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DIY: 05 BL/BP stereo/heat switches/mirror switch illumination repair (BIU repair)


SubOperator

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Disclaimer: In addition to functions of lighting described below, BIU is responsible for a lot of other things in the car including recognizing immobilizer chip in your car keys. If you damage BIU and end up getting it replaced, you'll have to reprogram the car keys at the dealer to make them work with new BIU. Do not attempt this repair if you are not experienced soldering fine electronics. You've been warned.

 

 

Subaru BUI repair. BL/BP BIU part # is 88281AG10A.

 

 

History:

 

 

A while ago during a prolonged day out in the open field on very hot day I turned the lights on (I had my DRL disabled at the time) and noticed some smell of burning plastic that quickly went away. Everything seemed to work fine, the outside check confirmed the lights being on, so I thought the smell came from some one else's car. Lights were turning on and off without issues, stereo and clock worked, so I didn't get too concerned. Only when I was leaving for home that night I found that the night illumination on the stereo was not on, so I couldn't see any knobs and buttons in the dark. The clock and instrument cluster illumination was on and could be adjusted, and my first thought was some connector got loose and I simply need to plug it back and everything would be fine.

 

 

Investigation:

 

 

What I found was this: illumination was completely lost on stereo (including climate control), heater switches and mirror switch (irony is the illumination adjust knob is there, heh...). Illumination worked and could be adjusted at instrument cluster and clock.

 

 

According to Illumination wiring diagram from Opie's vacation pics, the three units with broken illumination were wired from BIU's pin A5, and the clock and instrument cluster seem to get the illumination level commands from BIU via UART or CAN as I was not able trace same illumination wire to them. This explained why clock and instrument cluster had illumination working and stereo/heater/mirror switches did not. Moreover, according to wiring diagram, illumination circuit was getting straight battery power on feed and was draining to BIU's A5 pin. 12V were coming from battery properly, but same 12V were on draining pin, and after I disconnected BIU I connected that end to ground and stereo/heater and mirror switches were all lit, but could not be adjusted. It looked like BIU was the problem. Plugging in another BUI that I acquired from LGT member confirmed this – the stereo/heater switch/mirror switch illumination came right up and worked properly.

 

 

Repair:

 

 

Subaru BL/BP BIU part # is 88281AG10A.

 

http://legacygt.com/forums/attachment.php?attachmentid=110558&stc=1&thumb=1&d=1465399645

 

Taking out the BUI: it is located right under the steering column and the holding bracket is bolted to the steering column. You'll need to take off couple of plastic panels to gain access to two bolts that hold the bracket. It is going to be blind job – but doable. 3/8 ratchet with 10mm socket worked great for me. Do not try to pry the BUI module from the bracket – you don't need that to get the PCB out to begin with, and most likely you'll damage the bracket or casing or both. Take your time and undo the two bolts and take the BUI with the bracket out. First undo two plastic clips holding the harnesses on the sides and three connectors, use flat head screwdriver for side clips.

 

Now, the BUI PCB is fixed in BUI casing with some silicone that acts like glue, and makes it pretty much impossible to pry out the PCB (asking me how I know). I used heat gun to warm the casing and soften the silicone – then I was able to slowly pry out the PCB using two screwdrivers. The silicone is in three spots – all of them on the back of the casing, on the other side from connector, in two corners and in the middle.

 

 

When you take the PCB out, it is going to look overwhelming (at least for a guy like me) to take on it.

 

http://legacygt.com/forums/attachment.php?attachmentid=110559&d=1326685385

 

Fortunately, when I was googling “Subaru BUI repair” I came across a post from Forester owner who had taken on BUI he fried and was able to fix it. Here is the link to that post:

 

http://www.subaruforester.org/vbulletin/f85/body-inegrated-unit-dome-dimming-circuit-data-repair-83167/

 

 

Forester owner fried his car's dome light dimming circuit and found that broken part was a MOSFET transistor NEC 3377 rated at 30W, his solution was to replace it with pin-out compatible NTE 2987 MOSFET that is rated at much more assuring 100W.

 

 

Well, guess what ? The same MOSFET 3377 that the post above is referring too is found in BL/BP BUI ! Ours actually has 2 of them mounted on PCB. And while pin A5 on Forester BUI drives the map lights, on Legacy BUI the A5 pin drives the stereo/heater/mirror switches illumination; the second 3377 on BL/BP BUI drives the map lights and it is wired to pin B3.

