Brake light warning light

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sideshowbob
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Brake light warning light

Post by sideshowbob »

My 1988 635 CSi is now on a SORN and under a dust cover in my garage. run her up to temperature and check all lights, windows, computer, sunroof etc. are working.

I have just gone through one of these checks and discovered a fault !!

On the instrument panel the Check control light will not go out even after depressing the brake pedal. On checking the check panel the warning light is on for 'Brake Lights'.

I have checked the rear of the car and BOTH brake lights are inoperative. Have checked the bulbs, they are Ok. Have checked fuse 6 again OK. Checked and topped up brake resevoir with fluid OK.

Hoewever the fault and warning light is still on. Am I righjt in thinking there is a switch on the brake pedal mechanism that controls the on/off operation of the lights, as it seems both are inoperative. If it is this switch, how easy is it to get to and repair/replace.

Any comments would be appreciated
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Post by ron »

Maybe it's just a wire come adrift. The switch is above the arm of the pedal.
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Post by Chris Wright »

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JCS
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Brake fluid reservoir switch in cap

Post by JCS »

It could be the brake reservoir low level switch built into the reservoir cap.
Happened on mine.
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Re: Brake fluid reservoir switch in cap

Post by Chris Wright »

JCS wrote:It could be the brake reservoir low level switch built into the reservoir cap.
Happened on mine.
Check the ETM, that is one of three switches that activate the Brake Warning light in the cluster.
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World-Class6
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Post by World-Class6 »

Chris Wright wrote:Replacing the brake light switch:
http://www.malloc.nl/BMW/635CSi/pages/e ... l#refertoc

Adjusting the switch:
http://www.malloc.nl/BMW/635CSi/pages/e ... l#refertoc
thanks for that~ it feels like at times brake light switches are annoying and go out routinely. Uhm, perhaps it's my lead foot breaking them :mrgreen: I recently replaced brake light switch on 95 MBZ and have just ordered a brake light switch for 95 RRC and now ///M anny needs one as well. :roll:
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Post by tschultz »

Check for electrical connections and for electrical corrosion on the bulbs/ housings.

Brake light switch is another good idea.
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sideshowbob
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Re: Brake fluid reservoir switch in cap

Post by sideshowbob »

Chris Wright wrote:
JCS wrote:It could be the brake reservoir low level switch built into the reservoir cap.
Happened on mine.
Check the ETM, that is one of three switches that activate the Brake Warning light in the cluster.
Sorry to sound a bit dense but what is the ETM and what and where are the three switches sitiuated that activate the Brake Warning light in the cluster.
My problem is that the actual brake lights are not working at all and the warning light is on, telling me that I have this fault. So other than the brake switch on the pedal and a broken wire or fuse common to both rear brake lights what else can cause BOTH lights to stop working at once.
Something and I don't know what it can be but it must be common to both lights has caused this failure...my first thought is therefore the brake light switch fitted to the pedal.
Any other ideas

Thanks
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Re: Brake fluid reservoir switch in cap

Post by ron »

sideshowbob wrote: Sorry to sound a bit dense but what is the ETM and what and where are the three switches sitiuated that activate the Brake Warning light in the cluster.
ETM is the Electrical Troubleshooting Manual. There are 2 switches on the pressure regulator and the 3rd. on the brake M/C.

http://bmwfans.info/parts/catalog/E24/C ... cumulator/
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sideshowbob
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Post by sideshowbob »

Thanks for that, however ,I can understand how a brake pressure sensor failure would cause the check warning light to come on, but would it stop the brake lights from functioning ?

I have noticed in the ETM that it refers to a Rear Light Check relay. This appears to be made up of a series of contacts and coils that are linked to various rear light circuits and functions. If this were faulty on the brake light circuit would it stop the rear brake lights from functioning and cause the check light to operate ?

Has anyone any experiences good or bad of this check relay and where exactly is it situated and is it repairable ?
Chris Wright

Post by Chris Wright »

sideshowbob wrote:Thanks for that, however, I can understand how a brake pressure sensor failure would cause the check warning light to come on, but would it stop the brake lights from functioning ?
No, there is no connection between the two and a brake pressure sensor failure would not cause the check warning light in the Active Check Pnel to come on
___

I'm sorry, I wasn't clear. I was saying it couldn't be the Brake Reservoir Low Level switch built into the reservoir cap that is causing the problem because it lights the Brake Warning light in the cluster, which is different than the Bake Stop Light waring that you are taking about in the Active Check Panel (Annunciator) to the left of the cluster. The Brake Warning light in the cluster comes on when the brake fluid is low, the brake booster system is below approx. 320psi or the power steering pump output goes below 22psi (Page 6210-2 of the '89 ETM). It has noting to do with the Stop light warning in the Active Check panel.
___

Have you checked the Stop Light switch at the brake pedal yet?

