BCM?

It sounds like you had a voltage surge due to the amp and blew out fuses. lets start by using this guide and checking the fuses for power the fuse locations are blow.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Check out the diagrams (below). Please let us know what you find.

I already tested all fuses from the engine bay and interior side panel with a multi-meter, all of them are fine. I went ahead and tried to remove plugs from the BCM (body control module) and tested the grounds. All ground wire going the the BCM works. excepts:
- Steering angle sensor ground
- Ambient temperature ground
Both systems are not working, so I guess it’s a loose ground from the bass somewhere. I looked up 4 different grounds near the BCM but all of them all correctly connected and when tested with a multi-meter they all show small resistance.
I don’t really know how to find the ground that as a problem since there are a bunch of them all around the car.

Update:
I just tested the ground wire from the hazard light button, there is quite a lot of resistance from the ground cable of the button to the chassis.

I just noticed, the pictures you provided are for the 2014-2018 version of Mazda 3. Mine is 2011 so 2010-2013 version.

Okay, cool thanks. here is the ground distribution wiring diagrams so you can test them and it give the locations of the grounds as well:

https://www.2carpros.com/articles/how-to-check-wiring

Check out the diagrams (below). Please let us know what you find.

I just tested most grounds related to the problem, all of them are correct. I did another test, I tried to test the resistance in the hazard switch, to see if ground was getting there. There is a resistance but a pretty big one. After that i tried to put a wire into the ambiant air temperature sensor ground wire on the bcm, while the connector was plugged to see if ground goes threw. It does but with a big resistance as shown in the picture, all my test were going back on a working body ground. Here is a picture of the multimeter.

I’m starting to think that it is a bcm malfunction. But I want to be sure before ordering another one...
Thanks for your help! Very appreciate it!

Yep, I was thinking the same thing. to be sure we can do a CAN scan here is a video:

https://youtu.be/InIlnsjOVFA

Here are the instructions and locations of the BCM so you can replace it. Check out the diagrams (below). Please let us know what you find.

Hi, I just received my new obd scanner, I was able to pull off the code U0140: lost communication with bcm. I went ahead I looked some forums. It seems that the bcm is rarely the problem with this code, it is most probably:
Bad ground
Short in circuit
Another module controlled by the bcm that is malfunctioning.

What do you think is most probable? Thanks

Yes, it could be that's why the CAN scan is such a good thing. Here are the wiring diagrams for the BCM so you can see how it works while testing the powers (fuses) and grounds. Check out the diagrams (below). Please run this test and get back to us.

Thanks, what are the j/c c-XX in the diagrams?

JC is junction connector, and CXX connector - number

Everything looks fine, I took a 2 week vacation and when I came back, I did another code read. There was a new one: u3003:16
I was not able to find good information around the web, if you could help me find what it means. :)

U codes are communication errors. BCM not communicating in most cases. I would try to replace the BCM or do a CAN scan to confirm.

Do I need to go to a mechanic to do a can scan or I can do it with my scan tool? Here is some pictures of the app am using and the capability of it.

That is for PCM only, the CAN scanner looks like this for 59.00 on Amazon:

https://www.amazon.com/gp/product/B007XE5LTG/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=2carprcom-20&creative=9325&linkCode=as2&creativeASIN=B007XE5LTG&linkId=14d1dd6528325a6a988e7520492d5724


Let me know.

Just went to the junk yard and picked up a BCM. Solved all problems except rear trunk open button and rear wiper, but it’s probably due to the used BCM being in a sedan. Thanks for all your help!

Glad you could get it fixed, that kind of problem can be tough. Please use 2CarPros anytime we are here to help.