jpv7774

I have asked this question before and the replies I got were from people that didnt understand the question. So to be clear...My car when driving on a down hill grade will down shift itself slowing the car down from a sort of run away coasting feel. There are very few times when I like this feature...it is good for very long steep mountain hills but other then that I like my cars to coast freely. I have a 2004 LS430......I did get the software upgrade done on my car to prevent the low speed shifting issue that these cars are known for....the new software did solve that problem. But not only is my car downshifting on the down hill grade it also jumps my RPMS up substantially when it does this. Of course gas mileage suffers a bit when this occurs as well. The only way to keep her from downshifting is to keep the pedal down.....but who pushes the pedal down going down hill? Dont answer that

I guess I can have the dealer drop in a different software version.....not sure what else to do.....I am hoping this is just normal for our cars.

Fixman

It's when going down hill the gear automatically selects a lower gear like forom 6th to 5th or 4th. It's like down shifting on a manual gear.
If I am correct, this started withe the 6 speed (2004 model LS) I don't think you can override it in drive but you can always go manual and chose what ever gear you like.

Lavrishevo

iTrader: (1)

There was a certain section of my commute home that my LS use to downshift. It would only downshift after hitting the brakes though. Your car should not downshift if you are off the brakes.

jpv7774

Two interesting answers........I never thought about the manual shift idea...I have always thought that might be a weak link and that the technology was new back in 04 for electronic shifting. Also I just like to cruise....not really interested in shifting the big girl...but that would certainly solve the issue. Yes my car is an 04 and it did even have the transmission replaced back when it was new due to the recall. Mine is the 6 speed tranny......maybe the 5 speed didnt do this.

Lavrishevo......good to hear from you....I thought u were off the site. I havent spent much time here lately myself. Your car as I recall is an 04 as well but a Ultra Lux......I would assume same engine and tranny. Interesting what u say about tapping the brakes....I will consciously not touch the brakes on the down hill and see if she will let go. I mean I was watching the tach on a down hill the other day and during its auto downshift she revved up to 3k.....thats not cool. She shifts smooth as butter and is running great......if I had to guess I think the new computer software update I had done is the root cause of this issue. Again for others who will read this...I had the software updated due to the low speed coast then rev and lurch shift issue that our cars are known for..............Lav u didnt have the software done on your car did you?

LSGarry

Both of my cars do the same thing and as "Lav" indicated, it will only downshift if I touch the brakes. I believe its programmed to do this and I actually will use this feature if I find the car is "coasting" too fast and need to slow it down by tapping the brakes. I also don't believe you are using more gas when this occurs as only the throttle will allow more gas to be used.

tallcaguy

Not much experience w/ the 6 yet. When I coast to a light, the car doesn't automatically downshift. It did take some practice to get the manual downshifts right. Just like any manual transmission, downshifting too early gets sudden high rev's and some body movement (the car, not mine). With the 6, there seems to be a slight pause upshifting to keep things smooth. No pause when downshifting tho (that I can detect). With 2 (recent) drain and fills and the TSB flash, auto shifts are silky (not quite as good as the 5 speed but very close).

daddykay24

JP, the engine braking is normal. I prefer it to riding the brakes down a hill.

jpv7774

Thanks for the replies all.....I like the engine braking on steep hills but it also seems to brake on slighter down hill grades. I just wish I could dial it in to exactly how I prefer but surely that is not gunna happen. I love the car...but thats the only thing I would change to my silky smooth ride.

DavidinCT

Can this be disabled via Techstream ?

fensterlip

I'm wondering if this compression load to hold the speed down on a long downhill wasn't designed into the engine and transmission spec's as to not put an undue load on the drivetrain. Said another way, I can't imagine the Toyota engineers designed a downshift feature that put an excessive load on the system. If the brakes get hot a lot if not most brake pads lose some of their effectiveness. This would mitigate that a bit.

airchomper

Engine braking is still used by people who tow things and motorcyclists. Heck, semi-trucks and some diesel pickup trucks have special systems to enable engine braking on diesels.

The engine actually cools down while engine braking because the cars cut the fuel in engine braking conditions ( 0 throttle and engine speed higher than idle). If you were to put the car in neutral, the engine would run its idle program. What do you think is going to make the engine warmer, 2000 RPM (so the water pump is really spinning fast) and no fuel, or 800-ish rpm and idle?

