Don't ask why or how, I'm humiliated enough. Reversed polarity, horn blew, quickly disconnected however, now car won't come on at all when key is turned. DEAD AS A DOOR NAIL. I checked fuses. No blows. How do I proceed to troubleshoot?

2011 2.4 outback

 

You likely blew a main fuse or fusible link. You checked fuses in the dash panel or under the hood - or both - and didn't find that the main was blown? You used a meter or a test light to check? You need to look at the fuses under the hood if you didn't.

 

Thank you... I visually checked the micro-fuses in both. I will recheck both. Meter not currently available, I am stranded. Horn, light, and electric seats work. Maybe anti-theft?

 

Not sure if "DEAD AS A DOOR NAIL " refers only to the engine cranking/firing, or everything - does anything else operate now that the battery is correctly connected? Headlights, parking lights, horn?

 

Not sure if "DEAD AS A DOOR NAIL " refers only to the engine cranking/firing, or everything - does anything else operate now that the batter is correctly connected? Headlights, parking lights, horn?

Yes...horn, lights, electric seats. No interior lights or gauges or gauge lights. Just no activity when I turn key forward. Maybe Anti-theft?

 

Probably should have ignored what you said and asked anyway because I took it that you were installing the battery. Now I realized it could be that you were attempting to boost and that's where the reverse comes in. So maybe silly question, but if you don't have a meter, how do you know the battery isn't dead flat because a light was left on overnight?

 

Actually, I was re-installing a new battery when I went braindead. I was hiking and did leave an interior light on. I needed a new battery anyway... so I got ride to town and back with the new battery.

 

Fusible Link? Dicked by fickle finger of fate!

 

Fusible Link?

That's what I have been thinking from the start but unless you know what to look for and don't have a meter, then I cannot think of anything to add. Anything I read about this indicates a blown fusible link (not necessarily the main) under the hood for those models that are wired that way. I would think the horn would not work if it was the main fusible link. If the battery just came off the shelf there may be enough juice in that battery to power a few lights and horn but maybe not enough to crank. Without a meter you're stabbing at things. One could check for battery voltage at the starter terminals to see if there's anything there on the main or solenoid feed. As for the anti theft, I don't know much about that for Subaru, but wouldn't you expect horn & flashing lights if it had been triggered?

 

this is not your year of Outback but the main fuse/ fusible link is not in the fuse boxes, it's attached to the main terminal like this:

 

this is not your year of Outback but the main fuse/ fusible link is not in the fuse boxes, it's attached to the main terminal like this:
View attachment 496448

This is what I'm looking at under hood.

Sorry I can't add more. I was a mek-anik for many years but never worked on Subarus (mostly trucks of all sizes) so while I wonder if you've pooched the electronics if all fuses and fusible links are OK, it would be irresponsible for me to coach you any further with one possible exception. If you think you've tripped the anti theft, I would start researching that if it were me. Hopefully someone who knows the Outback electrical system will chime in.

Thank you... I see a tow truck in my future.

 

Sorry I can't add more. I was a mek-anik for many years but never worked on Subarus (mostly trucks of all sizes) so while I wonder if you've pooched the electronics if all fuses and fusible links are OK, it would be irresponsible for me to coach you any further with one possible exception. If you think you've tripped the anti theft, I would start researching that if it were me. Hopefully someone who knows the Outback electrical system will chime in.

 

Thank You... one more stab at it tonight and then tow truck....

 

According to the 2011 wiring diagrams, if the 120 A main fuse in the engine compartment fuse box is blown, there are still circuits that are powered, including the interior lighting, e.g., the map lights and the ceiling light (when manually switched on), and the horns.

That, of course, presumes the battery is good, and the wiring from the battery to the fuse box is good.

If the interior lighting doesn't work, fuse #10 (10 Amps) in the engine area fuse box should be checked. With the meter, also check to see if there's 12 V at both sides of the fuse. And, certainly, check the battery voltage at the two battery posts, then at the cable clamps.

The FSM doesn't seem to show any fuses (or fusible links) at the battery, as in the photo above, but it wouldn't surprise me if there is.

When the battery cables are connected in reverse, current from the battery has a direct path through the alternator. If (and this is important) the ignition switch was at OFF, most circuits are disconnected, and the remaining ones all have fuses with relatively lower values, so other than blowing fuses, those circuits should be intact. However, the current through the alternator goes through the main 120 A fuse, so it, and the wiring to it, could be damaged. In this regard, the 120 A main fuse, might not have blown, but 100+ Amps might have been going through the wires, and they could be fried. The latter includes the positive wire from the battery positive post to the fuse box and from there to the alternator output post, and, the ground wire from the battery negative post to the body and/or engine.

 

Thank you for your insight. Believe it or not... I do understand. I also feel that I have gotten in over my head with diagnosing and fixing. I can change the ECU but I am not convinced that is the problem. At this time I lean toward a fusible link or the anti-theft. Are there numerous fusible links beyond the engine fuse box? Would the lights, horn, brake lights work if the main fuse or the fusible link before the battery were blown? If the ECU was fried? Dang this is frustrating. (maybe because I'm not a mechanic but a dumbass for getting myself into this).

 

If you have internet access look here to see if it helps. You'll see where main is in under hood box and I see that there is a starter relay fuse in the dash fuse panel

Fuse Box Diagram Subaru Outback (2010-2014)

Fuse box diagram (location and assignment of electrical fuses) for Subaru Outback (2010, 2011, 2012, 2013, 2014).

fuse-box.info

 

I think it would be more reliable to measure each side of the fuse relative to ground and expect to have battery voltage on both sides.

Exactly.

