My instrument panel brake light stays on when the car is running.
1. Front and rear brakes have been inspected and cleaned. Plenty of material on both the front pads and rear drum brake shoes. No fluid leaking from rear cylinders.
2. Brakes lights light up fine (no burned out bulbs)
3. Fuses carefully inspected.
4. Check engine light is not on (apparently no trouble codes?). I have three 4-position plugs and one 6-position plug near the battery that various sources indicate should be used to show trouble codes. I've jumpered 2 and 3 on all the 4-position plugs, and B and D on the 6-position (tried each several times). Nothing produces any trouble codes on the check engine light at all.
5. Did a complete brake fluid flush--didn't fix. Inspected brake hoses, didn't see any leakage or apparent bulges.
6. No exterior leaking fluid from the master cylinder.
7. The brakes are soft (when applying pressure to the brake pedal), however. They will go about 1/2 way to the floor, and will go a little farther if pressure is kept on the pedal.
I'm out of guesses, except for suspecting a brake master cylinder with bad seals.
I would highly suspect a master cylinder problem. It sounds like you've checked pretty much everything else.
Be sure to make sure that the emergency brake is not on. This is a common cause of the light staying on.
June, 9, 2012 AT 4:41 AM
I am pretty sure the hand/park brake warning light on the dash is also an indicator for the power steering system.
I have a similar problem with mine. When I go over a speed bump or make a left turn the park brake warning light would turn on. At first it was only when I went to a full left turn. Gradually it got worse so that any movement of the steering wheel to the left would turn on the light. Now it stays on all the time unless I am turning right. My power steering fluid reservoir is full but I have noticed a leak on one of the hoses. I suspect it is the power steering pump. The power steering pump has a light weight electrical connection that I suspect is the warning indicator.
June, 22, 2012 AT 2:49 AM
I tried to check my master cylinder. I unplugged the cable, and jumpered the return leads with a wire, and after that also left the circuit open. One way should have turned the light off if the master cylinder had been the problem, but it stayed on both ways.
I'm thinking of doing the same thing with the sensor on the brake pedal now.
I will keep the power steering in mind, although mine seems to be fine.
I would expect my problem to have generated a "check engine" light/error, but mine hasn't. I may just end up taking the vehicle to a shop and having it fixed right.