Check Brake Light Circuit

The message "Check Brake Light Circuit" has been popping up on my 1997 M3. It happens sporadically. Upon visual inspection, there seems to be
nothing wrong: The brake lights behave correctly, no fuses are burned. The message sometimes goes away when the ignition is turned off and back on. Sometimes it persists.
I'd like to say that this is seasonal - I've seen it happens more often when it is cold. But I can't confirm it. It seems to happen whenever the hell it feels like it. I live in Florida, so this may not mean much anyway.
I took it to the dealer, of course the message refused to show then. Mechanic grumbled something about brake pedal sensor, and $500 to diagnose (!).
Anyone encounter this problem, and any advice?
Thanks!
t o n y
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There is a switch that costs aobut $10 that causes this message. There is no troubleshooting involved, and the failing switch is well known. It takes a few minutes to get the cover off from over the pedals, then another few minutes to get the switch off and the new one on.
With the uncomfortable contortions that it takes to work around the pedals, it should take less than 1/2 hour to replace.

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Yes, brake light switch. It is actually two switches in one. One operates the lights and the other is a diagnostic input to the LKM.
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LKM?
--
*The sooner you fall behind, the more time you'll have to catch up *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Like the others said it's the brake light switch behind the pedal. There are two different switches that could be there, a 2-pin (pn 61 31 8 360 420) or a 4-pin (pn 61 31 1 382 385). Check to see what you have before buying the wrong one. Both can be had for $10-20 each.
https://www.autohausaz.com/catalog/lookup_parts.cfm?SubcategoryIDG20&VehicleID 13252&CFIDa1151&CFToken282279
http://www.bavauto.com/shop.asp
$500 to diagnose this problem? Where did you take your car? I've been to Reeve's in Tampa and All Pro in Ocala for electrical problems that I couldn't do myself. Both are much more reasonable than that.
Kyle. 97 M3 98 740iL
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Kyle and Lori Greene wrote:

https://www.autohausaz.com/catalog/lookup_parts.cfm?SubcategoryIDG20&VehicleID 13252&CFIDa1151&CFToken282279
Thanks - very useful. The estimate was from the mechanic rep, at a BMW dealer in Jacksonville.
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