Alternator failed - no warning light?
 

I'm a little baffled; the alternator failed (again; 3rd time; thank you O'Reillys) - but there was no warning light while the car was draining the battery. Shouldn't there be one?

Even after I charged the battery back up and re-installed it to get the car home to pull the alternator - no warning light of any type. I know the car was running on the battery as I verified it with my multimeter.

I would normally never put an auto-store alternator in a vehicle, but when 5.5 years ago it failed, she wanted the car running the next day and didn't want me to get parts and rebuild it myself. That has been a nightmare as they keep failing - first one last 18 months, this one 4 years. So this is the third alternator on the original purchase (free replacements).

My plan now is to go to Romaine Electric and get a good VR and just pull the thing back out next week and toss the "new" VR in this unit and put in a known good (brand) part. But I'm still wondering why no warning...

That does sound odd. Since you're one of the few members that typically provides help, I won't ask if you checked if the warning light illuminates before stating the car!
Did it previously illuminate with earlier failures?
What were the voltage readings and did they vary with engine speed?

I don't recall if it lit up before; I'm not the main driver. All she said happened was that all the dash lights started flickering before it sputtered and stopped. If there'd been a prior illuminated lamp, she'd have said something and not missed it; I know for sure. I took the battery out, charged it, re-installed it and no light (and the alternator was outputting nothing - voltage check showed only battery voltage. New alternator showed 14.65 at idle and everything above (multimeter readings).

I'm wondering why the PCU isn't passing along a warning?

I guess tomorrow one thing I could do is plug in the OBDII reader and then look at what the PCU is saying voltage actually is with my Torque Lite app, and then pull the alternator plug and see if it is at least indeed reading it.

Odd. It did look like the warning lights all illuminated during start-up, so I don't think it's a burned-out bulb; guess I should double check that.

Hello,

I have a theory on what happened there - the thing is that, from my understanding, the light on the dashboard is not triggered by low voltage, but by the lack of charge by the alternator. To my knowledge, there is a controller in the voltage regulator that senses the voltage on one of the phases, and either opens or closes connection of the light to Ground. It is also a "standalone" system, meaning that, at least in my 2000 ES300, there is no direct connection between charging system and ECU.

I think what happened in your situation is that the alternator was charging, though the output was not nearly enough, hence the voltage dipped to the battery level. The same situation was happening in 3rd-gen ES, since their alternators are way too weak from the factory, therefore with headlights and seat heaters on, you would only get around 12.5V (I even managed to get it down to 11.8V once, and no light came on)..

Well, that is how I understand it, so I would appreciate if someone would correct me if I am wrong.

Hope this helps and best of luck!

That helps a lot. I know enough of chemistry, physics, mechanics, electrical theory to get by but I am bad at reading electrical diagrams. What you said makes perfect sense to me when I parse it out. As the VR failed, (I think) in toto instead of just one rectifier or phase, that scenario works. I can see how a total VR failure would thus fail to register a low charging light.

I know you have not not been on this forum along time (a year I guess I see), but I have read and appreciated your very technical responses to others in the past. Thanks for being here! We lost a huge asset when (the now internet/youtube famous) SpeedKar99 left us, glad you can step in with help. Much appreciated!

I think what I'll do is next spring (I have a lot of car projects to address, in fact bought a low-mileage Volvo S60 2.5t awd just tonight for my step son) is go buy a high quality VR and pull this alternator back out, throw away whatever junk board they put in them is, and then feel like I can trust it for 100k+ miles more. I know it's not the stator/coil/pick-up failing repeatedly but the VR board. Now that you explain there's a specific IC on the VR board that communicates, that makes it seem so much clearer.

Thanks!

Glad I was able to help!

What I meant by my previous post is that you alternator may be functioning, it is just way too weak. You have a raw, 3-phase AC voltage leaving the alternator before the rectifier, and one of those phases gets directed to the controller in voltage regulator, letting it know that the alternator is working, and therefore switches the light off. Granted, failed voltage regulator will also prevent the light from functioning, but it is probably not the case in your scenario. What voltage in particular were you getting? The best way to check the alternator is to take it to the car parts store and have them test it, they usually do it for free. Other than that, there are some other, "less than perfect" techniques, which I wouldn't necessarily recommend, like bypassing the regulator and checking the output while in the car.

The problem is that quality OEM regulator costs around the same as the whole alternator, so you best bet will probably be to return your current alternator if you can, and get Denso remanufactured one, which costs around the same, while being that much better. I have one, and they do replace almost everything, including rectifier and voltage regulator, leaving only rotor and stator. I am not sure which car is in question, but I am fairly certain Denso 210-1028 will work for both 3rd and 4th generation.

Hope this helps and best of luck!

If it was making voltage, it was less than battery voltage as I measured it there and it was just battery voltage.

I would think the like would trigger at under a measured voltage, not just present/absent? Or maybe not....

Here is a thread describing the situation when B+ wire that connects battery with the alternator was loose. The voltage on a running car without charge will be around 11V, though that said, it is not what triggered the light in that case, since, to my knowledge, the indication system has no direct way of checking the voltage. I think what happened in that case is the alternator charge depends on the battery voltage (smaller the voltage, more charge alternator produces), and since the voltage wasn't going up, the light came on. In your case, there probably is a voltage on a stator, hence why the light never came on. That said, it is probably not enough for the car, hence why you saw low voltage readings. Well, at least those are my guesses.

Hope this helps and best of luck!