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I saw another thread on this topic from back in 2016, but I was not aware of the issue until it was too late. This is actually on my 2015 Mazda 6, but it shares the same RBCM (KD45675Y0G) and wiring arrangement. A few days ago, I tried replacing my terrible trunk light with a strip of LEDs, and since this light is switched through the Rear Body Control Module (RBCM), I fried a transistor (MOSFET) inside of it by overpowering the circuit. The symptom of this failed transistor is that the trunk light just stays on all the time and never powers off.

Don't make the same mistake I did, only use a low powered LED if you replace it. The stock bulb is rated at 3W, I would suggest not exceeding that number since I have found several people that have fried theirs as well.

Below are some photos of the inside of the RBCM - one of the burned up chip, and the other of the chip removed and cleaned a little (and poorly at that). I can't see the writing on the MOSFET, but if someone, someday, is brave enough to open up their good RBCM, I might try replacing it with a bigger MOSFET, but there's some cratering of the board, so who knows - I'm not super skilled on a soldering iron.
 

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Here in a german forum you can see, that at the 6-pin chip is written "ZX 3 K4".

Here at cx-5.ru they might have identified the 6 pin MOS chip. For translation use e.g. google translator or an add-on in chrome browser - works well for me, as I do not speak/read russian.

It is mentioned that it could be this chip: 6A8 SOT23-6 ZXMN6A08E6TA. Aliexpress-Link

Additional info: Older RBCMs (e.g. CX-5 before 2015) have not a 6 pin chip, but a 4 pin-chip (3pins on one side and 1 big pin on the other) - this was most probably a 2SK2857 from NEC.

Good luck and please inform us later, what chip you used and if it worked well.
 

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Just look for an used RBCM module on ebay. I "burned" mine few years ago when I was trying to change the trunk light (there's no fuse for that light... did short circuit and... blame on you mazda!).

But it only took me 50€, 30 minutes of work, and ODB2 interface to program correctly the new module.
 

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Discussion Starter #5
Here in a german forum you can see, that at the 6-pin chip is written "ZX 3 K4".

Here at cx-5.ru they might have identified the 6 pin MOS chip. For translation use e.g. google translator or an add-on in chrome browser - works well for me, as I do not speak/read russian.

It is mentioned that it could be this chip: 6A8 SOT23-6 ZXMN6A08E6TA. Aliexpress-Link

Additional info: Older RBCMs (e.g. CX-5 before 2015) have not a 6 pin chip, but a 4 pin-chip (3pins on one side and 1 big pin on the other) - this was most probably a 2SK2857 from NEC.

Good luck and please inform us later, what chip you used and if it worked well.
Wow, that's some top quality stuff you found! Now that I see it's an N-channel with the top four pins on drain, I can sift through some spare parts and see if I have something that matches closely enough to swap in. Excellent post!!
 

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Just look for an used RBCM module on ebay. I "burned" mine few years ago when I was trying to change the trunk light (there's no fuse for that light... did short circuit and... blame on you mazda!).

But it only took me 50€, 30 minutes of work, and ODB2 interface to program correctly the new module.
I ordered one already in case my attempt to repair fails.

How did you program the RBCM? Via OBD/Forscan? Copying a backup of your old RBCM config to the new RBCM?
I've read in at least one place that there's no VIN info on the RBCM. I also don't see an EEPROM on the board to store the data, so I'm going to bet on no programming necessary. But if there is, I have a new J2534 programmer already in the mail and a FORSCAN extended license ready to go.
 

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@alej0 : How did you program it?

@fivil : Whats the status of your repair? Did it work? How?
Ended up buying a used one off eBay, couldn't find any suitable spares in my parts bin. The one I bought is a slightly different part number with a slightly different board design (it had a 4 pin FET). No programming was necessary, the RBCM is not VIN matched as far as I can tell.
 
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