Red Brake, ABS, VSC, and (!) Illuminated Troubleshooting

Hi Kayla, welcome to Priuschat! Thanks for the detailed description, that helps a lot.

I think that you have described two different things going on: Firstly, the general brake warning light, which was most likely caused by the low brake fluid. Secondly, the ABS and VSC warning lights, which normally light up briefly when the ABS and/or VSC is activated because of a slipping or bouncing wheel.

The brake fluid reservoir has a sensor that should light up the brake warning light before the fluid level is dangerously low. The brake fluid level normally goes down gradually as the brake pads wear and the brake pistons extend further out of the cylinders, pulling more brake fluid out of the reservoir, and into the cylinders. Normally the brake fluid shouldn't drop so far just from brake pad wear unless it wasn't completely full to begin with. So look for brake fluid leaks, and check brake pad thickness.

ABS can be activated by a wheel slipping so slightly that you don't even notice the slippage before the ABS kicks in. Sometimes just a little sand or oil on the road can trigger it. When that happens, the regenerative braking cuts out abruptly, and sometimes it takes a second before the friction brakes start gripping. That is normal, but then when you brake again later, it should brake normally again.

If the brake fluid level was so low that the brake pump and pressure tank were starved of fluid, then you would have had to press the brake pedal much, much harder than normal. If that was the case, then it might be a good precaution to have the braking system bled to make sure that there are no air bubbles in the system.

In most cases, when a recognized error goes away, after a certain interval the error code is erased from the current error code list, and stored in the error code history list. I'm not sure if that is also the case with low brake fluid, but you might want to double check the error codes stored under history, using the Toyota Techstream diagnostic software.

I hope some of the many Priuschatters more knowledgeable than I will also reply to confirm or contradict. Till then please keep an eye on the brake fluid level.

 

It can be useful to have a short piece of wire in the car that you can use to retrieve the brake system trouble codes right away if those lights come back on. Takes the "what if my OBD reader couldn't get the codes" or the "shop says they didn't get any codes later" complications out of the picture. You use the short piece of wire to connect the Tc and CG terminals at the car's diagnostic connector, and then count blinks of those dash lights, to get two-digit codes. There are other threads about this.

Doesn't give you all the information Techstream would, but way better than not having any.

In the big picture, all four of those dash lights in your title are controlled by the same ECU in the car; it's divided into different functional groups the lights correspond to, and they tell tales on each other, so it's super common to get those lights coming on together.

Usually, when you pull the blink codes, the codes on one of the lights will be telling you something interesting, and the other ones will be blinking codes for "hey, go look at that one."

 

That is kind of worth a further look. The fluid should be at MAX when two things are true: (1) the brake pad thicknesses are all factory new, and (2) the brake system is "zeroed down".

What does (2) mean? Well, the system has a pressure chamber in it, filled up by a pump. If you have started the car (or even just opened the driver's door), the system pumps that chamber up to pressure, using fluid from the reservoir, and so the reservoir level drops. "Zeroed down" is the condition where the pressure chamber is depressurized and that fluid is returned to the reservoir so you can judge the level.

If you have Techstream, there's a utility in there where you ask it to zero down, you hear a click-whooosshhh, and the reservoir level rises; that's where you should be checking the level. Then if you start the car, or tickle the driver's door switch, you hear the brake pump run and you can watch that level drop again.

So it's natural for it to look a little low, if it isn't zeroed down when you look.

The other thing that makes the level lower over time is wear of the front brake pads. The thinner they get, the more the caliper pistons extend, and the more of the system's fluid is staying there in the calipers. In principle, if there have been no leaks, whenever you get around to replacing front pads, you smush the pistons back into the calipers, and the reservoir level goes right back to where it left the factory.

The rear brakes on a Gen 2 don't work that way; they have mechanical adjusters that compensate for their wear, so they don't end up holding extra fluid as the linings get thin. (Gen 3 and later have calipers on the rear, so their lining wear does drop the fluid level, just like the fronts.)

So the lowest you should ever see the brake fluid is when (1) the system isn't zeroed down, and (2) the front pads are near end-of-life. If you say your front pads are still pretty thick, but you saw half an inch below MIN, I would consider checking for fluid leaving the system anywhere.

If you have Techstream, one thing you can do is turn the car on, sit in the driver's seat, stand on the brake pedal pretty hard, and watch the pressures on the four brake lines. If you see one that isn't holding steadily high, but is slowly dropping and getting nudged back up (you might hear soft click near the firewall for each nudge), that would be a line and wheel cylinder to go inspect carefully for any wet areas.

I once had an older vehicle where a rear brake line rusted and developed a split, and only the highest brake pressures, from really pressing the pedal, would open the split and make it squirt. The wet area was on the other side of the underbody from where the line was. (Those lines didn't have the plastic anti-rust coating Toyota's lines have.)

By the way, if you ever suspect such a thing, don't go trying to find it in person (say, risking your eyes or other body parts while a friend holds down the brake). A jet of fluid at that pressure can go right inside skin, and make injuries that emergency docs sometimes underestimate, then they turn gruesome later. I caught the one in my old vehicle using a good light, an inspection camera, a strategically-draped shop towel, and watching the camera video from inside while I stepped on the brake.