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Old 02-04-2012, 10:48 AM   #1
Jays04WRX
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Default Battery, Brake, and Rear Diff Temp light flickering intermittently

Hi Folks,

I've been having an intermittent issue with my 2005 STi lately. For some time, the rear differential temperature light has been flickering while driving. It usually turns off while at a stop, and begins again while rolling. The nature of the flickering changes day to day. I had figured that this was a bad ground, and haven't been able to look for the rear diff ground strap yet.

Recently, while driving down the road after having to jump start my battery (car sat for several weeks in the cold), my voltage dropped severely to the point where the battery, brake, and ABS lights came on. I pulled the car into a parking lot as the gauge cluster died, and killed the ignition. The car still had the stock battery, so I brought it to Napa where it tested bad, and I replaced it.

A week or so after that, while letting the car warm up I noticed the battery light came on. I checked voltage across the battery and found that the alternator was not charging. I parked the car and went to start it several days later, and the battery was charging appropriately. I assume I probably have an issue with the alternator, but is there a way to check for sure if its failure is intermittent?

When driving the car the other day, I noticed that the battery, brake, and rear differential temp lights were all flickering in unison as I idled at a stop. I shut the car off, ran my errand, and when I came back and started it again, the problem was gone.

I feel like I have a somewhat complex set of issues. Where should I start troubleshooting?

Thanks!
Jay
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Old 02-04-2012, 10:56 AM   #2
Cougar4
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It sounds like some of the diodes in the alternator are bad. Check for AC voltage ripple on the alternator output while the engine is running around 1500 RPM. If you have over .1 volt AC volts then the alternator is defective.
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Old 02-04-2012, 10:58 AM   #3
Jays04WRX
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Is this test valid even when the lights aren't flashing? Can diodes fail intermittently, or should checking this once be the definitive test? It certainly makes sense that the alternator could be bad, seeing as how it was failing to charge the battery at one point.
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Old 02-04-2012, 11:38 AM   #4
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You can check the voltage at anytime. Diodes do fail fairly often since there is a lot of heat generated due to the high current load.
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Old 02-04-2012, 12:08 PM   #5
Jays04WRX
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Just went out and fired up the car. Battery is charging normally (14.7 VDC across the battery) and my cheap radioshack multimeter reads 0 VAC across the battery. Of course, the lights are not flickering at this point. Is it plausible that the diodes are failing intermittently? I will definitely check for AC voltage across the battery next time they flicker at idle.

What are these diodes, and what do they do?
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Old 02-04-2012, 01:19 PM   #6
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The diodes convert the alternating current (hence why it's called an "alternator") into direct current that the car can use. There's a bunch of them and it's very possible to have one or more fail without being obvious. When this happens the effective output of the alternator is reduced, and with enough AC component in the output you'll start to get those odd symptoms like flicker, warning lights, and so on. A simple meter test on the battery may not always show the problem, but a scope will or you can remove the alternator from the car and take it to a parts store or rebuilder to be tested.
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Old 02-04-2012, 02:22 PM   #7
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Since you are having an intermittant problem then having some bad diodes is most likely not the case here. Once a diode goes bad then that is it. It won't fix itself and the problem will remain. I suggest you clean the battery connections using a battery post cleaning brush. There may be a thin layer of corrosion on the connection surfaces causing the trouble. Also make sure that the connections at the rear of the alternator are making good connection along with output lead of the alternator. Be careful with the output connection as it is always hot to the battery.
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Old 02-04-2012, 06:29 PM   #8
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Check your serpentine belt. i had this issue and my serpentine belt was a little loose. tighted it up and it was good to go.
Hope this helps,
Joel
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Old 02-08-2012, 09:06 PM   #9
Jays04WRX
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Thanks for the suggestions folks. My best guess at this point is that the voltage regulator in the alternator is going bad. When the car is cold, the car behaves fine. After about 20 minutes of driving, the alternator ceases to charge and the brake and battery lights start to flicker, then become solid as the voltage across the battery drops far enough. I have ordered a new Bosch alternator from RockAuto, so we'll see if this solves my issue.

My battery terminals are clean, and the connections at the alternator look fine as well.

I will report back when I get the new alternator and let you all know what works out.
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Old 02-08-2012, 10:13 PM   #10
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A replacement alternator will most likely solve the trouble.
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Old 08-07-2017, 11:47 AM   #11
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Resurrecting this, as I'm having the same exact problem. The r.diff, battery, and Brake lights will come on in unison, and flicker on and off in unison. Seems like just a connection and/or ground somewhere is loose. Did replacing the alternator fix the problem?
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Old 08-07-2017, 01:37 PM   #12
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Quote:
Originally Posted by mav1c View Post
Resurrecting this, as I'm having the same exact problem. The r.diff, battery, and Brake lights will come on in unison, and flicker on and off in unison. Seems like just a connection and/or ground somewhere is loose. Did replacing the alternator fix the problem?

Its been awhile since I had a similar (may have been same) situation. I had advance zone confirm that my alternator was shot. I replaced it with one of these ordered directly from LSA. I have no affiliation with LSA. Hope this helps.

http://lancasterstarterandalternator...ternators.html
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Old 08-07-2017, 05:35 PM   #13
STeeIguy
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Did Anyone Have Issues With Their Ac Compressor Clutch? I Replaced My Alternator And Same Things Were Happening. I'm Going To Be Replacing The Whole Ac System This Weekend.
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Old 08-08-2017, 01:40 AM   #14
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Quote:
Originally Posted by mav1c View Post
Resurrecting this, as I'm having the same exact problem. The r.diff, battery, and Brake lights will come on in unison, and flicker on and off in unison. Seems like just a connection and/or ground somewhere is loose. Did replacing the alternator fix the problem?
it did for me.. i had the brake and battery lights on just last month; the alternator was ultimately failing

glad i had an extra in my garage to replace it
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Old 08-08-2017, 03:26 PM   #15
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Quote:
Originally Posted by STeeIguy View Post
Did Anyone Have Issues With Their Ac Compressor Clutch? I Replaced My Alternator And Same Things Were Happening. I'm Going To Be Replacing The Whole Ac System This Weekend.
If you are replacing the AC due to your warning lights flickering then I suggest you hold off doing that. If you suspect something is wrong with the AC clutch then disconnect the connector to it and then see what happens after you isolate that. The only time the warning lights flicker is when there are bad diodes inside the alternator.
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Old 08-08-2017, 03:56 PM   #16
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If Cougar4 states something electrical, I won't argue unless I do more testing, he keeps me honest and helps a lot of others.
Just saying......
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Old 08-08-2017, 04:34 PM   #17
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The Cat isn't always correct and can get off the trail at times. You help keep me honest too Charlie-III. Just saying....
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Old 08-31-2018, 02:26 PM   #18
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Jay, did you decide if it was the alternator or not?
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Old 08-31-2018, 02:47 PM   #19
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Last login 6-9-15, he ain't gonna answer.
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