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BCM?

Tiny
CEDMAC
  • MEMBER
  • 2011 MAZDA 3
  • 2.5L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 80,000 MILES
Hi,

Yesterday, I was listening to some music with some friends in my car. I installed a new amplifier to finish my setup about 3 weeks ago. After my friends were gone, I left my car running for 2 minutes without being there and when I came back, these following symptoms appeared:

Traction control light
Power steering light (it still works fine)
Parking Brake light
No A/C, but the button turn on when I press
No power lock doors
No rear wiper
No ambient air temperature sensor
No day/night sensor for the headlights
No turn signals
No hazards

I don’t know what it could be, I changed the battery about 1 week ago because the other one was dead, I did replace the positive connector to be able to plug the amplifier correctly.

Could my sub-woofers have loosen a ground connector somewhere?
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Wednesday, July 24th, 2019 AT 2:50 PM

16 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,320 POSTS
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.
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Saturday, July 27th, 2019 AT 12:48 PM
Tiny
CEDMAC
  • MEMBER
  • 12 POSTS
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.
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Saturday, July 27th, 2019 AT 4:22 PM
Tiny
CEDMAC
  • MEMBER
  • 12 POSTS
I just noticed, the pictures you provided are for the 2014-2018 version of Mazda 3. Mine is 2011 so 2010-2013 version.
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Saturday, July 27th, 2019 AT 10:33 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,320 POSTS
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.

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Sunday, July 28th, 2019 AT 11:45 AM
Tiny
CEDMAC
  • MEMBER
  • 12 POSTS
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!
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Sunday, July 28th, 2019 AT 7:32 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,320 POSTS
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.
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Monday, July 29th, 2019 AT 10:09 AM
Tiny
CEDMAC
  • MEMBER
  • 12 POSTS
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
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Tuesday, July 30th, 2019 AT 12:13 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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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.
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Tuesday, July 30th, 2019 AT 11:04 AM
Tiny
CEDMAC
  • MEMBER
  • 12 POSTS
Thanks, what are the j/c c-XX in the diagrams?
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Wednesday, July 31st, 2019 AT 1:01 AM
Tiny
KEN L
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JC is junction connector, and CXX connector - number
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Wednesday, July 31st, 2019 AT 11:50 AM
Tiny
CEDMAC
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  • 12 POSTS
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. :)
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Wednesday, August 21st, 2019 AT 8:54 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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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.
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Thursday, August 22nd, 2019 AT 9:24 AM
Tiny
CEDMAC
  • MEMBER
  • 12 POSTS
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.
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Thursday, August 22nd, 2019 AT 10:10 AM
Tiny
KEN L
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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.

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Thursday, August 22nd, 2019 AT 11:29 AM
Tiny
CEDMAC
  • MEMBER
  • 12 POSTS
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!
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Sunday, August 25th, 2019 AT 5:02 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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Glad you could get it fixed, that kind of problem can be tough. Please use 2CarPros anytime we are here to help.
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Monday, August 26th, 2019 AT 12:37 PM

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