 

http://legacygt.com/forums/attachment.php?attachmentid=110560&d=1326685385

 

Second 3377 on BL/BP BUI drives the map lights and it is wired to pin B3:

 

http://legacygt.com/forums/attachment.php?attachmentid=110561&d=1326685385

 

As suggested, I got the replacement MOSFET NTE 2987 (two of them) and replaced the 3377 on the back of PCB with 2987. I got them online, with shipping it amounts to <$20 for both.

 

http://legacygt.com/forums/attachment.php?attachmentid=110562&d=1326685385

 

I had to get creative due to sheer difference in sizes of two parts, so I found a different mounting location – see pictures. I admit that having a heat sink is an overkill but I had some old VGA cards laying around so I fabricated two small heat sinks.

 

http://legacygt.com/forums/attachment.php?attachmentid=110563&d=1326685385

 

http://legacygt.com/forums/attachment.php?attachmentid=110564&d=1326685385

 

 

Warning: the mount locations I used for both replacement 2987s use existing holes in PCB with ground – I used insulating plastic washers and stands. If you select the same locations, make sure you insulate the drain of 2987 from ground similarly to what I did – otherwise you do some damage to 2987 or most likely your BUI PCB that will be much harder to fix from there. You've been warned.

 

 

So replacing the 3377 on the back of PCB brought my stereo/heater/mirror switch illumination back to life. With that, and knowing that the B3 pin from map lights uses the same idea of floating positive ground and has identical 3377 part I went and replaced the other (still working) 3377 with another 2987. I plan on using the map lights at some point to hook up either puddle lights or foot well lights (or both), so I decided to beef BUI up while I was there anyway. Everything worked fine with second 2987, my dome and map lights dim properly.

 

http://legacygt.com/forums/attachment.php?attachmentid=110565&d=1326685385

 

http://legacygt.com/forums/attachment.php?attachmentid=110566&d=1326685385

 

 

Other findings:

Now , if you look at the picture of PCB where the B3 connected 3377 is located, you can see empty place and contact pads that look exactly like another 3377 was meant to be there. I think this was a provision for some option that USDM Legacy/Outback do not support but BUI could – puddle lights, foot well lights, may be map lights dimming from the factory ? I didn't spend time trying to figure out which connector/pin is goes to though, leaving it to you to find out.

 

 

As far as BUI connectors go – the A5 pin is BW (black with white strip) wire on largest connector, B3 is brown wire on the smaller connector on the apposite side from A connector. Wiring/pinout for connectors and BUI can be found in Opie's vacation pics (Sections “Illumination and Clearance”, pages 5001-5006, BUI pinout is (strangely enough) in “Lan System Diagnostic” - “subaru select monitor” section).

 

http://legacygt.com/forums/attachment.php?attachmentid=110567&d=1326685433

 

http://legacygt.com/forums/attachment.php?attachmentid=110568&d=1326685433

 

 

Hope this helps. I simply enjoy having my BP's cabin glow red again in the dark. Loving this car ...

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Edited by SubOperator

2005 LGT Wagon Limited 6 MT RBP Stage 2 - 248K

2007 B9 Tribeca Limited DGM - 258K

SOLD - 2005 OB Limited 5 MT Silver - 245K

SOLD - 2010 OB 6 MT Silver - 205K

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  • 11 months later...

Very helpful post. My dome light wont turn on with my doors because i added some underground light kit to legacy and i think i burnt it. Having a baby and buckling her in at night without the dome light makes it very difficult. Might have to tackle this project to get it working again.

 

Great post BTW!

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thanks, glad you find it useful. I did replace the second working 3377exactly because I want to add some puddle lights and stock part is almost maxed out as it is.

2005 LGT Wagon Limited 6 MT RBP Stage 2 - 248K

2007 B9 Tribeca Limited DGM - 258K

SOLD - 2005 OB Limited 5 MT Silver - 245K

SOLD - 2010 OB 6 MT Silver - 205K

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  • 9 months later...

Hi!

I just got a 2005 Subee Legacy Wagon, W/Auto.

