[TheFrankenberry]

Okay, I've always driven where if I'm going down a long hill, I put the tranny into Neutral and just coast down. Why feather the gas when you can coast and not touch the gas pedal at all? I did this a ton while growing up in hilly Pittsburgh and traveling about the Appalachians. Now I'm in Hawaii where I can coast downhill for up to 5 minutes at a time!

I've made my daily commute, in my new 2010 R/T w/ MDS auto, over 50 times now. This is the second time this transmission lock-up event has occured...

I'm coasting down for a good three minutes in Neutral, the highway levels out and I eventually put it back into drive. I step on the gas and NOTHING. The transmission stays locked in 5th and around 2000rpm with an achingly slow drop in my speed. I push the accelerator and it's apparently not talking to the engine because I don't hear my Lil' Hemi roaring or seeing the tach or speedo positively moving. I have to put on my hazards, pull off to the side of the highway, stop, put my R/T in park, and finally back into Drive--where it resumes normal operation. (Well, besides the tach needle doing a slight up and down jiggle when cruising at a constant RPM for the next 15 minutes or so.)

I called my dealer's service department and was told, "these new auto CVT transmissions just can't be popped into neutral like manuals or older autos; you can't just coast in Neutral with them".

- Is this what's happening?
- Why exactly does it lock up the tranny?
- Why would it only happened in 2 out of 50+ downhill coasts?

 

[DBDLIVES]

When you put these cars into neutral while driving, MOST of the time they will go into LIMP IN MODE. Its totally normal. My Charger did it and both my new Challengers do it. Also, these cars do not have a CVT trans in them. The dealer might wanna brush up on what these cars have. LOL

 

[homerzeppelin]

When you put these cars into neutral while driving, MOST of the time they will go into LIMP IN MODE. Its totally normal. My Charger did it and both my new Challengers do it. Also, these cars do not have a CVT trans in them. The dealer might wanna brush up on what these cars have. LOL

LOL +1 NO CTV in these vehicles.

 

[TexasMoJo]

Still didn't find out..... WHY

 

[CURT LF]

Still didn't find out..... WHY

Sensor input data outside of programmed parameters or indicating failure = limp mode.

 

[R/T_6Speed]

My guess (and guess it is) would be the computer isn't liking something its seeing during the coast and putting the car into limp mode. I don't think it hurts an automatic to do that but certainly the computer probably wasn't designed to deal with long coasts in neutral.

CVT transmission... lol. I'm amazed at dealers that don't have a clue but talk with authority. I was talking to a Dodge salesman last week about Challengers when I mentioned the new 392 to which he said, "oh, that program was canceled and they didn't actually make any". All righty then.

 

[Tinstar]

Ha, two months ago I told a service manager that I was hoping to see a 392 very soon. He replied "We have serviced one recently." The salesmanager when asked if they are getting one in "said I don't know anything about them: duh

 

[caj]

I've always heard that it is not a good idea to put your auto tranny in neutral and coast. Maybe some of the technicians/mechanics can chime in here.

 

[TheFrankenberry]

So what exactly is Limp Mode. From what I understood it just limited your speed and higher gears, not lock it in 5th at 2000rpm until you bring it to a dead stop and put it in Park...

 

[70stroker]

Coasting downhill in 5th gear overdrive under no real load should have your engine barely at an idle. Why bump it out of Drive if the RPM difference is not saving you anything?
Tell us what you are seeing both in Drive and in Neutral for RPM's. I can't help but think it is less than 100 RPM's.

 

[DragCad Racing]

Another reason you should keep the car in gear going down hills is that the Challenger autos have hill ascent and descent assist. The auto will downshift a gear when you are cruising up a hill or coasting (foot off gas) down a hill. It's more subtle than downshifting a gear using autostick, but the car does try to help. It doesn't just go into top gear when you coast down hills like older autos. Hawaii has more than a few hills to deal with, you should let your car help you. Leaving the car in gear is safer, the transmission can help slow you down.

 

[homerzeppelin]

Another reason you should keep the car in gear going down hills is that the Challenger autos have hill ascent and descent assist. The auto will downshift a gear when you are cruising up a hill or coasting (foot off gas) down a hill. It's more subtle than downshifting a gear using autostick, but the car does try to help. It doesn't just go into top gear when you coast down hills like older autos. Hawaii has more than a few hills to deal with, you should let your car help you. Leaving the car in gear is safer, the transmission can help slow you down.

I think he wants to avoid the car slowing him down as his goal would be to save gas.

The car is telling him not to do it though.

 

[DBDLIVES]

Even though its coasting in drive it still saves gas. During coast down it cuts fuel.

