Deceleration/braking downshifting?

J

Jarpee28

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2013 Mazda CX-5 GT AWD 6AT w/ Tech
Just picked up my 2013 AWD GT and I have a question about the shifting of the automatic transmission during braking and decelerating. Today I was braking down a fairly steep grade at about 25mph or so and as I picked up some speed the tranny did not shift to the next gear, instead the rpms went to about 3500 with only the brake being applied. Is this normal? Like a safety feature or something? I also noticed when I am coasting from about 22mph to around 18 trying to save gas there is a down shift which causes the rpms to go to about 2100 or so and causes the speed of the car to decrease. Again, is this normal? I used to have a ford truck and I really never felt the down shifts while coasting at all and the rpms would stay around 1300 or so when going less than about 35mph when coasting or braking. Any thought?
 
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Yes, it's normal for this transmission. It's providing engine braking and mimicing the behavior of a stick shift. When you reach the bottom of the grade and get back on the gas, it's already in the correct gear for acceleration. And to quote Martha Stewart, "That's a good thing."
 
Just to elaborate on what Paris said:

Yes, normal and good behavior. When you apply the brakes it tells the cars computer you are in slowing down mode and it downshifts to save wear on the brake pads. Also, the engine will inject less (to no) fuel in this situation because the engine is being turned by the momentum of the vehicle. If I am in "Auto" mode and the car downshifts when I want to be in a higher gear for better coasting I will switch to manual shift mode. Another technique is to lightly press the accelerator pedal and the car will shift to the next highest gear.
 
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Some what amuses me that there are people these days that have on idea what engine braking is. Hell, it's one of the questions for all driver/learner's permit/license tests nationwide.
 
I find the shift tollerance in cruse control to be much wider in M rather than D. In rolling hills in D it downshifts after about 1-2 mph drop from cruise set speed and on the other side of the hill is downshifts for braking about 1-2 mph higher than set speed. I just move to M and the mph allows a much higher range before changing gears which I think is more efficient and less wear on the transmission but it may lug the motor a bit more going up the hill...
 
Thanks for the explanation mike. Pistons, I understood what engine braking is, it is just way more prominent in the cx5 than any of my previous cars or my fianc's Hyundai. Do to guys ever switch to neutral when you will be coasting down a long hill say on the interstate? I also used to do this in my truck.
 
Jarpee28 said:
Thanks for the explanation mike. Pistons, I understood what engine braking is, it is just way more prominent in the cx5 than any of my previous cars or my fianc's Hyundai. Do to guys ever switch to neutral when you will be coasting down a long hill say on the interstate? I also used to do this in my truck.
Click to expand...

Shifting into neutral is a way to keep your speed (or go faster depending on grade) using very little gas to keep the engine running (we get about 100mpg at around 40mph in neutral). With the manual trans, I can shift into 6th gear and use no gas crusing down the hill if I blip the accelerator for an instant. Any speed lost while cruising in gear costs a bit more gas to accelerate back to speed though since accelerating uses a LOT more gas.

Since it seems you have the automatic, shifting into neutral or playing with the manual mode might be interesting if you really want to try and get a few more miles per tank and have a lot of hills.

I drove a rental car CVT trans Rogue on a trip last year and it was really weird to not have any engine braking going downhill. We were going down a mountain and I had to keep on the brakes had no option to shift into a lower gear. I can see that there are some advantages with CVT but you give up a lot of control.
 
Jarpee28 said:
Do to guys ever switch to neutral when you will be coasting down a long hill say on the interstate? I also used to do this in my truck.
Click to expand...

I would sometimes do this in older vehicles (if the hill wasn't so steep as to require braking) but it's not needed with the CX-5 because it's smart enough to cut fuel to the engine while coasting downhill in gear. When I return from the ski area there is a stretch of road that is entirely downhill for a number of miles. I leave the engine in gear so I do not have to ride the brakes. This is a situation that I am glad the automatic transmission CX-5 has a manual gear selection mode because it allows me to select the gear that will allow me to coast at the speed appropriate for the situation. More often then not, when I get to the bottom of the hill my Average MPG is higher than it was at the same point before I climbed the hill. And the cold engine light is still on when I get to the bottom of the 8 mile hill (indicating that the engine has not been consuming fuel while in gear for much of the 8 mile drive). If I were to let the engine idle in Neutral and coast for the 12 or so minutes that it takes to get to the bottom of the grade the engine would be consuming fuel the entire time and the cold engine light would turn off before I reached the bottom of the hill (indicating more fuel was burned). Plus, my brake wear would go up drastically.
 