 

Why so complicated?
battery ground to fuse feed side: 12V
battery ground to fuse load side: 0V
conclusion = fuse bad

 

Why so complicated?
battery ground to fuse feed side: 12V
battery ground to fuse load side: 0V
conclusion = fuse bad

The confusion is whether the voltage measurement is done:

• just as you state above (i.e. two comparison measurements taken at both ends of the fuse against the same ground reference), or
• a single masurement taken differentially across the fuse, floating the voltmeter

Either way is valid as long as you maintain a disciplined approach in your measurements and understand the results you are getting. It will matter though how you document the approach to others.

FWIW I thought it was the second approach that was being described.

 

Please let us know how this turns out. Reversing the input voltage on a DC circuit may destroy components downstream of the voltage source without blowing fuses. It is interesting that the horn and simple light circuits may still be working because they are not polarity sensitive. On the other hand, the Subaru's sophisticated control modules may have been fried due to this event. I wish you good luck with this.

 

Shoudn't decent design prevent reverse polarity from destroying things simply by interposing diodes to prevent current flow in the wrong direction? Even better would be a rectifier bridge circuit to make battery polarity irrelevant. Of course, that does cause a small voltage drop, which could be a problem if the battery is almost dead.

 

Where do you draw the line? What technology would we impose to prevent forgetting to torque wheel nuts?

Connecting a battery is very basic stuff and anyone who knows what they're doing AND is paying attention would never do this. I've never connected a battery backwards and I've done it thousands of times. Even if I were to put the positive clamp over the negative post, I'd have no problem because a) I'd see right away that it doesn't fit and b) the ground wouldn't be connected. Ground is off FIRST and on LAST and there are reasons for that. Note that I didn't say "negative" because that is not inclusive enough. The point is, you have to know more about what you're doing besides how to turn a wrench.

 

Where do you draw the line? What technology would we impose to prevent forgetting to torque wheel nuts?

Connecting a battery is very basic stuff and anyone who knows what they're doing AND is paying attention would never do this. I've never connected a battery backwards and I've done it thousands of times. Even if I were to put the positive clamp over the negative post, I'd have no problem because a) I'd see right away that it doesn't fit and b) the ground wouldn't be connected. Ground is off FIRST and on LAST and there are reasons for that. Note that I didn't say "negative" because that is not inclusive enough. The point is, you have to know more about what you're doing besides how to turn a wrench.

I haven't replaced thousands of batteries, but in the many that I've done, I've never done it backwards, nor almost done it backwards. However, not everyone is as brilliant as you or I. In fact, because there is so much wrong data about group number interchangeability, it's very easy to end up with a battery that has the terminals on the wrong sides for your car, thus making it easy to put the battery in backwards, and hence install reverse polarity.

The incremental cost of reverse polarity protection is very small. What about tire pressure monitoring? I have never driven around with underinflated tires, despite hundreds of thousands of miles of driving. Anyone can easily tell if their tires are underinflated. Why bother with that expensive technology?

 

It is hard to know where to draw the line on nanny technology, but nobody is going to suffer from reverse polarity while driving at 70 mph on the freeway, but they could have a blow-out.

The damage from reverse-polarity will cost money but not lives.

Another fine point is that reverse polarity is the result of an inappropriate action, but low tire pressure is usually the result of neglect/inaction.

 

However, not everyone is as brilliant as you or I.

I'm was never brilliant - just schooled and trained.

 

Actually reverse polarity protection, at the kind of currents seen in car batteries (hundreds of amps) is expensive, and difficult to do well.

A full wave bridge by itself will not work: current needs to flow both into and out of the battery, and full wave bridges allow current flow in only one direction. Additionally, the voltage drops would kill the whole calibration of the charging voltage, so the alternator output would need to be turned up.

 

Not necessarily the answer to this post but a simple solution to blown master fuses is to use a circuit breaker that can be reset.

One of the recent “nice” things in the aftermarket automotive electronics space is fuses that turn on an LED when blown, makes it much easier to see which fuse is blown.

Seagrass

 

One of the recent “nice” things in the aftermarket automotive electronics space is fuses that turn on an LED when blown, makes it much easier to see which fuse is blown.

Which, interestingly, brings us back to the discussion on the previous page about whether or not there's voltage across a blown fuse! QED?

 

If you go across a fuse that is blown you are putting the volt meter in series. AFAIC, that makes it a pretty much useless diagnostic procedure in this case. Amp meter - series. Volt meter - parallel.

 

Putting the voltmeter test leads across a fuse places it in series with the source and load, correct. And the reading on the voltmeter will tell you if the fuse is blown once the circuit is energized:

• An intact fuse will only allow a very low voltage across the fuse pins, perhaps 10-20 mV.
• A blown fuse will show the entire 12V across it, unless the load has been blown open, because you have the source on on side of the fuse and the load on the other.

The object of this particular test is not to measure current draw, it's to check the state of the fuse. This is an excellent diagnostic test, and it's just a go / no go kind of thing. The number you get doesn't mean a whole lot beyond the condition of the fuse.

You do understand that a voltmeter's internal impedance is 100's of Megohms to GigaOhms, yes?

And also that the ammeter function on a voltmeter is nothing more than an internal resistive shunt inside the case of the voltmeter that the voltmeter bridges across, and by knowing the value of this shunt it then converts the voltage it internally measures across this shunt into amps using Ohm's law?

If you follow me on these two concepts, simply mentally replace the internal resistive shunt with the fuse, and you'll grasp the means by which a bridging measurement can determine the condition of a fuse.

 

Whatever works, as long as you know what readings to expect from your meter

Checking Fuses with a Meter

 

Was there any resolution to this after the tow truck was called?