Ok, this is my first post so please be gentle. I have a 2009 Fit Sport, m/t without navigation. I have owned it since 2013 and it is my daily driver with 139K ALMOST trouble-free miles. I finally decided to do a bit of an audio upgrade. So, I Dynamatted all 5 doors and installed a Pioneer head unit, 4 Rockford separates, a Rockford T400X4AD amp, and a powered Rockford 300 10 subwoofer. Just two amps, and small ones at that....I really thought that even the stock electrical system could handle them. All amp wiring is 8 gauge, originating from the positive lead on the battery. All grounds were short and to the body. All connections were either fastened with the methods provided or soldered and heat-shrunk. Battery posts and connections are spotless and very firmly tightened.
My alternator is the original, which showed on my diagnostic computer to be putting out 13.7v-14.5v .....13.7 was with the headlights and foglights on, heater fan on full blast, and the stereo at full volume. The only way I could get the headlights to flicker SLIGHTLY was to turn the subwoofer volume to 100%, waaaaay beyond what the adequate setting is.I still have the standard size battery, but it was fully charged and read 12.53V.
The system performs FLAWLESSLY. It sounds SPECTACULAR, and everything else on the car performs perfectly. After doing some measuring/tuning, I drove it to work the next day. Everything was perfect, and I was seriously rocking out with the volume around 85%, doing 85 on the tollway.....and the motor promptly DIED and my headlights VANISHED. I pushed in the clutch, maneuvered to the shoulder, and tried to assess what was happening.
1. Headlights, interior map lights, door locks, heater fan and rear defroster were non-existant. However, my gauge cluster had full lighting. The starter cranked like it had a brand new battery, but apparently the fuel pump was shut off as well as it would not fire. I DID have wipers, washer, and hazard lights.
So after calling the tow truck and climbing over the back seats and trying to get to the spare tire well to get the damn eye bolt for the front because the f#$&ing doors were locked, I tried starting it again...same thing. Like I said...the starter sounded PERFECT, and my gauge cluster was fully lit...but no motor, heat, radio, doorlocks.
As the tow truck was pulling the car up the flatbed, the headlights popped back on. I climbed up and turned the key and the car started PERFECTLY. All functions worked perfect. I had it towed anyway, as I didn't need to be stranded twice on my way to work.
I got the car home and checked EVERYTHING. I put the scanner on the OBDII port and everything looked perfect. NO CODES flashed. Voltages were all good. So, on Saturday, I drove around the country by my house, trying to get the failure to happen again. I had my wife with her truck available to tow me home, and I had my diag scanner hooked up. Had the volume cranked on the system, and sure enough, after about an hour and hurting eardrums...it failed again. Once again, No warning....same thing. NO flickering headlights, NO weak power output from the stereo....NOTHING. But this time I realized the OBDII port had no power either. Wife towed me home. Battery had 12v still. I hooked my battery charger up to it, and after about 5 minutes, the car came back to life. Once again, no codes flashed.
Ok. Now before I put a 51R battery in and get my alternator hot rodded, I want to know what the heck is going on, and if these things will even help. I've had weak batteries before, I've had alternators go bad, but they always have a bit of a "warning". It feels like my ECM is doing some crazy stuff, but my battery isn't dead or even seem to be dying.....and my alternator output appears to be well within specs.
Needless to say, I'm driving my truck to work because I don't trust the Honda even with the stereo OFF at this point. It runs and drives perfect, but I really don't need to be stranded again with no warning until I can get this resolved. Any ideas or help is VERY welcomed! Thank you in advance!

 

That sounds scary. Obviously you need to use extreme caution for testing due to electrocution danger and risk of power out on the road. You might have a professional check this out also if you don't feel issue is 100% resolved.

As gremlins started happening after the stereo install, that seems like a logical place to start.

- Automobile computers can be fussy about proper power. The Fit battery and alternator are "undersized" so one possibility is that running the big custom audio system for a while pulls current and voltage down such that one or more computers are stumbling.

- I would run voltage drop tests (under load) with the car running, whole audio system running and headlights and fans etc. This gives you some proxy of resistance issues and power around various systems.With a fast DMM you might see some serious drops that make the issue obvious; a slow DMM might completely miss the max and min. I suppose major drops or very spiky voltage could cause problems. High voltage can also cause problems.

- Typically grounds are an easy culprit in tweaks but I'm not so sure in this case. Still worth reviewing. Did you grind your body grounds to bare metal and test resistance on all new grounds? Did you test all your positive wires? Did you test resistance on the factory connections at battery, grounds, alternator, fusebox (under load)? Did you check all major harnesses are well fitted, particularly at fusebox and computers?

- I suppose the subwoofer could be drawing the most power and is the driver for your issues. Disconnect it and run your test extensively, beginning in the driveway. Maybe disconnect the whole system and see if car returns to normal as a start then slowly begin connecting systems. . .

- We have problems with a relatively new 151R battery in cold weather starting in a stock car, even if we "smart charge" overnight on a weekly basis. So I don't think the battery is up to the task with bigger audio. Not sure a small bump to 51R battery gets you enough juice. And that tiny alternator might be an issue you can mitigate by trickle charging the car overnight several times a week/month. The car stereo forums will have more helpful information.

 

 

Here comes the dumb guy that knows nothin about audio systems.
immobilizer?
tap into anything using a heavy gauge going to a somewhat lighter gauge, even by one size?
did you install inline fooses?
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hahaha. Warning. Not dumb and knows a lot.

 

All wiring (except speaker and RCA) is 8 gauge. All grounds were cleaned with steel wool, secured, and coated in rubber sealant for protection. I used factory grounds, the Fit has plenty of them. My system has 3 60A fuses....one approximately 1" from the battery post and 2 60A in my distribution block. There is no indication of ground loops, no alternator whine, no indication of anything improper.