Are all three of the brake lights inoperative (the third one in the back window also)?

If all three are out, check the brake switch with a meter** and if it tests good, adjust it or, if not, then replace it (see the links above).

In the unlikely event that the third brake light in the rear window works, you need to check the active Check Panel Relay in the trunk. Let us know.

** With the key on, one wire to the brake light switch will have voltage and the other will only see voltage when you press in the plunger with your finger.
sideshowbob
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Post by sideshowbob »

Sorry that it has taken so long to get back with a reply, but the car has been laid up in my garage well away from the British winter. Finally got her out last weekend and checked the brake warning switch gave it a few wiggles and applied a bit of lubricant and ...hey presto ! brake lights working and check control panel behaving itself.
Thanks everyone for all your advice, now have the tricky job of replacing the lower dashboard panel !!
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Post by songzunhuang »

sideshowbob wrote:Sorry that it has taken so long to get back with a reply, but the car has been laid up in my garage well away from the British winter. Finally got her out last weekend and checked the brake warning switch gave it a few wiggles and applied a bit of lubricant and ...hey presto ! brake lights working and check control panel behaving itself.
Thanks everyone for all your advice, now have the tricky job of replacing the lower dashboard panel !!
This thread is very old, but the problem popped up for me. I was getting the Brake Light warning in the active panel every once in a while (left of steering wheel for USA model) and then one day it stayed on.

Looking at my brake lights, they are both out. I changed the bulbs but they are still out. So I took out the switch at the brake pedal and tested it with my multimeter and it checks out fine. This is becoming a head scratcher.

One odd thing is that my in my fusebox, there is no fuse #6. It's simply empty. Is there supposed to be a fuse there? My brake lights used to work before and there has never been a fuse in that slot as far as i know. So how the heck did they work before if fuse #6 is needed?

Anyway, this is added to my long list of projects on the car this weekend. Any Insight would be great, thanks.
-----
Song Huang
1984 633CSi
Last 7 of VIN: 6997383
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Back in action

Post by songzunhuang »

I just wanted to follow up. I cleaned up my brake light switch and tested it with a multimeter and it was ok. So I re-installed it. Then I decided to put a fuse in #6.

Well guess what? It's working again. However it's still kinda weird because when I am driving and I brake, the light in the dash will come on every once in a while. The light to the left of the steering wheel stays out now.

I'll have to poke around and try to understand this better...
-----
Song Huang
1984 633CSi
Last 7 of VIN: 6997383
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sansouci
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Post by sansouci »

Do you have a vacuum or hydraulic booster? The hydraulic accumulator (da "bomb") will fail to retain its nitrogen charge and give a hard pedal and a flash on the brake indicator.
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Post by songzunhuang »

sansouci wrote:Do you have a vacuum or hydraulic booster? The hydraulic accumulator (da "bomb") will fail to retain its nitrogen charge and give a hard pedal and a flash on the brake indicator.
I don't even know how to begin to answer your question! Sorry for the newbie question, but how can I tell? I have a 1984 633CSi.
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Song Huang
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sansouci
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Post by sansouci »

Song,
you likely have a master cylinder with a plastic reservoir. Behind it on the firewall is the brake booster. Outboard of that is the pressure regulator. Hanging down and not readily visible is a black painted sphere. Da bomb.
As I have suggested, go to realoem with your last 7 digits and look around. In this case, the brake system diagrams will be helpful.
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Perhaps I have a vacuum assist?

Post by songzunhuang »

sansouci wrote:Do you have a vacuum or hydraulic booster? The hydraulic accumulator (da "bomb") will fail to retain its nitrogen charge and give a hard pedal and a flash on the brake indicator.
So my attention turns back to this since I get momentary flashes of "Brake" on the instrument cluster. I have not been able to find anything that looks like "Da Bomb" at this time. I'll crawl around some more later.

