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Discussion Starter #1
Unintended Braking Force

I have an EX-L Nav. When the a/c compressor cuts out in the climate control system, I get a momentary increase in engine vacuum that causes the brake servo to increase boost. The result of this is to increase the force of any braking effort and cause the Pilot to "lurch" - making for uncomfortable non-linear braking. This happened the other day in the rain when I was was coming to a routine and non-emergency stop at a red light. The fault caused the driver's side front wheel to lock up and the ABS to thereby activate: nasty.

Has anyone else experienced this?
 

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maybe but not sure

I have noticed that it seems the brakes act in a very nonlinear way at times. Like my foot doesn't move but all of a sudden the breaks grab harder and I have to release them quickly to get back to the same level of resistance. I will try and pay attention to what is happening with the climate control system at the time.
 

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ditto

I have noticed the same phenomena - hit the brakes for a gradual stop and a second or two later, it feels like you are really standing on them.

I thought maybe they were heating up and starting to grab harder.
 

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If you are on downward incline when braking, it may be the downshifting of the transmission. I think it may be the grade logic stuff kicking in. I've lightly touched the brakes, then been jerked forward, too, and that's the only thing I can figure.
 

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jay said:
If you are on downward incline when braking, it may be the downshifting of the transmission. I think it may be the grade logic stuff kicking in.
Indeed, what he said-
 

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Re: maybe but not sure

axjms said:
I have noticed that it seems the brakes act in a very nonlinear way at times. Like my foot doesn't move but all of a sudden the breaks grab harder and I have to release them quickly to get back to the same level of resistance. I will try and pay attention to what is happening with the climate control system at the time.
Mine does exactly the same thing. Never experienced this before in another car. Just thought it was what the Pilot did...
 

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Grabby brakes in wet weather is actually pretty common with rear drum brakes. The lining dust builds up on the drum/shoe surface and grabs when wet or damp. The disk brakes of the Pilot should not have this problem, but it's still possible the particular pad material gives off dust that locks the brakes up when cold. If the problem is worse in the rain or high humidity, that may be the cause. Replacing the brake pads with a different type material and cutting the glaze off the rotors should fix it if that's the problem.
 

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Morris, I was just about to post my experience with the brakes when the A/C is operating and I caught yours. What I noticed is that, with the A/C on, when I'm stopped at a light, sometimes the brake pedal will "give" just a bit, as though it's slacking. It's hard to describe, but I noticed it only happens when the A/C is turned on.

Don't know what's causing this. I see others have replied, saying that it might be the Grade Logic Control kicking in when going downhill, but since I've experienced something similar to your braking idiosyncrasy, I know what you're talking about.

I'm familiar with the GLC feature in the Pilot and what I experienced definitely had nothing to do with it. Reading mmay and axjms posts, sounds like what they experienced is the GLC kicking in though.
 

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I have notice the exact same thing RipRock described on my Pilot too. I thought it was me stepping on the pedal at an angle or something.
I've also noticed the interior lights dim very noticably when the AC kicks in as well.
 

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Discussion Starter #10
At about 15mph, shift into neutral and gently brake with your left foot. As you are doing this, blip the throttle momentarily to about 2,500 RPM. As the engine returns to idle you will get an observable increase in braking effort as your left foot sinks on the brake pedal.

It would be interesting to try doing the same thing except manually switching off the a/c instead of blipping the throttle while braking in neutral.
 

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Downhill braking - non-linear

My '98 Acura does this very consistently on the same downhill exit ramp, every day I drive it. I believe it is the grade logic, and in my case I have had it happen whether or not the A/C is on. The only difference from the Pilot may be the speed, which occurs around 30mph in the Acura.

If you can reproduce the same action in the future, watch the tachometer (safely) just before you think the shift will occur. You will likely see the rpm jump as the deceleration increases. I think it's a Honda thing.
 

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Here's a definition I pulled from an car review.
The Pilot uses "Grade Logic" Control to reduce shift frequency. Grade Logic is a version of a fuzzy logic algorithim that adjusts to different changes in driving.

When going up a steep grade, Grade Logic automatically downshifts and holds in a lower gear, so the Pilot maintains a constant speed. When traveling down a steep grade and braking, Grade Logic automatically downshifts to help provide engine braking, giving you more control.
Some owners have reported the GLC shifting gears on slighter slopes while in commuter traffic or while breaking for traffic.
(check here too)
 

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ABA

Well as far as I'm aware our pilot has a feature built into the breaking system called a Active Break Assist. This feature is there for greater stopping power as in emergency stopping. what it is suppose to do is put a little more force when you step on the break. The engineers claim that it is suppose to help avoid rear end collisions but giving you that extra stomp that you should have applied in the first place. They claim that most people hesitate to step on their breaks in hard stopping situations, so they let let the computer compensate for this hesitation. I think it is a good feature but I too have notice a variation in breaking with the A/C. In my experiences, I've noticed being stopped at a light or something then when compressor cuts out the car Starts to move forward as though I've released the breaks a little. This easily overcome by just applying a bit more pressure. Annoying I aggree. I surely would not attribute this in no way to the Grade Logic Control because this feature has nothing to do with the breaking system. GLC works from the transmission. Just my 2 cents.
 

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Do notice it mostly on the decline

I think Jay and the rest of you guys have it exactly right. Now that you mention it, the Pilot does really grab when I am going down a hill with a stop sign at the bottom of it. Those conditions would be perfect for the GLC to kick in. I tend to charge stop signs though so it could be the emergency brake assist but I doubt it. I am going to watch the tach next time I go down that hill and let you guys know what I find out. Thanks
 

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Yep, that's what I thought, axjms. As I stated in a reply to Morris, I thought that what you and mmay were describing was the GLC kicking in. I'm very familiar with the feature and once you get used to it, it's a veryhandy and intelligent feature to have on a car when going downhill.

What Morris and I have experienced is an anomoly with the brakes when the A/C is turned on. The brake pedal "give" I spoke of is something I've experienced at a complete standstill while at a redlight, so, it's definitely not the GLC.

I just hope what Morris and I are experiencing isn't or doesn't turn into a problem like my dad's Lexus LS400. Whenever he turned on the A/C, the RPM went up, thus requiring bigger braking force to stop the car. He did get it repaired, but that was after his warranty expired and cost him alot of money. Hope that doesn't happen to me.

Even if I take it to a dealer right now, since the brake pedal "give" doesn't happen every time I have the brake pedal depressed at a stop with the A/C turned on, I know what I'll hear, "we won't check it out unless we can duplicate the problem".
 

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Discussion Starter #17
Thanks

Thanks for the great replies. I'm going to pay more attention and see if the "grabbing" is happening when braking going down an incline. Will post back.
 

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Discussion Starter #18
It's the GLC

Drove this morning with the a/c switched firmly off. I braked on a downhill to stop at a red light and, sure enough, I experienced the extra retardation as the transmission downshifted. Not an entirely comfortable feeling - I was always taught to drive (& brake) smoothly & fluidly...
 

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Or you can try this. Move the shifter to neutral before you slow down to a hill and apply the brakes. It should be like any other automatic car except the Honda. I do like the downshifting... I wish my A6 had this future!
 

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Grade Logic

I recently experienced the grade logic control when traveling downhill from the mountains. All of a sudden, the Pilot downshifts when I let off the gas on a downgrade. I was kind of baffled at first and thought that it was the altitude making the vehicle act weird. Then I remembered reading this thread about grade logic...

Thanks!:29:
 
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