What trips the brake warning light?

[Combatcm]

The other day on my way home the brake warning light was on....2000 non abs. I had to press the pedal all the way down for them to work.

I've owned it for 3 years and never did a brake job so i did the fronts. New pads rotors and bled them, fluid is full. Test drove it for a mile and everything was great. Then had to go to the parts store and came back everything was fine. The next time i went out the brake warning light was on again.

Any advice?

 

[BIGSLVRXJ]

The other day on my way home the brake warning light was on....2000 non abs. I had to press the pedal all the way down for them to work.

I've owned it for 3 years and never did a brake job so i did the fronts. New pads rotors and bled them, fluid is full. Test drove it for a mile and everything was great. Then had to go to the parts store and came back everything was fine. The next time i went out the brake warning light was on again.

Any advice?

Sounds like the start of a bad master cylinder to me. When they start going bad they'll loose pressure and you'll have to pump the pedal up to regain it.

 

[Rockslut]

The light will trip when it senses a difference in line pressure between the front and rear brakes. Like already mention, your master cylinder is on its way out.

 

[ehall]

There are two switches on that circuit. One is on the parking brake handle, so if it's raised any the light will come on. The other is on the valving block that is attached to the master cylinder, which will trip the light if there is a lack of hydraulic pressure. Easy test is to disconnect the wire from the valving block and see if the switch goes out, if so you have a problem with the brake hydraulics (MC, wheel cylinders, leak, ...) otherwise the parking brake handle is raised or shorted.

 

[themangeraaad]

I wouldn't jump straight to the master cylinder... check your rear brake lines for leaks. (can also crack open your brake fluid reservoir and check levels). If you find the rear brake fluid reservoir is low, well you got some hunting to do. I had my rear brake line rust out on me once and had this same symptom.

Does it feel like there is no (or very little) feedback all the way to the floor? Or is there some feedback and some stopping power but just VERY weak?

When my rear brake line went out I had zero stopping power until my pedal was almost on the floor, at which time the front brakes caught.

Just recently I installed a new rear axle and had the wheel cylinder bleeder valve snap off so I couldn't bleed the brakes. My brake light is on and I don't get much braking power until I am pretty close to the floor... but all through the throw of the pedal there is some braking power.

If you have zero braking before the floor then I would expect a leak. If there is some braking I would expect either a very small leak or that you somehow got air in the lines. Only way I can think to get air in the lines is to either have your fluid level extremely low (probably caused by a leak) or to have a brake bleeding issue like I did. Or just not bleeding them properly.

 

[RCP Phx]

Depending on how you bled the brakes will also trigger the "brakes" light.

 

[joe_peters]

Yeah, don't assume there is a problem. Some good advice posted above. Definitely inspect the rear brakes, lift the wheel cylinder rubber ends with a small screwdriver and check for wetness.

As said, the switch on the proportioning valve is triggered when there is a difference in the line's pressures. On the 80s Volvos we had to pull the switch and center the valve then reinstall the switch to turn off the light after servicing the brakes.