Brake Light Circuit sensor

There is much good advice to be had here from a group
of knowledgable posters, so I'm going to see if there's any
remedy for an annoying liitle problem.

Brake Light Circuit sensor (idiot light) comes on at random times,
even though all brake lights are working properly. This is not
related to the wear sensor lights, which have appeared for the front
and rear and were promptly replaced with the pads, etc.

Someone said that the circuit needs to see a specific load when
braking and any variance will cause the warning light to appear.
Why would the load change?

In article >,
> wrote:
> There is much good advice to be had here from a group
> of knowledgable posters, so I'm going to see if there's any
> remedy for an annoying liitle problem.

> Brake Light Circuit sensor (idiot light) comes on at random times,
> even though all brake lights are working properly. This is not
> related to the wear sensor lights, which have appeared for the front
> and rear and were promptly replaced with the pads, etc.

> Someone said that the circuit needs to see a specific load when
> braking and any variance will cause the warning light to appear.
> Why would the load change?

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.

--
*A hangover is the wrath of grapes.

Dave Plowman London SW
To e-mail, change noise into sound.

wrote:
> There is much good advice to be had here from a group
> of knowledgable posters, so I'm going to see if there's any
> remedy for an annoying liitle problem.
>
> Brake Light Circuit sensor (idiot light) comes on at random times,
> even though all brake lights are working properly. This is not
> related to the wear sensor lights, which have appeared for the front
> and rear and were promptly replaced with the pads, etc.
>
> Someone said that the circuit needs to see a specific load when
> braking and any variance will cause the warning light to appear.
> Why would the load change?

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.







> wrote in message
...
> There is much good advice to be had here from a group
> of knowledgable posters, so I'm going to see if there's any
> remedy for an annoying liitle problem.
>
> Brake Light Circuit sensor (idiot light) comes on at random times,
> even though all brake lights are working properly. This is not
> related to the wear sensor lights, which have appeared for the front
> and rear and were promptly replaced with the pads, etc.
>
> Someone said that the circuit needs to see a specific load when
> braking and any variance will cause the warning light to appear.
> Why would the load change?

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.



> wrote:
> > There is much good advice to be had here from a group
> > of knowledgable posters, so I'm going to see if there's any
> > remedy for an annoying liitle problem.
> >
> > Brake Light Circuit sensor (idiot light) comes on at random times,
> > even though all brake lights are working properly. This is not
> > related to the wear sensor lights, which have appeared for the front
> > and rear and were promptly replaced with the pads, etc.
> >
> > Someone said that the circuit needs to see a specific load when
> > braking and any variance will cause the warning light to appear.
> > Why would the load change?
>
> 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.
>

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


"admin" > wrote in message
...
> wrote:
>> There is much good advice to be had here from a group
>> of knowledgable posters, so I'm going to see if there's any remedy for an
>> annoying liitle problem.
>>
>> Brake Light Circuit sensor (idiot light) comes on at random times,
>> even though all brake lights are working properly. This is not related to
>> the wear sensor lights, which have appeared for the front
>> and rear and were promptly replaced with the pads, etc.
>>
>> Someone said that the circuit needs to see a specific load when
>> braking and any variance will cause the warning light to appear.
>> Why would the load change?
>
> 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.

> wrote in message
...
> 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.

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.