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2015 Mazda6 won't start (but has power) after new battery

13K views 8 replies 4 participants last post by  tickerguy 
#1 ·
The car: a 2015 Mazda6. I can’t turn up anything specifying GT, et cetera (without a VIN search, I guess), but she’s a sedan and seems to have the default engine specs…?

The problem: She won’t start; just clicks (once) as everything lights up.

The time frame: Since I dropped a new battery in a few days ago, stone-ignorant of the need to drain the ECU. I also tried, initially, to put the battery in backwards, frying fuses (which I’ve since replaced).

Yes, in hindsight, I KNOW that was stupid! I’d assumed that Western batteries and Japanese would have terminals on the same side. Go ahead and laugh. :laugh2:

The location: Arkansas (the mid South).

The notes: I don’t begrudge dealership employees a living (at all), but taking her in now could take a painful bite out of the family Christmas. That—and conviction that I made a mess of my wife’s car, so I need to clean it up—is why I’m desperately hoping to fix it myself.

A check-power-steering dash icon lights up at start now, too (and wasn’t before). Not certain why it’s appearing, but I suspect that it’s a clue.

Research suggests possible ECU damage, but I don’t see anything that clearly looks like an OEM ECU under the hood. I haven’t found much that’s helpful on the Web, either (after multiple attempts). Is it in the interior, maybe on the driver’s side? How much would I have to take apart to reach it?

I did read where someone pulled an ECU fuse and replaced it, but I can’t find one labeled “ECU” in the hood or interior fuse boxes’ lid diagrams…?

Any/all constructive suggestions are welcome. Thanks for reading this far!
 
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#3 ·
If you connected the battery backwards (positive and negative reversed) odds are you've destroyed module(s) in the vehicle. Maybe all of them. Check all fuses; you might have gotten VERY lucky but I wouldn't take a wager on it and you don't want to know exactly how bad this could be in terms of dollars.
 
#4 ·
Your battery supplies 12.5-14 volts to the system. The computers on your car use anywhere from 6 volts to 6 millivolts. They do this by using voltage converters, but when you hook the battery up backwards you bypass those converters. It can fry your computers very quickly.

Get a scan tool and see what the check engine light is. Maybe all that power just blew a small component somewhere. Or, you may need to replace an entire ECU unit. Or, worst case scenario, you damaged one or several of the dozens and dozens of sensor relays throughout the vehicle, which would practically total the car.

Scan tool first, then take it to the dealership.
 
#7 ·
Your battery supplies 12.5-14 volts to the system. The computers on your car use anywhere from 6 volts to 6 millivolts. They do this by using voltage converters, but when you hook the battery up backwards you bypass those converters. It can fry your computers very quickly...
Thank you for the informative post, Iamadoorknob! I'm trying to keep up the hopes... but I'm hearing you.
 
#8 ·
I'm HOPING to at least reduce the cost of a dealer visit, if it can't be avoided--and I've pulled all the smaller fuses. Do I need to replace the fatter ones, too?

Any idea which module(s) would affect power steering? Where would they be?

I'm guessing that I'd be out over a grand if I'd taken her in already...?
 
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