Dreaded brake circuit demon

[98_328i]

Hey everyone, I've been lurking on here for the past month or so. The typical brake circuit failure got me to register today though. I picked up a really clean 98 328i that was traded in at work a few weeks ago. It had a few small issues but nothing major. However, the intermittent brake circuit failure is giving me a headache though. I pulled the taillight inspection covers off and started pulling bulbs out. Two of the brake light bulbs had the typical burn spots in them so I replaced them. Upon closer inspection of the old bulbs they had a buildup on the filament that I've never seen happen before (been in the automotive business for 6 years now). I replaced the bulbs and everything was good for a few days. About 4 days later the light popped back on again. I drove the car for another week and the light only came on once or twice.

Fast forward to last night. I was driving home on the highway and I came into a reduced speed zone so I went to disengage the cruise control on the switch. As soon as I disengaged it on the switch the circuit failure message popped up. On the way into work the message came on almost immediately.

Does this sound like a corrosion problem or does it sound like I need a brake light switch?


Also, I went to pull another bulb socket out and I actually had to grab a pair of pliers to get it to break loose from the tail light housing. That bulb wound up being fine but I was curious if this was a tell tale sign for anything else.

[chaz58]

Well, if you search, you can find LOTS of info on this.

If all 3 of your brake lights go out at once, then it is the switch (under the brake pedal). If it is just one (or two) lights, then it is a problem with the connection in the lens.

I spent a couple of months trying to figure this one out, but in the end I just put electrical tape over the light on the dash. If you have burn marks on the contacts, that is a good indication of where the problem is coming from.

You can try this:

clean the contacts
change the bulbs
bend the contacts back out for better pressure
put die-electric grease on the contacts.



Someone once said that BMW bulbs have a different resistance, and wont' trigger the warning message so easily. I don't have any experience to know if that is true or not.

[ronpapworth]

I find my brake switch trips the sensor whenever the foot well is warm. It did it for most of summer and only does it when I have heat blowing on my feet. It's probably the switch but also could be the bulb holders. I think I saw a write up once that if there is corrosion on the contacts it will continue to trip. You probably know that there are two different switches down there as well...

[98_328i]

Okay, just to help clarify some things: what are the differences in between a brake switch being bad and having bad connections?

[ColumbusBMW]

If you have cleaned and realigned the bulb connections and the 'brake light failure' continues to com on and the brake lights are still working, then it almost has to be the switch. I had this problem and everything was the way it should be at the bulb connections. I bent the prongs out, changed bulbs and added the dielectric grease. I had installed aftermarket smoked lenses and changed back to original and still had the problem. It ended up being the switch. I replaced the switch and I have never had the problem again. Took me about 4 months to figure out all of this. Then it took me $25 and about 15 minutes to fix it. Good Luck!

[TheOnlyE36]

Well, if you search, you can find LOTS of info on this.

If all 3 of your brake lights go out at once, then it is the switch (under the brake pedal). If it is just one (or two) lights, then it is a problem with the connection in the lens.

I spent a couple of months trying to figure this one out, but in the end I just put electrical tape over the light on the dash. If you have burn marks on the contacts, that is a good indication of where the problem is coming from.

You can try this:

clean the contacts
change the bulbs
bend the contacts back out for better pressure
put die-electric grease on the contacts.



Someone once said that BMW bulbs have a different resistance, and wont' trigger the warning message so easily. I don't have any experience to know if that is true or not.

:thumbup: