brake pedal play/clicking

You know, in my Gen 3, up till now I've always thought that was the brake light relay, but I went out in the dark just now and carefully pressed on the pedal while watching in the mirror to see the red light behind the car. The brake lights don't come on exactly with that click, so it's not the sound of the relay. (I guess that's not surprising; the Gen 3 "brake light relay" exists, but it's an electronic thing and I guess it doesn't make any sound.)

By watching the live data in Techstream, I could see that the click was really two clicks at the same time; it's the SMC and SRC valves closing. Interestingly, 'closed' is their "OPS normal" position and 'open' is their "fail-safe" position, but those two valves stay in their fail-safe, open position all the time until you lightly start to press the pedal; only then do they close. I guess that's ok with me; it means if the ECU does fail, most times they won't have to go to their fail-safe positions, they'll just already be there.



But that's a diagram for my Gen 3. Your Gen 4 has somewhat different plumbing:



(annotated by Elektroingenieur).

In yours, I would guess it might be doing the same thing with the SSA and SGH valves. The easy way to find out would be, as I did, to watch the live valve positions in Techstream while lightly pressing the pedal and listening for the click.

It is now dawning on me, another thing they changed from Gen 3 to Gen 4. When I first saw that diagram I noticed the two new strange pumps (Elektroingenieur found a patent describing something to do with "sideslip prevention). But until now I didn't notice the change to the way the four brakes are grouped. You can see in the Gen 3 diagram the two fronts are grouped together and the two rears (the same as the previous generations), but Gen 4 has gone with two diagonal pairs.

 

The Repair Manual (more info) describes several adjustments for the brake pedal, including one for free play (stop light switch clearance). I’d expect a dealer at least to check that those adjustments are within specification and that the push rod pin and its clip are properly installed.

 

Mine has been making the annoying click for some time. Never thought about having it serviced. Figured on other cars I probably couldn't hear it over the running ICE unlike the prius

 

I heard a continuous clicking this morning for the first time. It lasted for about a minute as I tried to identify it's source. I had just backed into the driveway at home, and I believe I'd put it in Park, but it may have still been in Drive. The clicking stopped after I switched from either park to drive or drive to park and didn't come back when I moved the shifter to reverse, drive, park again a few times while the car was stationary. I'd just driven about 30 miles.

My brakes have been acting a little stranger than usual after pulling the passenger front caliper to check the slide pin grease, than I forgot to pump the brake pedal before putting the car in Ready mode, being in a hurry to pickup the misses at the agreed upon time.

Will check later, if my new thinkdiag odb2 + app will show any history errors and look at how it want to do the bleed process, if it's available for the Prime, since thinkcar says Primes not supported officially yet with their thinkdiag bt adapter plus the software that is downloaded from the App Store or Google Play.