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Old 09-12-2020, 01:37 PM   #1
li.wrx
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Default Alternator Won’t Charge

Hello, hope you all are having a great day.

I’ve been trying to solve this issue for quite a while. I own a 2002 WRX 2.0T.

Essentially I was driving my car and all the electronics slowly dimmed, gauges too, then they turned off completely, the car started to bog out and died. I got it towed home... I replaced the battery, it ran for about 30 minute before it died. I then replaced the alternator (brand new from autozone) as I thought that could be the issue. It still gave me the same problem of dying out after driving on a freshly charged battery. I took my car to a subaru dealership. I paid them to diagnose, they told me it was the alternator. Apparently all connections were checked and fuses, etc. I went to take the alternator into autozone to get it replaced on warranty, they tested it and said it passed with flying colors so I can’t get it replaced.

I just have no clue what to do anymore, if anyone could help me, that would fix this big problem I have right now. Thank you!
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Old 09-12-2020, 02:29 PM   #2
Cougar4
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Check to see if the battery warning light turns on with the ignition switch ON and the engine not started. If that light doesn't work then you need to find out why. The wire color at the alternator may be blk/wht that ties to the light. You should be able to remove the connection to the alternator and with the ignition switch ON, ground that wire connection and make the warning light turn on. If that doesn't happen then you need to check the connection to the light at the dash. You should have voltage on that wire while the wire is not connected to the alternator (open connection) and the ignition is ON. When things are working normally the ignition provides power to the exciter inside the alternator through the warning light. The light is in series with the alternator exciter. That connection also provides testing for the other warning lights. When the alternator is working it builds up a back voltage on that wire and the current to ground stops, turning off the light until something happens to cause a problem within the alternator.

Last edited by Cougar4; 09-12-2020 at 02:35 PM.
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Old 09-12-2020, 02:41 PM   #3
li.wrx
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@Cougar4
Ok so if I fix the connection to the dash light ( which is currently not on ) then the voltage and alternator should charge properly?
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Old 09-12-2020, 02:48 PM   #4
Cougar4
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Yes sir, I guarantee it, or your money back. (Provided that is the only wiring problem to the alternator)
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Old 10-04-2020, 05:21 PM   #5
JakeHarvey97
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Not sure if you got this sorted, but when my alternator died, I measured voltage with the car on and found it at ~11.5v so alternator not charging,
I replaced the alternator, and measured again, this time it had ~14v so charging fine, but I still had cel for alternator fault,

Turns out the ECU wasn't recognising the smart charge function of the alternator, the car can stop/ reduce the alternator charging when it doesn't need full charge, it's controlled using the small extra plug on the alternator, on my car was the blue wire, might just be worth checking connections aren't damaged there?
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Old 11-05-2020, 10:26 AM   #6
DrazaTech
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Quote:
Originally Posted by JakeHarvey97 View Post
Not sure if you got this sorted, but when my alternator died, I measured voltage with the car on and found it at ~11.5v so alternator not charging,
I replaced the alternator, and measured again, this time it had ~14v so charging fine, but I still had cel for alternator fault,

Turns out the ECU wasn't recognising the smart charge function of the alternator, the car can stop/ reduce the alternator charging when it doesn't need full charge, it's controlled using the small extra plug on the alternator, on my car was the blue wire, might just be worth checking connections aren't damaged there?
This smart charge function, is it something that is in the alternator?

I am having issues with my girlfriends Subaru and this whole thread is basically the issue. I took out the gauge cluster to test out the light finding out it it’s solder in. So, I guess I have to check the wire connections to the alternator.


My question is this, is this something that comes with an OEM alternator? Not “any” alternator?

I ask because the original alternator died and the father had it taken to this place that specializes in repairing alternators for the cheap. Long story short, they gave us another alternator and told us the old one was fried from a bad connection in the car and blamed it on the battery. Things were fine till the car started randomly dying from charge. I did the voltage test, and definitely not meeting the 14v quota and hovering at 11.8v.

So check the wires from the alternator? I basically gotta reattach the gauge cluster lol.

Bulb looks fine, tried to do it with the multimeter but as a poster (sorry can’t give credit typing this on the phone) mention earlier in this thread supplies power to the other warning indicator lights it’s probably why the multimeter test failed on me.
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Old 11-05-2020, 11:04 AM   #7
Cougar4
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There is an added circuit in some of the newer alternators that use the ECU to control the alternator output. Instead of two wires going to the connector on the alternator there are three wires.

The battery warning light in the dash passes current on to the exciter inside the alternator. If the exciter has no power supplied to it then there is no output to the battery. To test the operation of the warning light you should be able to turn the light ON by grounding the lead going to the alternator. The lead color is usually blk/wht.
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Old 11-11-2020, 07:05 PM   #8
ASubieNamedRuby
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Quote:
Originally Posted by Cougar4 View Post
Check to see if the battery warning light turns on with the ignition switch ON and the engine not started. If that light doesn't work then you need to find out why. The wire color at the alternator may be blk/wht that ties to the light. You should be able to remove the connection to the alternator and with the ignition switch ON, ground that wire connection and make the warning light turn on. If that doesn't happen then you need to check the connection to the light at the dash. You should have voltage on that wire while the wire is not connected to the alternator (open connection) and the ignition is ON. When things are working normally the ignition provides power to the exciter inside the alternator through the warning light. The light is in series with the alternator exciter. That connection also provides testing for the other warning lights. When the alternator is working it builds up a back voltage on that wire and the current to ground stops, turning off the light until something happens to cause a problem within the alternator.
I think I'm having the same issue. Makes me sad. I just want to drive
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Old 12-04-2020, 11:06 PM   #9
DrazaTech
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Quote:
Originally Posted by Cougar4 View Post
There is an added circuit in some of the newer alternators that use the ECU to control the alternator output. Instead of two wires going to the connector on the alternator there are three wires.

