Very faint clicks at stop from brake actuator

2011 150k

Very faint clicks when at a stop from brake actuator. Had wife pull the car into drive way, gear in D, foot on brake, popped the hood and found this faint click (~1x/s) coming from brake actuator area. Quite difficult to pickup even in a quiet cabin.

Brake works fine. Actuator pump seems to run at same duty cycle as it always has.

Last brake fluid flush was probably > 10 years ago simply due to the complexity of flushing this system (have techstream and know the process)

Actuator must have a high pressure accumulator of course. No idea how much pressure is maintained. Need to read up more. Currently spending accumulator diagnosing effort on an Audi DSG transmission which has a 400 PSI campbell soup can sized accumulator to drive its actuators and clutch packs haha.

Anyone encountered before?

 

Good idea, I'll check this more carefully. Familiar with Prius running accumulator pump when first open the driver door in garage. I don't recall the faint clicks but will check carefully.

I guess maybe an additional test... Run the car to get engine tranny hot. Park, wait awhile, open the door to trigger accumulator pump, see if click occur in case related to a hotter engine compartment

 

Thanks! Will bring a stethoscope to the test and see if can pin point click to any brake lines can get access to.

 

Thanks its been awhile but I recall the actuator is kind of a sealed unit. I'll run techstream later and see if any per brake line sensor to look at. Will report back but might be awhile. Still tied up debugging Audi's crazy DSG transmission with electric motor pump+accumulator ATF pressure for shifting haha. Snooping the electric motors + sensor data... Far from the days of running a simple geared ATF pump...

 

Cool thx! I see ~$750-$800 at some Toyota dealers selling online parts and of course wait for their frequent 25% off + free ship So we'll see how my faint click evolve...

 

Decided to record some data today (2011 Prius II, 151k miles). Here is accumulator pressure without touching brakes and pressing brakes 4x.

• Car in Park, Parking brake on
• Power button in ACC mode
• Without touching brakes It takes 1.5min for accumulator pressure to reach the trigger point for pump to recharge (~3.7+V to 3.23V)
• When pressing brakes, Accumulator needs charge up btw 1-2 brake press

Incidentally, diagnosing an 17 Audi A4 dual clutch transmission (DSG) also using a pump accumulator (also nitrogen filled for counter pressure) for clutch and gear shifting pressure (no mechanical hydraulic fluid pump in this tranny). Accumulator similar size as Prius brake accumulator (campbell soup can size) and a fully charged accumulator last about 1.5 shifts before trigging the pump to charge up again. So it seems quite similar. Audi DSG has study guide outlining accumulator pressure window : 28 bar (400 PSI) is full, pump is triggered at 24 bar (350 PSI) Have some nice graphs if curious ( link )

• My brake fluid reservoir level seems to not have moved
• No codes
• When pressing brakes, was able to get the faint clicks to occur a couple of times but not so repeatable
• Stroke simulator seems to also make some noise (louder than the faint clicks) but noise stops if applying a little more firm foot pressure. I think there must be seals etc. My 2013 Tesla brake pedal also made noise since 10k miles old, some kind of seal on its stroke simulator. Been that way for > 10 years and 80k miles.

Anyhow, seem my particular car might be still quite early in accumulator/actuator failure. Maybe occurring in many cars without people noticing. It is quite faint clicks.






This post ( link ) has brake hydraulics diagram with sensors location etc. One of the 2 stroke sensors is the one on the brake pedal. Not sure where the other one is (simulator?) Anyway, they are inverted signals which I suppose is probably good (match haha).

Here is a video ( link ) of teardown of Gen1 or Gen2 Prius brake pump/accumulator, actuator/ABS etc. Looks like a sensor is on the simulator (3m17s mark)

 

Looking at the accumulator pressure recharge on the 2nd graph, looks to be ~3s. BTW, the Audi tranny pump (similar motor size as Prius accumulator pump) went from 600 RPM (this pump has dual pressure output including a low output to cool the dual clutch) to 3k RPM for 2s to bump the accumulator pressure from low trigger point 24 bar to full 28 bar.

It does run quite a bit longer when first open the driver's door but I assume accumulator pressure is probably quite low in this scenario.

At least while parked in ACC mode, 1-1/2min from 1st graph. This is with accumulator already charged up after opening driver's door. Then gradually fade in 1-1/2min to the pump trigger point.

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It seems nothing out of the ordinary so far. I don't notice the brake pump come on more than the past... but its one of those gradual things... probably forgot what a new car was like... much like VW turbo-charger waste gate shaft sleeve wear haha (sorry just been emersed in Audi's 1/2 time haha) when VW/Audi guys get new turbo... its like a whole new car with the old turbo losing boost with waste gate shaft sleeve wear.