The only way to cut engine braking is to put the car into neutral. When it's in neutral, the transmission and torque converter don't recirculate fluid as much and can overheat very, very quickly.

Additionally, riding the brakes is a really good way to boil the fluid. I think our cars spec DOT3 brake fluid which has a boiling point between 300-400 degrees (depending on 'wetness'). It's not too hard for a 4000 lb car to boil its brakes and get some fade. I've heard people say that they start to experience fade after 6 quick stops from 60 mph to 0 - something that transfers ~ 6 x 10^6 joules - or the same amount of energy transfer as using your brakes absorb all the energy of descending about 200 meters / 600 feet. Obviously, no road is completely vertical and it takes a lot longer than 600 feet traveled to change your height by 600 feet, but it should give you context for why people care to preserve modern, disk brakes (even those are over-speced as the ones on our cars).

But consider the 'conservation of energy' (I know this doesn't back entirely into the conservation of energy and it's not a frictionless system but there is a symetry that exists) argument - at the end of the day, it doesn't really matter to your driveshaft, or transmission, or axles whether they're passing negative or positive torque (as measured at the crankshaft). If you maintain 75 mph on a 6% grade, you're pushing a lot of power through the car for an extended period of time and no one would worry about overheating an LS in good repair. Why is it any different to the running gear (non-engine) if you're absorbing a lot of power into the engine?

You're right about the engine exposing itself to more of a vacuum - but these cars don't have piston ring issues so it's unlikely that they'll consume too much of their oil, and the vacuum can't be that high - It's not a perfectly sealed system. Most cars have 3 piston rings - the top two seal the combustion chamber and the bottom one controls the oil. Racing motorcycles have one or two. Take a Suzuki RMZ-250 with a Yoshimura piston, a bike that has 1 piston ring, spin the engine up to 13,200 rpm and snap the throttle closed. I'd eat my shoe if more than .01 ml of oil were burned in the whole time it takes for the engine to drop back to idle. The idea that our cars are going to get enough oil to foul the plugs or make serious deposits in the combustion chamber (with the relatively thick oil fighting past 3 sets of piston rings against an bore with some really sophisticated linings). The rings seal the engine pretty good during combustion events - even without considering the impact of the fuel, 10.5:1 compression means our engines are squishing air to about 140-155 psi. There's no way our engines can support negative vacuum, we're probably just below atmospheric pressure. I'd be surprised if any of our engines saw much beyond 12 psi below atmosphere. Do you think it's reasonable to say that piston rings that can withstand at least 150 psi of positive pressure would struggle with a vacuum of 12 psi?


Worrying about oil deposits on the spark plugs because of engine braking is like worrying about wearing out the steering rack / inner tie rods when your car is on a lift and a technician is moving the front wheels to get easier access to the brake pads. There's probably something happening at the margin but compared to the typical use cycle it's nothing.

toddmorr

agree with airchomper's comments.....any extra wear on these engines via engine braking has to be lower than trivial...really. Even at 3000 rpm which i've seen occasionally i just can't see it being any issue at all.

Fixman

As abouve. Plus if I have to chose between the hole vehicle waring down or safety. I chose safety, as I don't want my brakes to fade when I am going down hill and I find something blocking the lane around a the corner.
Use engine brake it's a safety issue, mony comes and go. You only have 1 life.

Fixman

"Worrying about oil deposits on the spark plugs because of engine braking is like worrying about wearing out the steering rack / inner tie rods when your car is on a lift and a technician is moving the front wheels to get easier access to the brake pads. There's probably something happening at the margin but compared to the typical use cycle it's nothing."

haha this reminded me of the wear sunscreen.
Don't worry about the future or worry that know that worrying
Is as affective as trying to solve an algebra equation
By chewing bubble gum
The real troubles in your life are apt to be things
That never crossed your worried mind
The kind that blindsides you at 4 p.m. on some idle Tuesday

Read more: Baz Luhrmann - Everybody's Free (to Wear Sunscreen) Lyrics MetroLyrics

monrovea

My car down shifts on a hill, but only after tapping the brake. The dealer also confirmed this is what happens. I don't think your car will down shift UNLESS you hit the brake.