The battery warning light in the dash passes current on to the exciter inside the alternator. If the exciter has no power supplied to it then there is no output to the battery. To test the operation of the warning light you should be able to turn the light ON by grounding the lead going to the alternator. The lead color is usually blk/wht.
I tested the operation of the bulb. Unfortunately, for this Subaru, it didn’t follow the bulk/wht lead since it has a red / green / blue color layout for the wires. I believe it was the red one that triggered the bulb to turn on when I grounded it, so I know the bulb is working.

I checked the fuse and also the wires and they all seem fine. Based on the test you recommended, it points to the alternator.

I am trying to convince the old man that is the alternator but he refuses to believe it is.. that there’s some sort of ground and refuses to believe the “charge lamp” would be a thing (if it was blown) that would hinder the car from charging.

And that he’s worked on many cars and never heard of this “charging cut off function” govern by the ECU. I own a Toyota MR2 91’ so this thing is also new to me but I am not shocked by things like this since I know each manufacturer always wants to throw their own bells and whistles to “innovation” per generation of each vehicle.

Anyway you could break it down even further Cougar in layman’s terms, where I could make my argument more convincing? Lol sorry this may be a bit more than the usual help. Greatly appreciated, I looked at your post history and you seem pretty knowledgeable, dunno from experience or education but your methods make sense in my head. Perhaps it’s my IT background but troubleshooting seems spot on. ***129311;***127995;
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Old 12-05-2020, 11:59 AM   #10
Cougar4
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I assume the alternator you are working on has three wires going to the back side of the alternator. One lead is the battery sense or '+S' lead. That lead is connected to the battery and lets the alternator know what the condition of the charge is on the battery. The wire going to the warning light and battery is called the 'Lamp' lead or 'L' lead. It also provides power to the exciter inside the alternator. On two wire alternators that is all you need for the alternator to operate. The three wire design incorporates a lead from the ECU to control the alternator output. It is supposed to provide more efficient alternator/engine operation if I understand it correctly. When charging current isn't needed the alternator is disabled, which puts less load on the engine.

I think all three wires will have close to battery voltage on them when the alternator is working correctly but I am not real sure about the ECU lead. I haven't worked on that design. Check the voltages on the wires while the engine is running and let us know what you get.


Quote:
Originally Posted by DrazaTech View Post
I tested the operation of the bulb. Unfortunately, for this Subaru, it didn't follow the bulk/wht lead since it has a red / green / blue color layout for the wires. I believe it was the red one that triggered the bulb to turn on when I grounded it, so I know the bulb is working.

I checked the fuse and also the wires and they all seem fine. Based on the test you recommended, it points to the alternator.

I am trying to convince the old man that is the alternator but he refuses to believe it is.. that there's some sort of ground and refuses to believe the "charge lamp" would be a thing (if it was blown) that would hinder the car from charging.

And that he's worked on many cars and never heard of this "charging cut off function" govern by the ECU. I own a Toyota MR2 91' so this thing is also new to me but I am not shocked by things like this since I know each manufacturer always wants to throw their own bells and whistles to "innovation" per generation of each vehicle.

Anyway you could break it down even further Cougar in layman's terms, where I could make my argument more convincing? Lol sorry this may be a bit more than the usual help. Greatly appreciated, I looked at your post history and you seem pretty knowledgeable, dunno from experience or education but your methods make sense in my head. Perhaps it's my IT background but troubleshooting seems spot on. ***129311;***127995;
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Old 12-19-2020, 07:59 AM   #11
DrazaTech
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I don't know exactly how to check the wires for the voltages when the engine is running. Do I stick the multimeter prongs where?

Second, the alternator was taken back to that alternator shop and her father mention something to do about the regulator and they did something to it. I don't know what, perhaps replace the regulator but once we got the alternator back and we wired it back up to the car the following happened:

- Charging Lamp was on (finally) when key IGN ON
- Charging Lamp / Brake warning lamp remained when car was fully started
- MPH did not read right.
- Car started with charge voltage >~ 15V

We took it for a drive and we noticed the Gauge cluster was acting up on the MPH and the car kept having somewhat of a rough idle and wanted to stall.

I did a bit more research and reading and someone mention the ALT-S fuse might've blown. It did. Replaced it.

Now the following occurred when the car was started fully:

- Charging Lamp turned off but briefly came back when brakes were applied
- Brake warning lamp completely off
- Charging Lamp would intermittently turned on / off
- Multimeter shows car charging between the range of 14.2~14.6 (was happy about this)

But we also noticed this:

- Multimeter charging would jump the threshold from 14.2 to 14.7 to 14.4 to 14.6, 14.3 and so on and so forth but it wouldn't stay steady and you could hear it with the engine idle.

- Car would stall out of again.

We did this various times trying to rack our heads as to why it was doing this... we believe the system is charging but what was throwing us off was the charging lamp light coming on and back off. It would only turn back on right if the car felt like it was about to stall.

- Battery shows a 12.4V with car off.

Any ideas what could be happening now?
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Old 12-19-2020, 10:11 AM   #12
Cougar4
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In order to read the voltages on the wires you would need to use like a needle probe to pierce the wire insulation near the connector. The holes should be then sealed with something like RTV so water can't get inside the wire.

The charging voltage is good so the battery is getting charging current but it seems that there is still something not right within the alternator. I would check the AC ripple voltage while the engine is running around 1,500 RPM. The voltage should not be more .1 volt AC otherwise there are bad diodes in it.
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