BRZ Body Integrated Module (BUI) Question

[RustyS14]

Hey guys, I did a decent amount of research but I can't seem to find a specific answer to my question so I was hoping someone more familiar with these cars might be able to chime in and help me out.

Backstory: I purchased a stock 2013 BRZ about 3 months ago and ever since I picked up the car the courtsey light on the driverside door has been stuck on. It dims a bit with the door closed but remains on whether or not the door is open or closed. I noticed it when I first got the car but assumed it was just a grounding issue somewhere so I wasn't too worried about it and as a temporary fix I unplugged the light so that I wouldn't have a drain on the battery. Anyway yesterday I decided I would try to fix the issue but couldn't find any bad grounds or blown fuses so I started researching the problem and it seems like the issue is with the BUI. The car did have LED lights installed in the doors when I took it apart so I assume one of the previous owners shorted it out on the install but I have no way of knowing.

Now for my question: Does this type of issue with the BUI cause any other electrical issues or is it contained to just the courtesy lighting? The car is obviously out of warranty so I would like to avoid replacing the unit if I can and if nothing else is effected I probably will just install the door reflectors from a FR-S on both doors and be done with it.I haven't noticed any other electrical issues since I got the car so I'm assuming it only effects the courtesy lighting but wanted to double check before I do anything.

[humfrz]

Hello RustyS14 .........

Since I don't know anything about these BUI things ........ I would first attempt the simple approach. That would be take the switch out of the door and make sure it's working properly.......

I'm sure someone, with a more refined approach, will be along soon with some more useful input.


humfrz

[RustyS14]

Originally Posted by humfrz

Hello RustyS14 .........

Since I don't know anything about these BUI things ........ I would first attempt the simple approach. That would be take the switch out of the door and make sure it's working properly.......

I'm sure someone, with a more refined approach, will be along soon with some more useful input.


humfrz

Thanks for the input, I did check the switch with a multimeter and it appears to be functioning properly. I also swapped it out with the one from my friends 2017 STI (they appear to be identical) today just to be sure an no dice. The car still does the same thing.

I've read through these threads and the car seems to have the same symptoms so I'm pretty confident that its the module at this point:

http://www.ft86club.com/forums/showthread.php?t=21537

http://www.**************.com/9-suba...s-doors-2.html

http://www.ft86club.com/forums/showthread.php?t=56856

The only problem is that none of these threads say whether or not the short in the BUI only effects the courtesy lights or if it effects other systems on the car as well. Does anyone know the answer? If it only effects the courtesy lighting I'll just swap them out for reflectors and call it a day, but if this will cause other issues down the road I'll bite the bullet and have the unit replaced...

[humfrz]

Originally Posted by RustyS14

Thanks for the input, I did check the switch with a multimeter and it appears to be functioning properly. I also swapped it out with the one from my friends 2017 STI (they appear to be identical) today just to be sure an no dice. The car still does the same thing.

I've read through these threads and the car seems to have the same symptoms so I'm pretty confident that its the module at this point:

http://www.ft86club.com/forums/showthread.php?t=21537

http://www.**************.com/9-suba...s-doors-2.html

http://www.ft86club.com/forums/showthread.php?t=56856

The only problem is that none of these threads say whether or not the short in the BUI only effects the courtesy lights or if it effects other systems on the car as well. Does anyone know the answer? If it only effects the courtesy lighting I'll just swap them out for reflectors and call it a day, but if this will cause other issues down the road I'll bite the bullet and have the unit replaced...

hmmmm........ so much for my quick and dirty "fix" ......

I went out and checked my 2013 FR-S and either it doesn't have a light in the door or it's not working .... ?? I just appears to have a red reflector.

It looks like if you want that light to work, you are going to have the BCU (BUI - whatever) replaced.

As far as what else that unit may control, I'll summon our resident electrical expert @Ultramaroon for you. He understands stuff like that.

I checked with my buddy Bubba and he says just to cut the wire to that bulb ...... "ya don't need lights in a door anyways".




humfrz

[Ultramaroon]

Unfortunately, there are only two directions to go here. Replace the Main Body ECU, or remove the bulb from the shorted circuit and leave it.

These lights are switched directly by one of the transistors in the module itself. Transistors always fail by shorting. They open if the short allows them to completely burn out.

edit: Oh, forgot to mention that the BCU controls a whole bunch of junk but the failure of that one internal component won't affect anything else.

[RustyS14]

Originally Posted by humfrz

hmmmm........ so much for my quick and dirty "fix" ......

I went out and checked my 2013 FR-S and either it doesn't have a light in the door or it's not working .... ?? I just appears to have a red reflector.

It looks like if you want that light to work, you are going to have the BCU (BUI - whatever) replaced.

As far as what else that unit may control, I'll summon our resident electrical expert @Ultramaroon for you. He understands stuff like that.

I checked with my buddy Bubba and he says just to cut the wire to that bulb ...... "ya don't need lights in a door anyways".




humfrz

Originally Posted by Ultramaroon

Unfortunately, there are only two directions to go here. Replace the Main Body ECU, or remove the bulb from the shorted circuit and leave it.

These lights are switched directly by one of the transistors in the module itself. Transistors always fail by shorting. They open if the short allows them to completely burn out.

edit: Oh, forgot to mention that the BCU controls a whole bunch of junk but the failure of that one internal component won't affect anything else.

Perfect, that was the the exact information I was looking for. Thanks for the help guys!

I was concerned that the short in the module might cause other issues with the car but I feel much better knowing that the problem is contained to just the courtesy lights. I'm just going to grab some FR-S reflectors to replace the lights and be done with it.