MikeM. said:
I would sometimes do this in older vehicles (if the hill wasn't so steep as to require braking) but it's not needed with the CX-5 because it's smart enough to cut fuel to the engine while coasting downhill in gear. When I return from the ski area there is a stretch of road that is entirely downhill for a number of miles. I leave the engine in gear so I do not have to ride the brakes. This is a situation that I am glad the automatic transmission CX-5 has a manual gear selection mode because it allows me to select the gear that will allow me to coast at the speed appropriate for the situation. More often then not, when I get to the bottom of the hill my Average MPG is higher than it was at the same point before I climbed the hill. And the cold engine light is still on when I get to the bottom of the 8 mile hill (indicating that the engine has not been consuming fuel while in gear for much of the 8 mile drive). If I were to let the engine idle in Neutral and coast for the 12 or so minutes that it takes to get to the bottom of the grade the engine would be consuming fuel the entire time and the cold engine light would turn off before I reached the bottom of the hill (indicating more fuel was burned). Plus, my brake wear would go up drastically.
Click to expand...

I can only speak for the 6MT but the engine doesn't always "not consume any fuel" when going downhill in gear in all situations. The best way to know exactly what the engine is doing without vague guesswork is to get output from the CPU.
 
Sounds great in theory, and that most likely will never happen here (getting output from CPU).
 
CX-SV said:
Sounds great in theory, and that most likely will never happen here (getting output from CPU).
Click to expand...

It's not just theory and many people can do it. Anybody with about $20 (I paid $24 for my bluetooth adapter but but there are cheaper ones) and a smartphone can do it. I posted previously about the Torque app and the bluetooth adapter. I can see a live graph of my mpg so can see exactly when the engine cuts gas and when it doesn't along with the all kinds of other data from the CPU. I don't drive the CX-5 much but what I really want to find is the custom pids to monitor the intake and exhaust valves. Maybe some Mazda3 skyactive guys might have more experience to find the custom PIDs for skyactive? Or maybe we can get more CX-5 people fooling around with some pid monitoring apps.
 
Good to know it's not just theory and like I said, not likely to happen here.
 
I am partly interested in scan tool...

But, I would prefer a dedicated device, as opposed to an app on a smart phone, such as the Dash Hawk I use in my MS6.
What is the refresh rate w/ these apps and bluetooth OBDII port devices?
A dedicated device with support is optimal, seeing as parameter algorithms differ per make and model. It took some time for MSD to optimize firmware for the Mazdaspeed community for their DH to display true PID values...
 
I have a dedicated device scan tool that I would be willing to sell cheap or give to my neighbor. I used it only once before to read a check engine light code on another car but smartphone apps can do so much more now.

The refresh rate for the Torque app is at least once a second. The fuel economy is updated live and goes up to 255 instead of the 99 seen on the dash. There are literally dozens of other PIDs which work right out of the box from intake temps, to cat temps, to A/F ratio, engine load, intake timing, etc.

It is also integrated with google maps and will log your trips along with your speed and show them on the map. It is really amazing what can be done now and more and more people will find out about it over time.
 
Buger said:
I have a dedicated device scan tool that I would be willing to sell cheap or give to my neighbor. I used it only once before to read a check engine light code on another car but smartphone apps can do so much more now.

The refresh rate for the Torque app is at least once a second. The fuel economy is updated live and goes up to 255 instead of the 99 seen on the dash. There are literally dozens of other PIDs which work right out of the box from intake temps, to cat temps, to A/F ratio, engine load, intake timing, etc.

It is also integrated with google maps and will log your trips along with your speed and show them on the map. It is really amazing what can be done now and more and more people will find out about it over time.
Click to expand...
So how does one plug a smart phone into an OBDII port? Or am I missing something?
 
paris1 said:
So how does one plug a smart phone into an OBDII port? Or am I missing something?
Click to expand...

You just plug the small bluetooth adapter into the OBD2 port then pair your android device (phone, tablet, etc) with bluetooth capability to the adapter. I'm not sure if people have tried directly connecting their smartphone to the OBD2 or if Torque will work that way.
 
Bopper said:
Does this Bluetooth device have a name? Can it diagnose and clear CEL's?
Click to expand...

Below is the exact bluetooth adapter I got for $24. I remember seeing ones as cheap as $10 or so and there are others which can be a bit more expensive also. I mainly got the one I did because of the good reviews and good posted experiences along with a decent price.

https://www.amazon.com/dp/ (commissions earned)

Below is a link to the Torque app for android. You can definitely diagnose and clear CELs which is why I don't really need my other plug in scan tool anymore.

https://play.google.com/store/apps/details?id=org.prowl.torque&hl=en
 
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