Brake Light Circuit...

[starship1701a]

this morning for the first time, i saw this new message on the computer screen, "Brake Light Circuit + see owners manual"... not sure what to make of this? brake lamps work fine...

footnote, i do have some broken wires inside the trunk where the cables come in, from the constant opening and closing... i realize i have to take it apart and resolder some wire extensions... one tail lamp is out as a result of this... could this be related to my current problem?

Or has anybody experienced this before?

[53helofe]

Could be, did you notice the broken wire or that the tail lamp was out before seeing this message?

I get the lic plate fail message on mine from time to time after it sits for a week or two but always goes out after the second start.

[legoman67]

this is a very common problem in the E34's. Usually its the trunk wiring(at the hinge), the brake light switch behind the pedal, or one of the tail light housings. Generally if you see this warning you will not have any brake lights. so drive carefully.


Also, i heard recently that BMW has an active recall for this problem(in the e34 chassis at least). I found that kinda of surprising, but it might be worth checking out..

[tvjake2]

I get this warning occasionally. It shows up and then mysteriously goes away. I'm betting it's wiring issues.

[starship1701a]

My brakes lights all work ... Checked the fuses they look good too...

[EEDegreeToDrive]

Brake switch.. Had this problem on my E31 and E32. It's about $20.

Interesting is that it has some built in redundancy, so will sometimes continue to work (thats why you get the error, it sees the lack of redundanry I believe).

[Timm]

Yes, the brake light switch (under the pedal) has two contacts that switch in reverse (one opens while the other one closes and vice versa) - the redundancy is for the cruise control. If the two switch elements show incompatible states you will get the 'Brake Circuit' (rather than brake light when a bulb fails) warning. This will inhibit the cruise control system if the warning is shown.

[mjrgroup]

I too would suspect the brake light switch at the pedal as that is a wear component and prone to failure...however, on the brake and power steering regulator there is a switch with electrical connections....this is a shot in the dark, but could that ever trigger a brake circuit warning?



#5 Oil Pressure Switch 34351182270

[legoman67]

That switch would trigger the master brake warning light which means the brake functionality is at risk. The circuit error is just an electrical error regarding the brake lights, it has no relation to the mechanical workings of the brakes.

I too would suspect the brake light switch at the pedal as that is a wear component and prone to failure...however, on the brake and power steering regulator there is a switch with electrical connections....this is a shot in the dark, but could that ever trigger a brake circuit warning?



#5 Oil Pressure Switch 34351182270

[mjrgroup]

I understand now, thanks for the clarification.

[starship1701a]

the error messages has ceased... recently i had my Heater core replaced and i think the wiring may have come loose during this process... i will be preparing to cramp up my back and look up under the dash this weekend to verify...

thanks to all for the enlightening information about this little brake light switch devil... gotta fix all those broken boot lid wires too...

[EEDegreeToDrive]

the error messages has ceased... recently i had my Heater core replaced and i think the wiring may have come loose during this process... i will be preparing to cramp up my back and look up under the dash this weekend to verify...

thanks to all for the enlightening information about this little brake light switch devil... gotta fix all those broken boot lid wires too...

Unless you replaced the switch, the error will come back some day.

Worse, is that if the other pair of contacts quit, you'll have no brake lights (and possibly no warning).

[legoman67]

i just replaced the switch in my e34 the other day after talking about it in this thread. Not very hard once you figure out how it un-clips from the pedal box... no wonder you see so many of them zip tied in.

[ChrisFuture8]

I intermittently also get the error on the MID. Mine turned out to be a loose light bulb on the driver's side. I suspected the heavy trunk may contributed to the cause in my case as it's pretty heavy and over time can cause bulbs to come loose.

[Timm]

I intermittently also get the error on the MID. Mine turned out to be a loose light bulb on the driver's side. I suspected the heavy trunk may contributed to the cause in my case as it's pretty heavy and over time can cause bulbs to come loose.

Don't confuse Brake Light Failure (which is common when a bulb fails or the boot-hinge loom fails) with Brake Light Circuit Failure (which points to a under-pedal switch failure).

[Tomcat BMW]

Does anyone have a part # and good source for this item in a 1991 850i?
brake light switch on brake pedal