Check all the ground wires. Including ground straps to the engine.
Make sure there's no corrosion on the battery cables. It's not uncommon for corrosion to creep up and under the insulation.

Did you get the check engine light read? What was the code?

With the problems being intermittent, it sounds like something is loose or shorted.

 

Where would the ground wires and engine grounds be located?

I looked at the battery cables and I don't think I saw any corrosion, but I will check again.

I had the error code read. It was P1540, vehicle speed sensor malfunction.
Possible causes:
Faulty vehicle speed sensor
Vehicle speed sensor harness is open or shorted
Vehicle speed sensor circuit poor electrical connection

I think the above is just another symptom of whatever caused the other electrical problems. My car is running normally at the moment and no issues have occurred since the check engine light came on, but the problem goes unresolved. :|

 

4 or 6 cylinder?

many folks have had issues with rebuilt alternators for the 3.0 engine - if you have one.

 

4-cylinder

 

The symptom list is a perfect match for very low voltage in the electrical system.

My '98 did that once, it was the alternator.

Your battery may well be good, but charge it soon one way or another.

 

If you were looking for a alternator that is new / unused and not a rebuilt one which may have some undelrying problem that was not addressed.

I have one of these in my 2.5 car, and still have the OEM Mitsubishi USA one waiting to go to the recycler. (It would only charge like 2 minutes in 20 minutes of parked idling when I was testing it with a regular meter at the battery).



I had one of these in 2 days, no deposit. Mine took the $88 Mitusbishi type although my car is a 2002 automatic,

I think the other one is the Hitachi type for $120. I am not sure how subaru assigned each one to each car (some lists appear wrong).
but the part number should be on it. to match with the "parts replacement list" on each alternator.

https://www.dbelectrical.com/alternators/automotive/subaru/outback/2-5-liter/

 

brake light may very well be a separate issue - it will illuminate if brake fluid is low.

That system, if 'in sync' will also alert you to worn brake pads but, on a used car, a full brake fluid reservoir immediately after all 4 new brake pads are installed would be rare. Still, DO NOT allow a brake reservoir to go empty.

worth checking anyway.

 

Just before I got home the low battery light and brake light (as if the handbrake was engaged) turned on.

This combination could occur by coincidence (a failure in the brake and battery charging systems at the same time), but it's more often an indicator that the alternator has stopped working. The Battery and Brake warning lights are linked so that if the Battery light is turned on because the alternator has failed, that will also turn on the Brake light. However, when the brake light is on because there's a problem in the brake system, it will not turn on the Battery Light.

Some of the other symptoms that were reported, such as the gauges malfunctioning, can also be the result of low system voltage, as has already been mentioned.

Parts stores and on-line sites sell small battery voltage indicators that plug into the accessory power outlet. Some are just a few LEDs that light up in different colors depending on the system voltage; others have a digital readout. This can help with an intermittent system voltage problem. Normally the system voltage, with the engine running above idle and little load, will be around 14 V but could drop to as low as around 12.6 V or so. (The H6 alternator output is varied by the ECM depending on engine load.) But if when the gauges etc., stop working properly, and perhaps the battery and brake warning lights come on, the measured voltage is notably below 12.5 (and possibly dropping steadily), that's pretty good evidence the alternator has stopped working.

 

(The H6 alternator output is varied by the ECM depending on engine load.)

By H6 do you mean the engine type? As in the 6-cylinder outback? My Outback is a 4-cylinder automatic. I probably should've written that in the original post.

 

No. If I understand the symptoms, they appeared when driving, not stopped with the engine idling. My thought is that the alternator is failing, causing system voltage to drop to whatever the battery can sustain, but without the alternator the battery voltage will continue to drop. When the engine is running at 1000 rpm or above, the alternator should be putting out ~14 V, so if the symptoms suddenly appear, and the voltage is down below 12.5 or so, the alternator isn't working. (The idea is to "catch it in the act".) And, if some time later the symptoms are no longer there, and the voltage is where it should be, the link is fairly clear.

Now, the alternator can stop working because of an internal problem (which could be intermittent, and therefore not necessarily show up when the alternator itself is being tested), or because of a faulty connection in the wiring to it (some of which has already been mentioned).

Incidentally, this doesn't discount the importance of good grounds, as others have mentioned. If you have a digital multimeter, there's a way to use it (measuring low voltages) to check the grounds.

 

Your hypothesis does seem reasonable. When the gauges start to fail and then flatline at the same time the radio powers off it would seem as the system is low on power then there is no power, but the battery isn't dead yet.

 

Well the battery is dead now and the car doesn't start. Any recommendations on alternators? Everything I've read online says that O'reilly's/Autozone alternators are garbage but I cannot afford a brand new OEM from the nearby Subaru dealership.

 

LKQ or car-part.com

assuming most wrecks happen when a car is operating normally, you might find a good used OEM alternator - with maybe half the miles of your present one.

or, find a local rebuilder, perhaps recommended by a good mechanic, and have them rebuild your alt.

Better than the cheap rebuilts from a parts store.

 

Sadly I do not have the time to scrounge around for a used alternator (thanks college) I could get a refund when this POS from O'Reilly's goes out though, so perhaps I can find something before that happens.

 

I have a 2001 Subaru Outback VDC H6 model and have twice seen electrical symptoms which resolved after cleaning corrosion from ground wires:

1) Gauges wildly fluctuating. Especially notable are unexplained tachometer shifts and impossible readings. On one occasion, shutting either front door hard would trigger the fluctuation. That is what made me suspect some loose connection.

2) Using a voltage monitoring device plugged into the cigarette lighter, observed transient episodes of Voltage fluctuating wildly, from 12.5-14.5 V at idle, suddenly dropping to 8-9 V (even momentarily reading Zero, with the gauges moving wildly, and the engine nearly stalling). Runs battery down after multiple episodes, but jump-starts with normal Voltages immediately.

In each case, clearing corrosion and rust from the ground wires going from the engine to the frame stopped the symptoms. I located them at the top-center of the rear of the engine compartment - two separate wires each bolted to a single piece of metal firmly attached to the frame and connecting to the engine or nearby. Most of the corrosion seems to be at the frame-side but have cleaned the other side of the ground wires also.

We live close to the ocean, and park the car at the beach often, leaving it 4-6 hours while we are out in our boat.
Twice since moving to the coast 5 years ago, have had to clean the grounds. Previously, was inland (Atlanta, GA area) and never saw such issues, did not ever clean the ground wires.

Alternator was replaced preemptively one year ago, when the engine was rebuilt by Dealer for blown head gasket - overheating. That was the only major issue I have had with this car, but a big one. Even though the Dealer obviously re-connected the ground wires at that time, seems that they did not apply any conductive gel, and I neglected to check them until two weeks ago when the issues appeared again. Ground wires were rusty and grimy, cleaned them and no more problems. I clean the exposed end of the wire, the bolt, the lock washer and the metal surrounding the bolt threads with steel wool, then apply a conductive gel. I have also removed some paint to make a better connection around where the wires attach.