My brake warning light comes on at a half lit or less brightness intermittently, and I can't find anything in my book on what this is supposed to indicate. The brakes themselves are fine and the brake fluid level is fine. It seems like there is a sensor in the top of the master cylinder reservoir cap and I wonder if that's the culprit?

Any suggestions on where to start "sniffing" would be appreciated.

 

I believe the sensor on the cap is just a float switch type sensor. I could be wrong, i havent pulled one out to examine it.
could be the sensor, or the bulb in the cluster. i would pull both to see if there is anything funky looking.

 

I guess my main question is what is the half-lit brake warning light supposed to indicate (assuming sensors, etc. are all working properly)?

 

its probably a short or a bad connection. taillights do this sometimes too, either bad fuse or bad bulb.
i wouldnt assume that everything is working properly, its most likely something really simple

 

Again, I just want to clarify what the half-lit parking brake warning light is supposed to indicate. This is my first time owning a Toyota after a while and I vaguely remember this warning, but don't recall if it's related to the brake lights, or brake fluid level, or some other indication.

Again, it is the parking brake warning light that is coming on at about half voltage.

 

I have had this a few times over the years and it generally has been the charging system on it's way out. Why the brake light comes on and not the battery/charge light, I can not explain, but I've been through it a few times now. The brake light goes off when you increase the rpms, yes?

In my case it has had nothing to do with the brakes.

 

That's interesting. It seems like I'm getting good voltage, but I'll keep an eye on that.

It isn't affected by RPMs, just seems quite random with no noticeable patterns. Comes on for a length of time then goes off for a length of time.

The only real nuisance about it is that it doesn't allow me to engage the cruise control while it's on.

 

If you have a hanes or chilton book, check the wiring diagram and see if those two things are on the same circuit. Still seems like a short to me. Possibly a bad ground too

 

when mine is half lit the fluid is low....just my .02

 

Same here, on all the toyotas ive had, whenever the brake light is partially illuminated it just means its reading low brake fluid. If the brake fluid looks full then that means your sensor is just dirty.

 

X3 - for me, if the fluid is just a tick low, the light starts flickering. Even if it looks topped off, pour some brake fluid in and make sure it's up to the tippety-top. It takes more fluid to top it off than you would think.

 

This is more what I suspected. Even though it's full, I will see if I can top if off any.

Also, I'm assuming the sensor for this is the one that's in the actual reservoir cap? Is there a special way to clean this sensor or just clean it up with electrical cleaner?

If none of these steps work, should I consider replacing the sensor or is it one of those things that either works or it doesn't?

 

I'm not sure but after I topped off the brake fluid my light has never come back on. I have a 94 4Runner with 190k miles on it.

 

I would say electrical cleaner or move the sensor up and down and pour brake fluid over it. shoud do the trick. good luck

 

You are only supposed to top off the fluid when you replace the brakes. Fluid level drops as the brakes wear...this is normal. Assuming the reservoir float switch is working properly and you have no leaks, the brake light will begin to come on when the brakes need to be serviced.

With that said, most people just top it off and check the brakes every once in a while.

Float switch repair:

https://www.yotatech.com/forums/f128...e-lamp-186984/

 

very good point you woulnt want to push brake fluid out all over when up push the calipers back in....LOL....been there done that!

 

My brake pads are fine right now, although I"m sure I will replace them at some point this summer. Hopefully, I'll be able to figure this out meanwhile.

When I replace brakes, I always keep an eye on the fluid level before compressing the caliper and remove fluid if necessary (a large syringe works great...)