 

[randycat99]

I agree with keeping it in gear while coasting down a hill. If you have a ScanGauge monitor (or similar product), you'll find that on a big grade it is pulling 100+ mpg, if you keep it in gear (if not already in fuel shutoff mode). I don't think you need to worry about fuel consumption down a hill. 50-ish mpg is not all that unusual on a shorter, smaller hill, as well.

Where I'm living now, the entire town exists on a loooooong, imperceptibly mild grade. When I head on a long road in the direction down the grade, I can literally pull 30 mpg on the whole trip, even though I am still "city driving". I'm literally doing a controlled-coast (mild engine assist) for minutes of duration.

 

[STONEWHITE R/T]

Limp in Mode limits the car transmission to second gear- from my experiance. What your doing is introducing a higher transmission output speed than what is being put in at an Idle speed - RPM. (Coasting). The computer isn't thinking that. It is saying to itself. I am at idleing RPM - input speed sensor, vs. Output shaft speed sensor - seeing high RPMs. The out put is out of range vs what is going in. Driveshaft vs. Engine. The computer needs to think and straighten itself back out. Remember it reads throttle inputs also.
Keep it in drive . Like the above poster wrote - on DECEL. the injectors shut OFF until the vehicle comes to a certain speed and then turn back on. So you are not saving anything but more than likely damaging your transmission by little to none fluid flow internally while in Nuetral @ Idle speed and moving fast. That is why you do not Tow and Automatic.

FWIW - I travel home down a long hill on I-35 here in Texas. My 96' Ram was a stick. I could get up to about 70 MPH at the top of the hill and let it coast all the way down in 5th gear. Keeping the throttle closed I could begin to watch the temperature guage drop by the bottom of the hill by letting the high vacuum make such a low pressure area in the intake it would actually bring the engine temp down. Not a lot but noticeable on the guage. Worked every time.

 

[TheFrankenberry]

Coasting downhill in 5th gear overdrive under no real load should have your engine barely at an idle. Why bump it out of Drive if the RPM difference is not saving you anything?
Tell us what you are seeing both in Drive and in Neutral for RPM's. I can't help but think it is less than 100 RPM's.

When coasting downhill in neutral it's 750rpm.
When coasting downhill in Drive at 55mph it's at 1600rpm and 65mph at 2000rpm.
Also, coasting in neutral has the car wanting to go 75+mph if I let her whereas when coasting in drive it won't hold the speed but gradually drop until I apply some throttle.

 

[randycat99]

Think about it this way, coasting downhill in gear, it is probably using even less gas than if it was in neutral, regardless of the difference in rpm. The energy of the car motion is going toward spinning the engine (which is why you are slowing down or just holding at some threshold speed), instead of using gas to keep it spinning at idle. At best, it is using exactly the same fuel, so there is really no advantage to free-rolling it, as opposed to normal in-gear operation.

Even if you apply light throttle to hold at a higher speed down a long hill, you'll still be pulling 35-50 mpg (or more) over that stretch, so it's not like there is much to complain about as far as fuel use.

 

[Redliner]

I disagree with some of this. I read a big article one time about "Hyper-miling" and it is a big time deal all over the country. It involves alot of shifting to neutral down long grades and I goofed around with it on my 95 T-100 truck. My idle went from 1500 to about 700 and the car (truck) would pick up a lot more speed and inertia by coasting rather than having to turn the engine. I have a great big hill just before getting home every day from work. I tried the neutral thing in the Challenger once. Just once. It did the same thing being talked about here. The computer doesn't like it at all. I will never try it again. Sure works in the old truck though! And the Hyper-milers swear by it.

 

[randycat99]

I'd suspect that a lot of that hyper-miling hijinx is really directed at manuals, rather than autos, in order to yield anything useful. On a manual, roadspeed is directly coupled to rpm for a given gear, so you either you have a good match-up to achieve what you are wanting to do, or it doesn't match-up, and you elect to pop it into neutral to decouple that direct relationship.

This is far less an issue when it comes to automatics, barring extreme speed or odd gear selection scenarios. The coupling is indirect, hence there is a good deal of leeway to accommodate road speed vs rpm in a near-free coasting state. It allows just enough differential such that engine speed gets a mechanical-assist from the drivetrain (such that minimal gas is used to do the same as if the engine was just idling at neutral) w/o outright limiting how much road speed can be achieved downhill.

 

[Redliner]

Yes. The hydro-link of automatics does help with that. Definitely de-coupling a manual from the transmission by engaging the clutch or even shifting to neutral does the trick. My T-100 is an automatic and when I go down that big hill on the way home, my rpm's drop to lest than half. I'm just goofing around because the truck gets 21mpg anyway but I can see the unloading of the system before my very eyes. Just doesn't work at all with the Challenger.