Gradual braking - computer vs. friction

rflagg · 05-12-2004, 07:48 PM

Just out of curiosity, I thought I'd pose this question to you all to see if you've noticed this as well while driving your car.

This isn't a problem at all, just something that I've been able to notice the more I drive this car.

When you're braking at a fairly constant rate, and you get down to 8-6mph, as long as you're applying constant pressure, you'll actually notice that the car will 'switch' from computer assisted braking to real friction braking. The only way I can explain it is like you can feel it "let go", though it doesn't really let go, it's just switching forms of braking. Of course, before you try noticing this similar effect in your car, make sure no one is in front of you first.

Also - out of curiosity as well - when I was doing the Prius XM mod, I noticed the black box in the back of the car marked something like "Braking unit" or ECU or something - would disconnecting the cabling there (which would be really easy to do if someone knew it was there) disconnect your brakes? I'm not looking to knock anyone off, just want to make sure I do nothing to fiddle with that box. Thanks!

-m.

**efusco** · 05-12-2004, 10:05 PM

Yea, I notice the same shift at exactly 8mph.
I also can feel exactly at the 41-42mph shift from stealth to ICE on each time.

I think disconnecting that ECU would be a very bad thing, but I can't say exactly how the Prius would respond. Note that there are hydrolic fail-safes (actually a triple redundant fail safe IIRC) so that if that ECU failed you could still stop.

siai · 05-12-2004, 10:13 PM

If the "black box" you were looking at was in the rear near the aux (12volt) battery, this is the brake control power supply. It is a capacitor to provide auxiliary power for brake control when the aux battery voltage drops too low. Pulling the plug will get you about 10 different DTC trouble codes relating to the malfunction of the capacitor.

05-12-2004, 07:48 PM	#1
rflagg Join Date: Jan 2004 Location: Springfield, VA Posts: 946 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	Gradual braking - computer vs. friction Just out of curiosity, I thought I'd pose this question to you all to see if you've noticed this as well while driving your car. This isn't a problem at all, just something that I've been able to notice the more I drive this car. When you're braking at a fairly constant rate, and you get down to 8-6mph, as long as you're applying constant pressure, you'll actually notice that the car will 'switch' from computer assisted braking to real friction braking. The only way I can explain it is like you can feel it "let go", though it doesn't really let go, it's just switching forms of braking. Of course, before you try noticing this similar effect in your car, make sure no one is in front of you first. Also - out of curiosity as well - when I was doing the Prius XM mod, I noticed the black box in the back of the car marked something like "Braking unit" or ECU or something - would disconnecting the cabling there (which would be really easy to do if someone knew it was there) disconnect your brakes? I'm not looking to knock anyone off, just want to make sure I do nothing to fiddle with that box. Thanks! -m.

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05-12-2004, 10:05 PM	#2
efusco Troll Slayer Join Date: Nov 2003 Location: Nixa, MO Posts: 17,956 My Car: 2004 Prius Model: Package: #9 Thanks: 91 Thanked 443 Times in 255 Posts Friends: 41	Yea, I notice the same shift at exactly 8mph. I also can feel exactly at the 41-42mph shift from stealth to ICE on each time. I think disconnecting that ECU would be a very bad thing, but I can't say exactly how the Prius would respond. Note that there are hydrolic fail-safes (actually a triple redundant fail safe IIRC) so that if that ECU failed you could still stop.

05-12-2004, 10:13 PM	#3
siai Member Join Date: Mar 2004 Location: Florida Keys Posts: 47 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	If the "black box" you were looking at was in the rear near the aux (12volt) battery, this is the brake control power supply. It is a capacitor to provide auxiliary power for brake control when the aux battery voltage drops too low. Pulling the plug will get you about 10 different DTC trouble codes relating to the malfunction of the capacitor.