BMW brake light circuit warning

brakes
bmw
lights
323

#1

The warning keeps on coming on even tho the brake lights work just fine. Mech says new tail light assemblies needed ($400-500 for a set of 2) and it’s a common problem for BMW, Mercedes, Volvos. Any helpful advice much welcome.


#2

Is it the warning that says a bulb is out? Have you tried replacing with exact same type bulbs the car came with? (all bulbs the same is the goal).


#3

Thanks. Nope, it’s not the bulbs, tho’ I had them replaced because my mech thought it might be caused by socket corrosion. The warning says “Brake light circuit - see owners manual.” It has a Priority One ranking, which means the warning stays on until the engine is off. If I restart the engine the warning goes away. The warning often stays off for weeks and then will reappear for no apparent reason. Btw, there is nothing in my owner’s manual about it.


#4

What year 323? And clearly all bulbs are working and we are not talking about a low brake pad warning, a handbrake on warning and not a low master cylinder fluid level warning?


#5

It’s a 1999 convertible w/ 69K mis. The “check control” warning comes on the dashboard and appearing on the control screen is the “Brake light circuit - check owner’s manual” notice. Again, the lights work fine when the warning appears. It might be that the circuit board in the tail light assembly just has a flaw from wear or it could be a reaction to extreme heat or cold (I’d guess about 1/2 of the incidences occur when the car has been exposed to very cold or very hot weather, which would indicate some reaction of the metal compound used in the circuit board.) I’m curious if this happens commonly in BMWs, Mercedes and Volvos as my trusted mech suggested.


#6

It is much more common in the earlier cars and the cause was using bulbs that had a slightly different current draw. Since 1999 is a switch year is your car a e-36 or e-46? I will call My BMW Master Tech friend and ask but he is at work now and not answering his phone (not at my beck and call)So keep looking at the post and I will try to get a more current techs view on the situation.


#7

I don’t know what e36 or 46 means, sorry. Thanks for the help - I appreciate it.


#8

It is the model designation. The cars look a lot alike. Two ways to find your model type. The hood struts (the little shocks that hold the hood up) will say e-36 or e-46 on them and the area at the bottom of the headlight housing on a e-36 is straight (parallel to the ground) and the same area on a e-46 has some curves in this area. Its a great way if you are looking at the car from the front to tell just which 3-series you are looking at.


#9

This might be helpful (from a BMW forum, specific to E46s):

http://www.bimmerfest.com/wiki/index.php?title=BMW_E46#Does_your_car_think_you_have_a_tail_light_out_when_you_have_no_burned_out_bulbs.3F


#10

Just checked. It’s an e-36 ZFK (from the hood strut).


#11

Master Tech friend says this is a high resistance brake light switch. The entire housing replacement fix does happen on all the cars of the year you speak of. The clue that it is the switch is that the message says “circuit”.

E-36 convertibles continued into production longer than the coupes or sedans,thats why you have such a late model e-36. Really hope this helps out.


#12

Oldschool,

Do you have any info on these lights in what kind of design they use. I assume there is some transistorized switching in them that adds to the cost of these lights. Is that correct?


#13

Thanks very much - your info confirms what my mech said too, i.e. that housing replacement is the answer. I appreciate the help.
All the best.


#14

I am not at all saying housing replacement is the problem,I am saying that the problem is with the brake light switch, but housings can be the source of the problem also. They can be visualy inspected to rule them in or out as the cause of the problem (inspect the bulb contact area) at times this area is too badly burned up to save them.

I don’t believe there is any type of switching going on in the housing but I will ask. I never had to replace any but I conclude it has become quite common.


#15

I see. I guess replacing the entire housing might just be the easiest solution for many mechanics. I did have several bulb contact assemblies replaced on the suspicion that corrosion was causing the warning to activate, but it had no effect. I read somewhere that there is a circuit switch under the brake pedal that is inexpensive but difficult to replace because it is hard to reach. Any value to that in your opinion?