Brake Light Circuit sensor

More information needed. If it were a sensor or sensor wiring fault it would latch on in the normal way. If it goes on and off quickly more likely after the latching control unit.

Someone is FOS.

I'd guess this is an E36? (It helps a WHOLE BUNCH if we have some clue as to what BMW you're talking about... they've made several models in the 70 years they've been making cars..)

They're prone to doing this as the brake light switch under the dash starts to go bad. It has two parallel switches built into it. One that actually switches the brake lights and a second one that checks up on the first one (really.. I'm not making this up.)

Common failure, and a repeated failure. BMW has "improved" the switches, but some of the improved switches have also failed.

One other possibility is if you've replaced brake light bulbs with non-silver based bulbs (common brass based bulbs) - on some bulb monitoring systems this can add enough resistance to the circuit to trigger the brake-light warning. More common on the older E28 and E34 series and other BMW's of that era.

BRAKE LIGHT CIRCUIT error comes from the switch mounted to the brake pedal.

Remove the cover over your feet to gain access to the brake light switch. You can remove the entire switch via two screws. Your option is to disassemble the switch and clean the internals, or replace the switch. Quite frankly, cleaning the switch is a crap shoot, and you may find yourself reforming the contacts so that they close in the proper sequence reliably. There is more than one set of contacts inside the switch body, and they have to close in the correct order or the system detects some activity on the brake circuit, but no activity on the lighting circuit, and this lights the error message.

I repaired this message on my 4-door car a few weeks before it was wrecked, but I spent time figuring out what was happening inside the switch that I could have saved had I simply bought the switch in the first place.

Thanks for the information

Sorry. I should have identified the car more specifically. It's an E34 '95 525i.

104,000 miles, but the problem began occuring after factory bulbs began to fail Very possible that in replacing bulbs over the years I wound up with one that wasn't silver-based.

Jeff Strickland has had luck with cleaning the switch, but I may have an entirely different problem.

I have that same issue with my 2001 M3 as well as my previous 2001 330ci and before that, on my 1996 328is. The same issue with all of them. It seems to be a common problem but can't understand why the folks at BMW haven't solved this circuit fault by now. Has anyone has this issue with the E90?

Chris

On mine it was caused by the alternator. I had bulbs blowing quite often and frequently had BRAKE LIGHT CIRCUIT come up as I left the motorway and braked after a fast run. Any lights that were on would pulse and occasionally they would all go bright and the heater fan would get very loud. I replaced the voltage regulator (£40 from the dealer) on the alternator and never saw that message again. It also helped with engine hesitation and jerkiness and replacing the battery a few months later pretty much finished the job. It seems the electronics are quite sensitive.