Brake Light Circuit Error Message

[BlackOnBlack]

Yesterday I got a "Brake Lt Circuit" warning message. I checked the Brake Lights and all three work. No warning this morning and today while driving a total of about 55 miles until I got home, pulling into the driveway, it came on again. Checked again and all three lights were working.
It rained quite a bit yesterday, but I don't believe I have any leaks.

Any ideas?

[Paul in NZ]

brake light switch itself.....

[granit_silber]

Yesterday I got a "Brake Lt Circuit" warning message. I checked the Brake Lights and all three work. No warning this morning and today while driving a total of about 55 miles until I got home, pulling into the driveway, it came on again. Checked again and all three lights were working.
It rained quite a bit yesterday, but I don't believe I have any leaks.

Any ideas?

I had the same thing happen to my 525. After checking all the possible culprits, was told that the Brake Lt Circuit warning sometimes just happens on these cars; an electrical gremlin.

-ashley

[Qsilver7]

this is a well documented failure that is usually repaired when you fix or replace your brake light switch (behind the brake pedal).

Don Gale has a great write-up on his web site on how to replace the brake light switch: http://www.nmia.com/~dgnrg/page_25.htm

Here's the diagram of the switch's location from the online parts database...see item #24 (for 5 spd tranny): http://www.realoem.com/bmw/showparts.do?model=HD53&mospid=47404&prod=19920300&btnr=35_0057&hg=35&fg=05&hl=159

[Brett619310]

I had the same thing happen to my 525. After checking all the possible culprits, was told that the Brake Lt Circuit warning sometimes just happens on these cars; an electrical gremlin.

-ashley
I have actually had this problem on every BMW I have ever owned... its not just specific to the E34. It has always been fixed by replacing the switch behind the pedal... about a $20 DIY job. You think they would have fixed the problem by now.

[pmulry]

I wonder if the real problem isn't somewhere in the programming and changing out the brake switch just eliminates one fault that could trigger the bad program.

Why do I say that? I was getting the same message for awhile, and then I got the brake linings message. Pads on the back wheels were skinny, but the fronts weren't much better, so I did all 4 wheels and replaced the sensors while I was at it, and bled the system. Next startup after the work, no brake linings message, no brake circuit message. It was fairly warm the other day after being colder, too, which is sometimes tabbed as a culprit symptom with this problem.

Also, the fact that BMW hasn't gotten this fixed indicates (to me) that this is more a software problem than a hardware problem. Which means that we'll never rid ourselves of it. Oh well.

[Javier]

in the LKM brake lights monitor. I have this message every time I got into a traffic jam, keeping brake lights on for long time.

This makes me believe the sensing resistor gets hot, rises its value and false sense and onevercurrent in the circuit.

Yes I did cahnge the brake lights switch already, nothing changed. It may be the culprit for some cases, but not all of them.

If you have a handy donor, try switching LKM's and see if fault disapears.

Javier

[Qsilver7]

we just did this for a friends 91 735iL...he was experiencing the headlights going out randomly...so we pulled the LKM and resoldered the relay joints. But also resoldered some other points after looking through a magnifying glass and saw that there were some more cracks.

I spoke with his girlfriend the other day to ask how was the fix holding up...and she stated that the headlights were working great and that he no longer has the "brake lt circuit" warning anymore.

So even though my first response was to change the brake light switch...maybe taking a close look at the LKM might do the trick if the problem persists. The smaller crack was about an inch to the right of the relays on the left side of the board (when you have the board open and in front of you).

FYI :)