flow of the current towards the ECM. The sense wire still performs that "exciter" function.

I also checked the 2004 FSM and the charging system check steps were the same as the 2000 FSM is was looking at. So, all that said, my above $0.02 still stands.

 

[Dysfunctional Vet]

So the ECM does not control voltage on an '04, it only identifies/records it?

 

[Dirt J]

Correct. I think the catch is the way the gauges changed between early/late year models. Looks like the early year dash voltage gauge comes straight from the alternator. Late year it is routed through the ECM.