Brake light coming on in cold weather?

pr5pixie

Member
I've noticed recently that my brake light has started coming on in cooler weather when I brake. Sometimes it only flicks on when I'm braking, sometimes it stays on while idling and then goes off when I start moving again, and sometimes it just stays on the entire time i'm driving after I brake initially. it doesnt seem to matter whether the motor is warm or not, but what the weather is like outside. I have a 2003 P5 with about 14k on it and have never had work done. And yes, I know the e-brake it not on :)
I'm getting mixed reactions from people-- some say it cant be the fluid cause the light isnt hooked up to it, some say it cant/can be the pads (there is no squeeling at all) some say the light is just sticking, but then why would it come on only while braking?
I dont know much about P5s (I owned a geo before and did most of my own work) but I'd hate to bring it in if its just low on fluid. However, I dont even know HOW to check the fluid in this car, and it IS under warentee so I dont want to screw with it....
Any advice? I tried a search and got nothin...
 
once more, another damn thread. it's the brake fluid, due to the cold weather the fluid contracts. So when the car is cold, not warmed up, fill it up. There are 1000000 threads flyin around. SEARCH people.
 
yep, check the fluid as it's a common reason for the light to flicker and exhibit that behavior
 
^^I ran a search under "brake light" and didn't see anything related. I do appreciate the info, though.

I spose I need to go buy a hayes manual and figure out how to fix this eh?
 
no manual needed. Go buy DOT-3 brake fluid and when the car is cold fill the brake reservoir. It's the thing in the drivers side against the firewall
 
There is no fix. If you're low on fluid,put in some more. If you are not, then just get new pads, they are low.

Last winter I drove for 3 months with the brake light coming on every day and only going away sometimes during my commute. Fluid was fine. Changed pads and the light went away
 
weird that the light went away when you put new pads on since the car has no idea how much pad is left.... thats why when you ARE Low on the pads, you get a nice metaly noise to indicate they are on their last leg.
 
^^yeah thats what I thought too...I didnt think there were sensors that could indicate the thickness of the pads, I figured the only way to tell was from the sound...?
 
pdhaudio83 said:
weird that the light went away when you put new pads on since the car has no idea how much pad is left.... thats why when you ARE Low on the pads, you get a nice metaly noise to indicate they are on their last leg.
I don't remember hearing the noise, but who knows, maybe it was just because of loud music?

When the pads are low it takes more fluid to push them against the rotor, so the fluid taken from the reservoir is increased, making the sensor see low fluid, which triggers the brake light.
Add that to the whole cold weather and fluid contracting and needing to warm up and you have a car that doesn't have too low brakes, but that with the winter weather causes the light to be on 24/7.
 
So, for someone who has never done ANY kind of brake work, its going to be easy to find/fill the reservoir?
also, how does the fluid get low other than having lowish pads? I was under the impression that it couldnt get low any way aside from the master cylinder leaking, but again, i'm used to a 93 geo so i could be wrong ;)
 
yep. its mounted to the back of the firewall near the air intake pipe that connects to the throttle body.
 
pr5pixie said:
So, for someone who has never done ANY kind of brake work, its going to be easy to find/fill the reservoir?


It's right in the engine bay against the firewall on the driver's side.
 
on the attached immage, it is the reservoir that is circled. Just remove the cap and fill with the recomended DOT-3 fluid until it reaches a little above the full mark on the side. But do it when the car is cold
 

Attachments

  • brak helper.JPG
    brak helper.JPG
    133.1 KB · Views: 245
Back