I filled the ATF reservoir using the 20 pump method I have read about in the forum, but still the light comes one momentarily. It only comes on when I first tap the brakes, if that makes any difference. Also, it doesn't come on every time I tap the pedal, only on occasion.

Ideas?
-----
Song Huang
1984 633CSi
Last 7 of VIN: 6997383
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Post by m6dave »

Song
Based on the vin in your signature realoem says you have hydraulic assist. Item 4 is da bomb.
http://www.realoem.com/bmw/enUS/showpar ... Id=34_0274

This should be located to the rear of the left hand strut tower under the hydraulic pressure regulator block. (incorrectly called voltage regulator in the link above)
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Post by songzunhuang »

m6dave wrote:Song
Based on the vin in your signature realoem says you have hydraulic assist. Item 4 is da bomb.
http://www.realoem.com/bmw/enUS/showpar ... Id=34_0274

This should be located to the rear of the left hand strut tower under the hydraulic pressure regulator block. (incorrectly called voltage regulator in the link above)
I must be looking in the wrong place. That "Bomb" is a pretty distinctive part and I can't see how I would miss it! To see it, you look from the engine compartment right? That's where I was looking - crawling about from many angles.

OK, this will have to be reserved for next weekend as it's Monday and work beckons...
-----
Song Huang
1984 633CSi
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Re: Brake light warning light

Post by maestro84 »

I have a tail light warning on the control panel. The lights are working when i apply the brakes. The brake light switch is new as well as the bulbs. The control box in the trunk was rusty but overhauled by a specialist and he confirmed its working. I tried a different control box (from a younger 635, the writings were different but otherwise the unit looked the same) but the warning light didnt go out.
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Re: Brake light warning light

Post by Brucey »

if you can check the current drawn by each bulb you may find that they are not all the same. The bulbs can come 'on' without drawing their full whack of current if the connections are a bit grubby or if the bulb ratings are lower than they should be (eg if there are LED bulbs fitted....).

Also note that the check panel light always comes on and stays on until you apply the brakes for the first time.

To keep the check panel light from staying on all the time with LED bulbs fitted, you can install a resistor in parallel with the bulbs. If you get the resistor rating wrong, actual bulb failure may no longer be indicated reliably.

cheers
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Re: Brake light warning light

Post by maestro84 »

Brucey wrote: Tue Jul 17, 2018 1:30 pm if you can check the current drawn by each bulb you may find that they are not all the same. The bulbs can come 'on' without drawing their full whack of current if the connections are a bit grubby or if the bulb ratings are lower than they should be (eg if there are LED bulbs fitted....).

Also note that the check panel light always comes on and stays on until you apply the brakes for the first time.

To keep the check panel light from staying on all the time with LED bulbs fitted, you can install a resistor in parallel with the bulbs. If you get the resistor rating wrong, actual bulb failure may no longer be indicated reliably.

cheers
Thanks for the reply. Only the tail light warning comes on the check panel and stays even if i press the brake. No led bulbs. Both tail light bulbs are new Hella 12v 21w. I will check connections but i believe it wont be the problem.
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Re: Brake light warning light

Post by Brucey »

sorry I didn't read what you wrote carefully enough, tails lights.... it is only the brake light check panel that comes on and goes off as I describe.

I have had episodes of tail light warning and it has always turned out that there is a duff bulb or an intermittent duff connection in the light housing of some kind.

Mad thought; the tail lights are often (deliberately or accidentally) wired differently between US and Euro spec cars; is the check panel control unit either

a) specific to the model of car or

b) reading the correct bulb ratings?

From memory 21W sounds like a brake light bulb rating, not a tail light rating...?

cheers
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Re: Brake light warning light

Post by maestro84 »

Brucey wrote: Tue Jul 17, 2018 2:31 pm sorry I didn't read what you wrote carefully enough, tails lights.... it is only the brake light check panel that comes on and goes off as I describe.

I have had episodes of tail light warning and it has always turned out that there is a duff bulb or an intermittent duff connection in the light housing of some kind.

Mad thought; the tail lights are often (deliberately or accidentally) wired differently between US and Euro spec cars; is the check panel control unit either

a) specific to the model of car or

b) reading the correct bulb ratings?

From memory 21W sounds like a brake light bulb rating, not a tail light rating...?

cheers
Sorry my mistake. Its the brake light (Bremslicht) warning with the sign of (!) on the check panel (top left). No other warning lights on.
The check panel is euro spec as the car.
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