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Discussion Starter · #1 ·
I have a '97 328i that is doing some strange stuff on the brake circuit. I was getting an intermittent "Brake Circuit Failure" message once every few days but it never amounted to much; just shut it off and turn back on, and away it went. I replaced my 4-wire brake switch and thought that would be the end of it.

Well it showed up again sporadically. Then one day it came on again and I thought nothing of it as usual. I happened to have my cruise control engaged around 50mph and approached a red light. Well surprise surprise, the cruise didn't disengage when I pressed the brakes! Took me a second to comprehend what was happening; not a nice sensation.

In any case, the "Brake Circuit Failure" message now comes on every time I use the brake after start-up, and the cruise will never disengage (unless I manually turn it off). Further, ALL brake lights are now non-functional!

The fuse is good, and I have power at both circuits of the brake switch (4-wire switch). The switch is new and appears to be working fine; a multimeter shows continuity on both circuits when the pedal is pressed, as expected. The connector contacts look fine but I cleaned them just in case.

The switch or connector would seem to be the culprit, but both appear fine. Ideas anyone??? I see an X181 connection point in the wiring diagram that I'm wondering about, but this just doesn't feel right.
 

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Discussion Starter · #3 ·
A-ha!

It turns out the connector WAS the culprit! It was the connection between the wire harness and the brake light switch. Everything looked good visually, and the components checked out electrically. Even though the connector had snapped into place, there was still a little travel left in the connection. Pushing together with more force made up the circuit. All better!
 

· BuckFifty
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342 Posts
In addition to your problem, it is very common the brake lights will register a fail due to bad contact between the bulb and socket. I had to clean both sides with a polishing bit on my dremel to fix it. After fixing it the first time, I think the higher current flowing through burned out the bulb very quickly and I had to change that afterwards.
 
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