My console lights were the heater control is don't work, those red backlight ones.

The dimmer for the instrument panel also doesn't work, but I still have lights, but low.

And I don't have any working rear speakers!

My electronic rearview mirror does work !

Could this be same problem ?

 

Many thanks, SubeeTedV

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  • 4 weeks later...
  • I Donated

Fixed my dome light!

 

Interesting fact -- you don't have to desolder the original MOSFET. Just solder wires onto each of the pins going into the PCB, and then another wire onto the metal part on the back of the MOSFET (closest to the pins for the harness connectors).

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Fixed my dome light!

 

Interesting fact -- you don't have to desolder the original MOSFET. Just solder wires onto each of the pins going into the PCB, and then another wire onto the metal part on the back of the MOSFET (closest to the pins for the harness connectors).

 

I wish I had thought of this...I accidentally ripped one of the pads off the circuit board when I desoldered the original MOSFET and now have nowhere to attach the new one. :(

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Fixed my dome light!

 

Interesting fact -- you don't have to desolder the original MOSFET. Just solder wires onto each of the pins going into the PCB, and then another wire onto the metal part on the back of the MOSFET (closest to the pins for the harness connectors).

 

It'd be great if you could attach any pics so other can do the same. And fill us in on your illumination project!!!

2005 LGT Wagon Limited 6 MT RBP Stage 2 - 248K

2007 B9 Tribeca Limited DGM - 258K

SOLD - 2005 OB Limited 5 MT Silver - 245K

SOLD - 2010 OB 6 MT Silver - 205K

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Share on other sites

I wish I had thought of this...I accidentally ripped one of the pads off the circuit board when I desoldered the original MOSFET and now have nowhere to attach the new one. :(

 

I didn't forget about high-res pics for you, just didn't get to main PC where I have them....

2005 LGT Wagon Limited 6 MT RBP Stage 2 - 248K

2007 B9 Tribeca Limited DGM - 258K

SOLD - 2005 OB Limited 5 MT Silver - 245K

SOLD - 2010 OB 6 MT Silver - 205K

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  • I Donated
It'd be great if you could attach any pics so other can do the same. And fill us in on your illumination project!!!

 

I'll have to set aside some time next weekend to take pics. I'm attaching the schematic for my illumination project.

1604624823_cominghomeretainedpower.thumb.png.4d337b0ea48139961e9162737ae318d2.png

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I wish I had thought of this...I accidentally ripped one of the pads off the circuit board when I desoldered the original MOSFET and now have nowhere to attach the new one. :(

 

Hi-Res pics sent! Hope they will help.

2005 LGT Wagon Limited 6 MT RBP Stage 2 - 248K

2007 B9 Tribeca Limited DGM - 258K

SOLD - 2005 OB Limited 5 MT Silver - 245K

SOLD - 2010 OB 6 MT Silver - 205K

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  • 2 years later...
  • 1 year later...

OK, the drain is the center pin, so what is the pin that the gray wires are attached to -- ground? The one that's done for B3 is clear since all the original mounting pins are used, but the termination of the gray wire at the board on A5 is really difficult to see. It appears those tiny holes in the board have metal rings, so I'm guessing that metal is a ground?? I know very little about circuit boards and I'm not clear on what SubOperator did with that one gray wire, instead of running it around to the back of the board and connecting it to the existing pin.

 

The datasheet for the NTE 2987 shows that pin as being "source", which doesn't help much.

 

If anyone can clarify this, I would appreciate it.

Edited by axisofevol
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  • 10 months later...
  • 2 years later...
Fixed my dome light!

 

Interesting fact -- you don't have to desolder the original MOSFET. Just solder wires onto each of the pins going into the PCB, and then another wire onto the metal part on the back of the MOSFET (closest to the pins for the harness connectors).

 

Can you elaborate please? which pins go to where? Thanks.

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  • I Donated
Can you elaborate please? which pins go to where? Thanks.
Left pin to left pin, center pin to center pin, right pin to right pin.

 

The MOSFET has three pins and you're basically connecting the new one in parallel to the old dead one.

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Left pin to left pin, center pin to center pin, right pin to right pin.

 

The MOSFET has three pins and you're basically connecting the new one in parallel to the old dead one.

 

Simply put, i can do that... Thank you

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