Howdy! I had an issue pop up back in October where my e brake light came on and would randomly turn off, but after a few weeks of this the light stays on constantly. If I leave the truck off for a while, or turn the engine off and pump the brake pedal, the fluid returns to the reservoir and will eventually reach the MAX line.

When the pump on the master cylinder turns on, it takes several attempts to fully prime the brake system and sucks down half the fluid. The fluid level always returns to the MAX line if the truck is off long enough so it doesn't appear that I'm losing fluid.

I'm providing links to the videos I took of the problem in action at the bottom of this post.

I dug through the forums here and found out that the brake light is indicating that the pads are too low and need changed. I recently replaced the front pads, however upon checking the rear pads it was clear they need to go.

Today I installed the new rear pads expecting the fluid level to be back to normal when I turned the truck on, but the same problem still persists.

I bled the brakes all around to make sure there wasn't any air or old fluid in the lines so there's now fresh fluid in all 4 calipers. While doing the bleed I checked for wet spots on the calipers and found none.

At this point I'm not sure what the issue could be and hoping someone here might be able to point me in the right direction. I'm guessing I may need to have a full system flush to ensure there isn't any air in the system.

Thanks in advance! Video links below:

Video of master cylinder pulling the fluid from the MAX line: Shared album - Cody Stokes - Google Photos

Video of fluid being pushed back into the reservoir when engine is off: Shared album - Cody Stokes - Google Photos

ABS system accumulator will be fed by energized pump. Did you perform ABS bleed?

I don't believe I did. I just looked this up and found this handy video (https://www.youtube.com/watch?v=nQRn...annel=2CarPros), I do not have the computer I need to trigger the ABS system so I probably need to take it to my mechanic and have him do it for me.

I didn't find any straight forward forums specific to the 4th gen 4Runner about this process, but if you know of one, can you please share?

Have you checked your E-brake cables or the actual E-brake Drums? They don't use anything hydraulic so that may be why it persists. Mine got bad and the light wouldn't shut off because it thought the E-brake was applied. (my cables rotted off the truck. least it was an easy fix.)

Also is there a buzzer when the fluid drops? There should be one if it drops too low or the fluid temp gets too high. I've heard it from experience many times

It's not a ebrake cable issue since the light goes away if I add more fluid or when I accelerate and the fluid level covers the sensor for a brief second. An ebrake cable issue probably wouldn't result in the system sucking down a ton of fluid when it primes so I'm betting there's something going on inside the ABS module that needs bled.

I think it's worth your time to get Techstream and do the ABS bleed yourself with another helper vs paying a mechanic. There are threads on how to install Techstream since it's not too straightforward IIRC. Additionally, the Techstream allows you to speak directly to the ABS ECU and there might be fault codes that will give you some clue as to what might be happening. At least this way, you're not guessing while wasting time!! Another cool thing about Techstream is that you can see when you step on the break or pull the E handle and such because you see what the ECU sees! It's a very powerful tool.

ABS valve block bleed:

https://www.youtube.com/watch?v=JM5A8PnjS7I

How does the pedal feel before bleed? Braking action any good?

Wow that's a lot of mess he made. After a normal bleed without the tool resulted in a much better pedal feel (granted I replaced a failing master cylinder) but the system just drinks a ton of fluid when priming since I suspect there's just air in the ABS unit that's getting compressed when it primes.

I dropped the truck off at my mechanic to do a full bleed using the computer. Will see what happens when I get it back.

I'll look into this device but I don't expect to have to do this again assuming my replacement master cylinder doesn't fail.

You can throw parts at the issue, which is quite common. However, knowing the ins/outs of your rig that you intend to keep for years is beneficial all around!

Hope this works for ya!!

Doing the ABS bleed was the solution. My mechanic knocked it out for just under $240 with labor and fluid. Honestly I'm ok with that cost given how important a properly working braking system is.

Thanks everyone for your help and input!

Glad you got the issue resolved!

Question, did you determine what caused the issue to occur, I wouldn't think it "happened" all on it's own?

I installed a remanufactured master cylinder and didn't fully bleed the system. I didn't have the tool to actuate the ABS system during the bleed so good to know for next time I do a brake job like this that I'll need to do extra work.

That makes sense, it appears that the remanufacturer didn't bench test the unit which would purge any air out of the unit, I say that because I just replaced mine a few months ago with a brand new unit and had no problems with the ABS, just had to bleed the master cylinder itself and all was good, I'm sure Toyota makes sure the units are in working order by doing a bench test.

I was however prepared to do a ABS bleed if necessary, I have a SST that will do anything that Toyota's SST will do.