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Background: 2012 Honda Civic EX, 5-speed automatic, with no mods except a non-stock tire (ran over a large bolt). I keep it maintained per the manufacturer's manual and always see the Honda dealership that sold it to me new for maintenance. 20k miles.

Sometimes when I am going down an incline at about 65 mph and I need to brake a moderate amount (decelerating about 3 - 4 mph per second), my engine will rev up significantly. For example, if my cruising RPM at 65 mph is about 2100 RPM, it'll kick up to 2500 - 2800 RPM when braking, and only back down to about 1500 RPM once I either step on the gas again, or reach a very low speed (under 20 mph).

What is going on? Is the car shifting into a very low gear in anticipation of stopping very fast? I usually brake just enough to keep from running into the car ahead of me, and although the brake pedal isn't nearly fully depressed (like I said a "moderate" braking), I rarely have to bring the car to a full stop when I'm in this situation.

It seems fuel-inefficient to run the engine at 2500 - 3000 RPM for a good 15 or 20 seconds when I'm actually asking the car to decelerate. In other automatic cars I've owned (much older; 1997 and 2002), the engine's RPMs just gradually decline the slower you go. Neither my Civic nor my older cars use a continuously variable transmission. I am unaccustomed to this behavior and am looking to see if it is abnormal or something that this car just does because that's the way it's designed.

Update: Here some other people appear to be having the same problem.

For the record, I always drive with the "Econ" button ON and am applying steady brake pressure, not "pumping". It may be "Grade Logic" as one of the posters on that forum put it.

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Regarding fuel efficiency: when a modern fuel injected car is going down a reasonably steep hill and the accelerator is released, the car goes into "overrun" mode, and the flow of fuel to the engine is essentially shut off. So even though your RPMS have gone up, you're getting phenominal gas mileage (it's theoretically infinite at that moment!). –  mac Jan 17 '13 at 23:19
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up vote 5 down vote accepted

Although automated manuals are becoming more popular, the 2012 Civic (from my 2 seconds of searching) appears to be a normal automatic.

Even still, I'm guessing your vehicle may have the sensors and programming necessary to determine that it's descending an incline and is employing engine braking to help you slow down. What it sounds like it's doing is putting the car in gear to allow the drivetrain and engine to add some drag to the car's momentum.

My 2012 Focus does this--but it has an automated manual. Which is an awkward term for a manual's clutch and gearshift that is computer controlled.

I guess a good question would be: Does the car feel like it takes more or less braking when this occurs? If it takes less, the car is helping you slow down. If more, it might be a malfunction.

Another question: If you were to let off the brake when it revs up, do the revs go down again? Try not to fly off cliffs or anything if you try that.

If the engine is braking, this is not going to use any fuel, with exceptions for say, when the car isn't warmed up, and any other rules that it may have.

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Yes, I think the 2012 Civic does have some form of engine braking and that may be the reason. So it's a safety feature because I can slow down extremely fast, even going down an incline, if needed -- right? That's fine and dandy, but I go down a very steep incline (steep enough to make my ears pop) at about 60 mph every day on the way home from work, and the incline is a very flat paved road (nowhere near any cliffs, thankfully) about 2 miles long. I often have to brake because people often slow down to merge rather than speed up, and there's an exit at the bottom of the hill. –  ÃŁŁǫǛȉЖΦΤїҪ Jan 17 '13 at 21:13
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From that comment you posted on your question, it appears it does have this "Grade Logic". It's probably mostly a safety feature: to reduce brake temperatures. It will not decrease your stopping distance any more than the same car going the same speed without the feature--assuming brake temps are the same. –  Nick Jan 17 '13 at 21:16
    
if it has a lockup torque converter, you could get a spike when it disengaged. Most automatics use lockup torque converters now for better efficiency. –  Chris Jan 23 '13 at 4:43
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