When my right brake light went out and the usual troubleshooting resulted in nothing, I got impatient and soldered a jumper from the left brake light to the right. Don't do that.

About 2 weeks later, the left brake light stuck on. While chasing the symptoms in reverse I read that it was either the diode underneath the Body Control Unit (aka BC1, aka General Control Unit, aka BCM, aka... sheesh...) I pulled the diode and tested it... not the problem. Then I found that a whole host of people end up getting the BC1 replaced at a ridiculous $500-$600 for the part and ~$200 for installation and re-programming.

I think you can imagine my response.

Anyway, I took the BC1 apart and found an unpleasant surprise.


Here's a closer shot.


I cleaned it and found that, at a minimum pins 3 and 4 are shot.



A quick search resulted in a Motorola datasheet on MC33286DW.

I looked around on eBay and decided I would rather get a replacement for the entire part (BMW Part 6135-6 935 645) for about $100 instead of shipping an approximate replacement from overseas for $10. My plan is to cannibalize the part which will also give me plenty of options to keep chasing down problems.

I hope this helps.

 

There are a motherlode of them MC33286DWs on that PCB. The burnt mark is right where one of the two incandescent 21W max bulb drivers is. Interestingly the part is designed to be virtually bulletproof - against short, overcurrent, reversed power supply etc.

 

Agreed. The crispy ones go to pins 12 and 31 (right brake and 3rd brake lights respectively. Pin 14 is for the left brake light which is stuck on (was, until I removed and insulated the wire from the light harness.) I believe it goes to pin 17 or 18 of the MC33286DW.


I'm tempted to just remove the chip now before my donor board arrives but I've got other events on my agenda for the next couple of days.

 

It would be a lot of work as there are many of these chips on board. You can always rob from one that functions that are dispensable - like the puddle light etc. But there is no guarantee as you are unsure as what cause the part to fail. Very often failure like this is due to ESD which kills the protection diodes and results in meltdown.

 

Yeah, if you do that at least use an LED bulb so the circuit won't be driving twice the power it was designed for.

Great to see someone actually troubleshoot a problem inside the BC1. Look forward to following this thread.

 

Thanks. Should be pretty easy... I messed with repairing laptop and phone motherboards for a while. Needed a microscope (seriously) to see the SMB makeup. This should be pretty straight-forward.

 

Moving you to the Stock Issues/Problems area.

I never stop being amazed by the knowledge and abilities of the members here.

 

I'm not a patient person. I wanted to see what affect removing the IC would have on the rest of the board's functionality. I have a hot air station so once I heated it up, I globed the leads with flux to keep the board and adjacent components protected.



This is the area of repair after the damaged chip was removed and cleaned. Note that the heat damage actually lifted the trace off the PCB a little. This shouldn't be a problem in the final repair.

 

Too bad you cannot get the chip at reasonably price in US due to NLA. $10 is way too expensive for each IC. I am pretty impressed with how advanced this little car designed in late 90s.

 

Ridiculous, isn't it? I could get them from China for $7 plus S&H (and possibly 2 weeks later) but I'm driving cross country in a week and NEEDED the car in 100% condition.

 

First thing to do was prep the contacts with fresh solder and more flux.



No pictures of the process since I only had two hands and was working in a poorly lit garage. Anyway, I dropped the "new" chip in and started to work the heat around the contacts. Ops check revealed the left brake light wouldn't come on. Added a little solder to the relevant contact and bingo-bango I got brake lights again!!!



PS, anyone want to buy a used BC1 missing a couple of ICs?

 

Forgot to post pics of the three operational lights.

 

Was going over what details may be helpful. I had the hot air and soldering iron set to 425 degrees celsius. I will be doing some experiments with the donor board to see if how the board holds up to higher temperatures. I was being conservative.

 

Congrats with your success in repairing the brake lights.

I am just trying to understand that I followed what you did. If I have not mistaken, you decided to buy a whole used BC module for circa $100, instead of just the IC. I do understand the risk/cost decision that you made. So you pulled a chip off the BC module you purchased to replace the one that burnt out on your factory BC module?

 

Thanks!

That's exactly what I did. I could buy the chip but they all sourced from outside of the US and had shipping times in the "weeks" range. I needed to get this done quickly.

Plus, if no one buys the entire donor BC1 I can pull chips off and send to other NAMers. I was very unhappy at the cost of removal, replacement and reprogramming from the local Dealer.

 

I have observe this with EOL semiconductor parts all the time. The inventory got scrapped out and sold by the pound to surplus buyers - to clean inventory, and the beancounters happy. The stock then got auctioned off or sold off to parties that think they can slowly sell them at elevated prices. A lot of these final retailers are in Asia.

The parts was original Motorola. Motorola spun off the semiconductor business that became Freescale so Motorola could focus in the lucrative business of building high margin smartphones. Today Motolora is no more except in the belly of Lenovo.

At about the same time, Phillips also decided that semiconductor business did not rack in gold as they wanted so it too spun off the lackluster semiconductor arm as NXP.

Fast forward NXP and Freescale decided to merge, which NXP ate Freescale. NXP EOL'ed this part is the last chapter as a 17 years old IC is not cost effective in any consumer product design.

 

Your experience pique my interest as I notice there is a thriving cottage industry on feeBay selling the MC33286DW ICs. Soon I gathered that it is a common cause of rear wiper failure on X5 and E39 (search on MC33286DW BMW). Wiper motor need a lot more current and I suspect it might be used to drive a relay would be my guess.

However searching on MC33286DW R53 mini your post is the only one that link the chip to failure though I didn't bother to read the other links except the excerpts. I was tempted to stock up a few but since there is no credible evidence it is a common Mini failure I decided to save my money.

Curiosity kills a cat. I would like to know what caused yours to fail.

 

Not sure what caused the failure: there was no apparent water damage.

The issue started out as a dead right brake light. With bulb changes not affecting repair my research guided me to any brake light issue and I found a number of people having to get their BC1 replaced. I'll go back and sift through the hundred posts or so and place links in my next message.

 

That was a lot easier than I thought. Plenty of posts if you Google "r53 brake bc1 replace"

https://www.northamericanmotoring.com/forums/stock-problems-issues/181887-questions-regarding-bc1-replacement.html#post2962130

https://www.northamericanmotoring.com/forums/stock-problems-issues/202391-body-control-module-replacement-questions.html

https://www.northamericanmotoring.com/forums/electrical/192439-time-to-replace-bcm-bc1.html

https://www.northamericanmotoring.com/forums/r50-r53-hatch-talk-2002-2006/214370-body-control-module-bc1-problems-need-help.html

https://www.northamericanmotoring.com/forums/electrical/265014-the-foot-well-module-functions-problems-solutions.html

https://www.northamericanmotoring.com/forums/stock-problems-issues/171227-body-control-module.html

And these are just from NAM Forum. There are other Forum's posts, too.