S Mode & ECT Use for Mountain Driving

I tried it today for the 1st time. Went downhill in S4. Didn’t notice any real difference as far as engine breaking. My RPMs were around 2K or a little higher, speed was around 45 but got up to 50 before I had to hit the brake. I still had to brake multiple times to slow down on the descent, especially through the switchbacks. I didn’t notice a ton of engine braking. Most of the time though I had my foot off the pedal, just braked occasionally as the truck kept gaining speed. What am I missing? I feel like leaving it in D would’ve been similar. Do I need to do S3 next time?

 

you should be in S3 at that speed. S4 is too high if you are only pushing 2k rpms

 

I thought when you put it in S4 that just meant it was the highest it’d go. But the display showed S4 the whole time. Next time downshift? So was it bad driving it in S4 at those RPMs?

 

This is an item of thought for me as well.

Typically when just towing my little camper here or there without and gear in the bed or the camper I just use ECT
around town on flat surfaces and limited freeway driving.

When the truck bed has camping gear, coolers, the works I use ECT and slip to S4.
Should I be slipping to S5 or just use ECT. Or is ECT and S4 the best starting point.
Or should I fogettaboutit and just use S4 or S5.

Seems I remember having to drop so S3 on steep inclines on some occasions.

Camper only weight about 1,000 pounds or so - might be 1,200 tops with stuff in it.

 

It wasn’t bad at all, you just need to be in a lower gear with a higher RPM to get any effective engine braking. You could go down the hill in S2 if you really wanted to stay off the brakes.

 

Towing little campers has different rules for a different reason.

90% of the time I put ECT on, S4 and forget about it. The reason being is that frequent shifting in and out of the two overdrive gears (5 and 6) when towing can generate a lot of heat and is generally harsh on the transmission.

If it's a long flat stretch above 60mph I'll sometimes bump it up to S5 and gain about 2 mpg from the higher gear. But I also watch it to make sure it can hold 5th (at 65 mph 5 is under 2k rpm, 4 is around 3k). If its frequently hunting between 4 and 5 like it would in wind or rolling hills, knock it back down to 4 and leave it.

You won't hurt it in S4 even driving all day on the interstate. The only reason to bump up to 5 (if the truck can hold it) is for fuel savings.

 

Excellent description thanks.

 

Oh ok. Does the engine braking stop you at a certain speed once you set it or does the gravity/steepness make it so it usually exceeds it anyway? What’s typical speed for S2 and S3? I was in S4 and had people on my a$$ that were flying down the mountain. I would be a little hesitant to be at S2 if it keeps me at like 30mph. Would like to be 40/45mph. When I put it in S4, I thought that doesn’t mean it STARTS in S4, I thought it just means it won’t go higher than selected - but mine showed 4 the whole time. So if I was going about 50 down the hill and hit the minus - it would smoothly slow me to S3? Or should I brake to a lower speed before doing that?

 

There are no set speeds for a gear, you just need to experiment and see what works for you in each situation. If 4th gear isn’t providing the braking you want then down shift to 3rd and see how that goes. If that’s still not enough you might be able to downshift to 2nd depending on how fast you’re going and what the engine RPMs are sitting at. There’s no definitive answer, on a shallower angle or shorter distance hill S4 might be fine while longer/steeper hills might need S3 to maintain the same speed without using the brake pedal.

 

So if I put it in S4 and change to S3 going down the mountain, if speed picks up it won’t auto change back to S4? Bc I thought it auto shifts up on its own? Or once you change it, it stays at whatever you changed it to and then you manually have to shift it back up? Asking bc I thought I watched a YouTube video where it auto shifted on its own up to S4. I’ll have to play with it again. Like once I’m at the bottom of the hill, at what point would I shift it back up to S4? Or could I just kick it right over to D at that point?

 

Have you ever driven a manual transmission vehicle? I’m guessing no based on your understanding of gears but if you have then just shift the auto as if it were a manual. Downshift for more braking downhill or more power uphill. Upshift if you need a higher speed or are reaching the RPM limit of the gear you’re in. On flat ground put in in S4/S5/D depending on how much weight you’re towing and how much the transmission hunting around between 4th and 6th annoys you.

 

The video showed it upshifting from 1st to 4th gear because the gear selector was set at S4. If you select S3 (from S4) the transmission will downshift to 3rd gear and won’t upshift to 4th gear because you’ve limited the top gear to 3rd. When you determine that you don’t need the engine braking provided by S3 you can manually upshift to S4, or kick it over to D and the transmission will take over gear selection for your situation.

 

Ok - & I def couldn’t have done harm coasting down the mountain in S4 the whole time? I’ll try S3 next time. Do I need to take my foot off the accelerator whenever I downshift or upshift?

 

Careful doing that. I uses cruise on a long descent once and realized it was braking the whole time when traffic came to a sudden slow down and I tried pressing the brakes and realized my brakes had significantly lost their strength. I wouldn't recommend doing that after said experience. I wish they would have something in the guage cluster light up letting me know cruise control is using the brakes.

 

S4 no harm. If you’re pressing the skinny pedal and select a higher S gear at the same time, the trans may not upshift right away. The trans still decides at what point it’s going to do the upshift. If you want to use a downshift in S mode to take advantage of engine braking to slow down then instinctively you’d probably take your foot off the gas. But there’s no harm done if you don’t. After a few times playing around you’ll do what’s comfortable for your situation.

As you probably know by now, the S mode does not operate like a manual transmission. It simply limits the top gear your trans can achieve on the upshift and provides a way to engine brake if you manually downshift.

 

Skinny pedal? I just have the gas and brake pedal. It’s an automatic.

I’m still confused on if it will automatically downshift on its own or not. Like when you move it over and it defaults to S4, if you brake and slow your speed significantly, does it drop to 3, 2 or 1 on its own? And if so - does the display reflect it or will the display always just show the limit you set it to (default of 4)?

 

Skinny=gas pedal.

When in S4 the trans will shift up and down as if in D (with 4th the top gear) unless you intervene by selecting a lower or higher gear manually.

if you’re driving along in D and you select S mode, the display will show 4. If you were in a higher gear in D (like 5 or 6) it will downshift to 4th gear. If you were in 3rd or a lower gear in D, it will remain in that lower gear until the trans decides it should upshift but still display 4. The display only shows the top gear limit when in S mode.

S4 mode acts like D with only 4 gears.

 

Ok great. So no need to downshift further when coming to a stop, it’ll do it all for me. Do I need to be at a particular speed when flipping it from S 3 or S 4 back over to D? I’d imagine you wouldn’t want to do that going like 20 or so.

 

When you push it back over to D, the trans knows what gear it’s in and D takes it from there. After all, it’s ‘automatic’

 

I have not. So I prob shouldn’t even have attempted this bc I understand it so poorly. I put it in S4 going down a steep hill with lots of switchbacks - far from Flat Ground like you recommended. Hopefully that didn’t do any harm. It doesn’t sound like it did based on other comments - but it def wasn’t the correct gear to use so I’m still a little worried. But what’s done is done. I’ll use S3 next time - or maybe just leave it in D to see if it auto engine brakes at all like some newer cars do anyway.