Strange charging system issue

[dnp]

I went through a multitude of previous threads, using search, but none are exactly what I'm experiencing.

My new-to-me 99 LC turned on the battery light this afternoon. Immediately thereafter, I took it to an auto parts store and had it checked. First, we took off the battery cables and checked the battery directly. The battery (a few months old Toyota battery) tested good. Then, we reinstalled the cables and checked the alternator. It, too, tested good at 14.3 volts. However, my battery discharge light is still on. Anyone have an idea on what's going on? Thanks

 

[marshotel]

Is it running and starting okay?
If so, I would drive it for a few hours and see if the light goes off.

Does the computer throw a code related to the battery light?
Ask the auto parts store to use their code reader to see if anything comes up.

 

[dnp]

Is it running and starting okay?
If so, I would drive it for a few hours and see if the light goes off.

Does the computer throw a code related to the battery light?
Ask the auto parts store to use their code reader to see if anything comes up.

Yep, it's running and starting fine, and both the battery and alternator check to be good. The computer has not thrown a code (no check engine light). One thing I will note: I changed the oil yesterday, and the PO had apparently put the oil filter on with a 3/4 inch drive wrench with a cheater bar. Since I was at home and without a filter wrench, I was forced to get at the filter from the top of the engine compartment. I got to the filter in the space between the radiator, battery, and the engine, and I was wondering if I might have "disturbed" some wiring in so doing. However, if that were the case, I wouldn't think I would get a proper alternator operation signal at the battery.

Is it possible that the battery light is somehow separate from the alternator charging function? Anyone know what exactly triggers the battery light on the dash and where that "sensor" is located?

 

[spressomon]

FWIW AFAIK my alternator has never put out 14.3V...is it possible the light is coming on from too high voltage?

 

[bigredmachine]

most likely it is the alt on the way out. i seen the same thing at work on a celica where the alt tested good, battry was good, but it was the internals for the alt that were starting to go. new alt and problem solved. i see in your sig line you have 2 100's, try swaping alts and see if the problem follows the alt in question.

 

[TheFuzz]

most likely it is the alt on the way out. i seen the same thing at work on a celica where the alt tested good, battry was good, but it was the internals for the alt that were starting to go. new alt and problem solved. i see in your sig line you have 2 100's, try swaping alts and see if the problem follows the alt in question.

That would be my thought, too.

I agree with the swap idea. Start there and see if you can isolate the problem.

 

[100 TD]

The alternator needs a "sense" supply from the fuse box, if it is missing it will charge higher and turn the light on. Check your ALT-S fuse and wiring to the alt from the fuse box.

 

[uHu]

14.3 V is not high.
In addition to previous post:
Check Alternator-connector
Check engine grounding

 

[mobi-arc]

Take it to a competent alternator/starter rebuilder in your town. They should be able to disconnect the harness from the back of the alternator and ground one terminal on the harness to turn off the alternator warning light. The internal voltage regulator works in conjunction with the alternator warning light and it may be that the alternator is fine and it's a faulty transistor within the voltage regulator that's not turning off the warning lamp. If that's the case, you can simply change the regulator module to solve the issue. Again, a good autoelectric shop should be able to sort this out.

 

[agaisin]

Would 15.44V high (car wasn't warmed up yet)? I see the parts for the alternator on parts diagrams but it's not clear to me what part I would need to replace it. Anyone know where I can get a replacement regulator (if that's what I need)?

 

[mobi-arc]

Measured at the battery, yes , it's a little high. It should be regulating between 13.5 and 14.9. If you rev the engine and voltage stays in the 15's, then it's likely a sensing issue and it's regulating, but slightly high probably due to resistance or poor grounding and may not necessarily be a bad regulator. Regarding where to buy, contact Welcome to WAIglobal Serving the Parts Needs of the Automotive, Heavy Duty, Power Sports Aftermarket - WAIglobal is the preferred parts manufacturer and supplier of alternators, starters, electronics and components for the automotive, heavy duty, ind find a distributor in your area.

Would 15.44V high (car wasn't warmed up yet)? I see the parts for the alternator on parts diagrams but it's not clear to me what part I would need to replace it. Anyone know where I can get a replacement regulator (if that's what I need)?

 

[agaisin]

Disregard my post - I'll spare you the details (https://forum.ih8mud.com/100-series-cruisers/561796-generator-alternator-issues.html#post7392538) but a bad multimeter = bad readings

My multimeter had low battery, blown fuse, possibly toasted electronics and rather than showing ERR on the display (or some visual indicator it was not to be trusted), it showed me inaccruate readings (higher voltage than it should, and lower A than it should). Will need to retest after I get a new multimeter and will post to my thread so as not to hijack this one.