ABS Actuator - How often is too often?

What you're describing still sounds to me well within the range of normal.

There's a really large range of normal. The accumulator stores enough pressurized fluid to give you twenty or more brake strokes if the power fails, but when the power hasn't failed, it tries to stay filled up near the top of that all the time. It's not as if it lets you go ten or fifteen strokes and then pumps it all back up again. Every, well, maybe few, maybe several, not very many, uses of the brake is when it will run.

That's rough and vague and wide because it depends on how much fluid is used up every time you use the brakes. That depends on how hard you brake. It depends on the condition of the rear brake adjusters and how springy the front caliper rubber seals are. It depends on how flat the rotors are. It just depends ... on a lot of things.

The rear brakes adjust click by click. You're using a little more fluid per brake stroke if the shoes are worn almost to the next click. A week from now, that click may happen, and then you might be thinking "gee, wasn't my brake pump running more often than this?"

Only probably not, because people tend to obsess over the brake pump only in one direction. If you start thinking you're hearing it more often, then you start noticing it all the times you weren't noticing it before, and then it seems like you're hearing it waay more often. But I've never seen a "hmm, is my pump running often enough?" thread.

I wouldn't worry about what you're describing here. If it ever develops a problem, you will have one or more of: warning lights, an annoying high beeeep, or really, really obvious overactivity of the pump.

 

On my Gen2 cars, I notice the actuator come on after every 2 brake presses. I think it becomes a problem when it comes on CONTINUOUSLY without you pressing the brake.

 

This can be checked and monitored using techstream. Accumulator pressure is measured as a voltage. If I remember correctly, the pump runs until it reaches 4.8v. Once pressure drops to around 3.3v the pump starts. I may be off a bit on the voltages, it's been several weeks since I've looked at it.

A good condition unit will have no leakage, but pressure will drop a bit every time the brakes are used. If you see voltage creeping down, with no brake usage, then the accumulator has some leakage. I don't have a hard set amount of time that qualifies as "bad", but at least you can quantify whether it's getting worse. I've seen some where the pump almost never turns off.

 

I'm hoping that after the ABS is blead properly with a scan tool ...
that the motor on for every pedal actuation will disapear...

 

I have my abs pump running 80-90% of the time when I FULLY press the brakes.
I also hear abs pump running sometimes when I release brakes.
I most of the timesdo not hear abs pump running when I slowly & partially press brakes.
My abs pump when it's running, makes the standard buzzer sound for 2-3 secs.
Hopefully this isn't anything abnormal . This is a brand new ABS pump for my gen 2

 

sounds fine to me

 

Weird. Just today when I drove, the pump was running every 2nd or even 3rd time I fully press the brake. So maybe it's all good. Just gonna observe over the next 2-3 weeks.

 

i think what's most important is how long and how often it runs when not using the brakes

 

"Not very often at all" is a good answer, when not using the brakes.

 

I feel inclined to add to this topic, We have several Prius's that I have maintained and repaired for their entire life and yes I do have a scan tool, an almost essential tool. Mine is about a $500 tool. Have 215K on a 2004 gen 2. Never replaced the brake fluid until recently. The pump runs on door open and then occasionally in city driving, Unpredictably, sometimes a few times in 5 minutes, sometimes not any. Have a 142K mile 2008 Gen 2. Really, almost never runs the pump. Also replaced fluid in this one. Replaced pads and shoes all around both cars. When I change from 2008 to 2004, I sometimes notice it at first. Have 2012 gen 3, low miles car with 51K miles. Runs the pump at least as much as 2004. Is a little higher pitch in this car, but a nice pump sound. I was considering running the ABS linear activator calibration process on 2004 car, until we got the gen 3, 51K car, when I decided again it was normal. One thing I have read is people claiming that air bleeding reduces pump running. I don't think this is true unless you had air in the system. Replacing the fluid with a drain bottle with an anti-back flow valve in it, you will not have air in the system. I won't get into which brake air bleeding techniques work and don't work here. However, if you want to do without a scanner with conventional bleeding technique, you may need a pressure bleeder for the left rear. (and unlike one video you do not press the brake pedal. All M'C open to the reservoir when the pedal is released.) I have a lathe so I made my own. The scan program works too but uses a LOT of fluid and requires a 15 amp automatic charger on the 12V battery. The one thing I did notice is that on the 2004 car, the pump is quite a bit quieter after the fresh fluid, as though it likes the new fluid.

 

It doesn't help unless you have gas bubbles in the system. The gas in the bubbles isn't always air.

The system's pressure accumulator is a brake fluid chamber with a bellows inside and high-pressure nitrogen gas on the other side. If a well-used accumulator starts slowly leaking the nitrogen into the fluid, then you start having symptoms of gas bubbles in the fluid, even if you have never done any work that would let "air" in.

Symptoms of bubbles in fluid in a Prius are a little unusual. In a conventional car, you would expect the pedal to feel spongy. In a Prius, that doesn't happen, because the brake line pressures are managed by computer and it just achieves the target pressure anyway, by sending more fluid into the lines as the bubbles compress. On releasing the pedal, the bubbles return to their uncompressed size and the extra fluid is forced back to the reservoir. This means more fluid is taken from the accumulator for each use of the brakes, and the pump must run more often to make it up. Also, the decreased amount of nitrogen on the gas side of the bellows (where it's supposed to be) also contributes to the pump running more often.

Another symptom you may notice is a honk, bark, or quack sound, as compressing or expanding bubbles involve a rush of fluid honking some valve like a saxophone reed as it passes through.

Bleeding the gas bubbles out can alleviate the honk sound and get the pump back to running less often. It isn't a complete fix; you haven't put any new nitrogen into the gas side of the accumulator, so the pump will still be running a bit more often because of the reduced amount of gas there, and you haven't fixed the slow bellows leak, so after some amount of time you are likely to have bubble symptoms again. But when the leak is slow, bleeding the bubbles out can improve things for a good amount of time.

... a scanner. There are fluid passages in the brake actuator behind valves that have to be opened under control of the ECU while performing the bleed procedure; no 'alternative' procedure gets air out of those places, they're just closed off.

However, if all you want to do is fluid replacement (meaning, there are no bubbles in the system you need to get out, and you'll be super careful not to let any in), you can make non-scantool procedures work for that. (You end up with a little of the old fluid left behind in the passages you couldn't open, but the brakes will work.)