Brake Fluid Light Indicator

[realness]

Hi all,

I just recently purchased an 89 BMW 525i 150,000. I am currently having an issue with the Brake Fluid indicator light coming on and off. I checked the fluid and it was a little bit below the max line so I added some fluid to reach the line. When I first turn on the car the Brake Fluid indicator light is off. After driving for about 15 minutes it begins to come on and off. For example when I step on the gas the Brake Fluid indicator light goes off and as soon as I take my foot off the gas it comes on. Also when I step on the brake it goes off. When I take my foot off the brake it comes back on again.

Any idea to what is causing this and how can I fix it?

[realness]

Does anybody have any feedback on this?

Thanks

[uscharalph]

Does anybody have any feedback on this?

Thanks

I have no experience on the matter. My guess would be the brake fluid level sensor.

[DanDombrowski]

The brake booster operates on the vacuum on the intake manifold. When you step on the gas, the pressure in the intake manifold increases, when at idle, the throttle plate is closed and there is very little pressure. I'm not really sure, but this may cause the plunger in the master cylinder to move by small amounts, causing the fluid level to raise and lower by a small amount. Mabye you have a leak, and after 15 minutes it leaks just to the edge of the sensor? If the resivoir is full and it keeps going on and off, it may be the sensor.

[realness]

The reservoir is still full and it continues to go on and off as I described in my first post. It is up to the max line. I filled it up this past Saturday when the problem began. Even then it wasn’t really that low, but I filled it up any way to the max line thinking that would cure the problem. It apparently didn’t work.

If it is the sensor. How do I fix that? Is the sensor the wire that connects to the top of the reservoir cap?

I greatly appreciate both of your replies.
Thanks

[632 Regal]

What did you do before this started?

The reservoir is still full and it continues to go on and off as I described in my first post. It is up to the max line. I filled it up this past Saturday when the problem began. Even then it wasn’t really that low, but I filled it up any way to the max line thinking that would cure the problem. It apparently didn’t work.

If it is the sensor. How do I fix that? Is the sensor the wire that connects to the top of the reservoir cap?

I greatly appreciate both of your replies.
Thanks

[pyro]

Allright theres a little plastic "cup" inside the brake fluid resivor and it has a TINY hole in the bottom to let fluid in and out of it as the levil goes up and down. What that cup does is keeps the fluid around the sensor at the same level during acceleration and brakeing. As when you accelerate and decelerate the fluid can slosh back and forth that "cup " prevents it from sloshing.

Picture is of cup half way removed... check if you have that

[realness]

What did you do before this started?

I did not do anything. It just started to happen all of a sudden.

[realness]

Allright theres a little plastic "cup" inside the brake fluid resivor and it has a TINY hole in the bottom to let fluid in and out of it as the levil goes up and down. What that cup does is keeps the fluid around the sensor at the same level during acceleration and brakeing. As when you accelerate and decelerate the fluid can slosh back and forth that "cup " prevents it from sloshing.

Picture is of cup half way removed... check if you have that

Yes I do have that "cup" inside the brake fluid reservoir.

[realness]

Hi all,

I am still having this problem with the brake fluid indicator coming on. I also noticed that when the brake fluid light indictor comes on the rpm needle start acting up. It just starts going up and down erratically when I have my foot on gas. Or sometimes when I have my foot on the gas the rpm needle will just stay put at the bottom 0. I also noticed that when I turn the heat on while driving everything become normal. The brake fluid indicator light turns off and the rpm needle works properly. Also The brake fluid is still full.

Does anyone have any advice?