ive been reading the forum off and on for awhile now at the various actuator posts. so back in 2020 i took my 09 prius to Toyota to replace the actuator.....3000$ 155K previous to that the actuator was running 5-10 seconds every 5 seconds. maybe 6 months ago it got on my minds radar that im hearing cycling again, but its possible its always been there. so i installed a counter and hour meter back in late 2024. today im at 274K im averaging about 415 cycles per hour, 7500 cycles per tank of fuel and the actuator runs between 2-2.5 hours per tank of fuel. since January 1, the actuator has run about 13 hours total. it sounds like its coming on for 2-3 seconds, off for 6 seconds. what cycle counts have you noticed on yours? does yours cycle? and when the actuator is working properly, is there any routine cycling at all? when yours failed, what kind of cycles did you observe before the failure?
I believe that no one pays attention to the cyclical operation of various systems until these systems light up the failure lamps on the dashboard or stop working. But if you have such an opportunity, then inform us about changes in operation with increasing mileage of the car.
If you are talking about the pump in the brake actuator assembly, it really shouldn't "cycle" if you are not using the brakes. The pump runs to push brake fluid into a storage "tank" known as an accumulator. Inside is high pressure nitrogen sealed off by a flexible diaphragm. Pumping in fluid causes the diaphragm to compress the gas further (an air "spring"). So the brake system has a volume of fluid at a couple thousand psi to use. The ecu controls solenoid valves to direct that pressurized fluid to make the brakes work. There's a sensor to monitor the accumulator pressure. When it drops to a certain point (about 3.2V on the scantool) the ecu turns the pump on, then off when it reaches a higher point (about 3.6V). Under normal conditions, the only significant "use" of pressurized fluid should occur when you step on the brake pedal. The system will bleed off pressure over time (ie, very slow internal leakage), but that takes place over a few hours. On my 2006, accumulator pressure drops by less than 0.1V in 30 minutes (ie, it didn't turn the pump on at all). With "normal" firm brake use, the pump cycles on every 2-3 stops. So, are you actually monitoring the correct thing? Personally, I would get a capable scantool to look at the accumulator pressure sensor (ACC in the data list). If it is, then something inside the actuator is leaking. Posted via the PriusChat mobile app.
On a new Toyota hybrid, the pressure must drop overnight, because the pump comes on when you open the driver door in the morning
Yes I'm monitoring the actuator pump, they are notorious for going bad, it's all over the forum. It's probabally the #1 part removed off of the junkyard Priuses. Ice read that there is an internal leak that drops pressure causing the pump to keep cycling on to maintain pressure. I'm thinking about doing a test where I modify the power circuit to supply power when I press the brake pedal and then it can pressurize it when the brakes are needed to preserve the pump and motor. It wouldn't be hard to do. Just create a circuit that engages a relay when the brake is pressed. I'm still thinking about it because I really don't want to spend another 3 grand on the actuator.
It would be a bit late waiting until you need brakes to pressurize the system. I'd think long and hard about modifying a critical system in such a way. The OEM design already has checks and balances to ensure the pump does not run more than it needs to. If you have a system behaving usually, you might look into it further to ascertain why that is.
I understand the failure, just surprised that you have problems with a new OE actuator so soon. I see a number of Gen 2 with lots of miles on each (including my own), and none have had this happen - yet. I also get the money thing, but what you suggest won't work, because it takes time for the pump to build enough pressure for the system to function. More so when there's "lots" of leakage. You need the brakes to work right when you step on the pedal, not 10 seconds later. Posted via the PriusChat mobile app.
I'm surprised the new factory actuator is having issues because by 2020 I would think Toyota would have solved that problem, that's why I'm curious if anyone has a properly working system and it still cycles. The brake relay to actuator mod would be tested out well before any major road use. I do get what you are saying, needing time to build pressure might not be safe, tho if the actuator only affects the rear brakes as someone indicated, that's only maybe 20% of the stopping power. If I do that mod, I'll report my test results here.
I'm just concerned the pump will eventually fail from running beyond it's designed limits with all the cycling. If I did the mod I would test it out well in a parking lot near me at night when no one is there, that includes getting up to a good speed and slamming on the brakes to see what kind of delay there is. There could be an issue with the computer system too with that mod. If I do it, I'll report the results here
It is not supposed to cycle the way you describe it. Most of the metrics you listed don't really have meaning to most except 415 cycles per hour is not right if one cycle equates to the normal 3-4 second burst of rattlesnake noise. With the car sitting idle at most, you would expect maybe 1 to 2 every couple of hours. In normal driving a burst every 3 or 4 brake presses plus one when you open the driver's door in the morning and another some minutes after you've shutdown for the day. I do believe that once the car has fully quiesced for the day it does not run the pump again until you next open the driver's door and it will only do that if it needs to. So either you have a problem outside of the ABS unit or your unit is defective – which, as others have said, is uncommon. It's over to you to work out which it is in your case.
Does the ABS have a serial number, date code, or actual date stamped on it somewhere? I'm wondering if maybe whoever did this service pulled an ancient unit off the shelf. "New" as in "unused", but not "new" as in "recently made". I ran into that "ancient unused unit" problem recently with an OEM (really, straight from the manufacturer) "new" laptop battery. It had been made 5 years earlier and was visibly swollen. Of course it went right back.
Same as guy mann on a 2012 v with the brake booster assy changed in 2019. It would be 3 seconds too late You lose all power assist on all wheels plus abs and traction control. Stopping distances would be far longer.