 

Unplug the amp to see if the issue goes away. You might be killing the battery like Jerry said if the load is not being detected.

 

You're a gent. I swear this is the classiest enthusiast forum there is. Put a lot of work into this one, man, theres just no easy answers from our end. you probably know exactly whats up and just need a good long break for it to come to mind.
from our end though!: Disconnect the setup and verify the fault. If it persists, well, you know. If it doesnt, we're going to need pictures of eeeverything you did.
My headlights dim at idle with a brand new battery when a fan kicks on. ~15amps. No electric mods whatsoever.

the only possibilities here are excessive draw (how many amps does the system pull?), installation error (still wondering if your immobilizer got touched somehow), or unrelated electrical failure.

Can tell you put some serious effort into this. we've got you.

 

I DID notice that there was a pronounced voltage drop when I turned the light switch on. It was a bigger drop than turning on the AC, bigger than turning the radio on/off. The switch WORKS just fine and is still pretty "snug"...no sloppiness in it at all. The drop was the same with or without the foglights. Since my battery is over 4 years old, I think I'm going to go ahead and put a 51R battery in, and maybe invest in a HiPo alternator later on.
I know my system is taxing the factory electrical system. What I want to know is why the thing stopped completely dead and did NOT issue ANY codes... the battery light did not come on..."check engine" light didn't come on.... the lights didn't flicker or dim....anything like that to denote a weak charging system.

 

Brown Outs the effects can be unpredictable I think ​​​​​​it would depend on what could handle the drop in voltage. Some devices, sensors, maybe the ecu itself, may be weakpoints for heat. Certain failures may not trigger a CEL.. with new tech its harder for me to say. But on slightly older stuff your throttle position sensor may not trigger a CEL, so suddenly your ECU doesnt know how much fuel to inject and that can cause some rough riding! There are several systems in any given car that just arent on the list for a CEL. Most are mechanical failures I'd imagine, but some electrical. Chasing down exactly what failed for yours would be toooo risky because you sure dont want to replicate this fault further for risk of causing damage to electronics.

SO! If you wanna drive your car in the interim, just unhook the system. If it *does* still have issues then I'll crack open the manual and we'll start troubleshooting component failure based on fault and keep going down the list until we get lucky

 

I still think this is the problem. As the voltage drops, some systems will start to fail/shut down. But not all at the same time or even in the same order. Some can probably run at very low voltage which can make diagnosis frustrating.

I don't know what the immobilizer disables so can't help there.

Your first post indicates what systems may be dropping out and what systems could handle the reduced power. Look through the electric schematic to find any common links (just looking at the fuse labels might give you a clue).

 

I was hoping that this would be a common problem with people putting big stereos in their Fits and there was a well known fix for it.....no such luck LOL! I think I am gonna splurge on a big amp alternator and a 51R, and see what happens. I have been reading about the dual-mode electrical system, and all the problems associated with that.....Good Lord. I'm only running 700 watts with pretty efficient amps!
i am also going to get a jump start pack to keep in the Fit so if this crap DOES happen again I hopefully won't need a tow truck.
What a guy has to go through to have loud jams on the way to work!

 

Before you do all that. Get a capacitor and put it near the battery. Likely don't need more than 1 farad.

 

Scoured the internet when researchin this. read on another forum that a capacitor is a mistake. Dont comprehend electrical near well enough to know, but I'd definitely read up to see why anyone at all would say its not cool, just to be sure.

instead of upsizing your battery, you could add a 12v atv/atc battery.. they weigh about 7 pounds, cost 20 bucks (or 60 if you wanna be sure you're getting a real 'murican made AGM) on amazon and just run it inline.. big ol diesels run two I think, tanks run 6 inline.. someone else can chime in if its a bad idea. The AGMs (absorbed glass mat) are spill proof so you could mount it however the heck you want and still keep your current battery, plus pick how much juice you want to add.

 

I've heard of this problem a few times before. Typically someone will be jamming to a song with some bass and each hit of the sub will cause headlight dimming.
In other cases the car computer loses enough voltage to stop the car and often won't record a code. In any case a cap won't hurt anything and is pretty cheap. I used to use an expensive 0.8 farad one in my car many years ago. Now they have like 5 farad ones cheap.

Also it could just be a bad amp install with it not isolated enough from the chassis, picking up noise in the cars electric system.

 

There is ZERO noise. It is NOT a bad install. The system works incredibly, especially with the soundproofing. I really think after all the pondering and scanner-ing that I had a voltage drop that was enough to freak the ECM out but not enough to "register" and start shooting off trouble codes. Bought a 51R yesterday, and if I have any time this weekend I'm gonna install it and put in earplugs and test it out. I have had some experience with capacitors, and I may put one on after the battery swap.

 

Awesome info I really appreciate it. This thread may well be the first time I've heard the word "farad". Lots of respect for electricians.

Sorry for pickin' at the install, my friend. Tons of guys get in over their head with electric stuff (myself included), its so incredibly common that it's gotta be everyones first assumption. I'm glad you've got the thing all squared away and am confident it'll thump for yuh.
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But I'm an accountant

 

A larger battery and alternator are what is needed. The current supplying device (alternator) is what is struggling to provide sufficient power. Now you added a capacitor and it needs to now supply power to that also. Doing a big 3 ground upgrade would be beneficial.

How big of a system did you instal?

 

A capacitor doesn't use power itself. It builds it up and supplies it when the voltage dips. Effectively smoothing out ripples in the power.
Clean power is what the car computer wants.