2017 Miramar-Tow Haul Mode

Grumpy Grampa

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Hi. I have a 2017 Thor Miramar 37.1 with a V10 engine. When I drive I always use tow haul , even if I am not towing my 2023 Jeep Grand Cherokee. My question when going down step grades, and the tow haul mode is working slowly the coach down, if I want to disengage the tow haul mode sooner while it’s working is it safe just to turn it off, or should I let the system work through the process, for I can speed up again?

Thoughts

Thank you
 
Why? Would you want to turn it off?

But to answer your question - you can turn it on and off at any time while driving. I usually leave mine off unless coming to a stop or going down a steep grade.
 
I often drive with my finger on the button in "rolling" mountain areas. I push the button to turn on tow/haul when going up a long steep incline. I tap the brakes to select the gear I want on the descent. However, it often "hangs" in low gear longer than I like at the bottom. So I just tap the button to disengage tow/haul... which gives me an immediate upshift.

It's similar to driving an older automatic tranny and using low-1 or low-2 to prevent/control shifts. That's probably where engineers got the idea for "tow/haul".
 
I often tap the button to disengage tow/haul when I'm at or very near the bottom of a descent when the road ahead permits to allow the transmission to smoothly up-shift and then push it again to re-engage tow/haul.

I find that the computer unnecessarily hold onto the lower gear too long and causes the engine to require more throttle to up-shift otherwise. Besides that, I just leave it engaged all the time.

You'll develop your own habits and processes for whatever works best for you. The above works for me.
 
My gas pedal seems to override it.
5200rpm is the most I've hit while it was holding a downhill speed.
I love this tow haul thing.
 
I leave it on all the time. Most of my driving is east of the Rocky Mountains, mainly in the Central Plains. Since the computer can not see the road ahead it relies on it's programming. When the road ahead it suitable for a higher gear and the computer is holding in a lower gear, I just ignore it and let the program do it's thing. I figure the RV doesn't have the momentum the computer thinks it needs for a higher gear. When the momentum is achieved it will upshift.
 
Why? Would you want to turn it off?

But to answer your question - you can turn it on and off at any time while driving. I usually leave mine off unless coming to a stop or going down a steep grade.

I use my tow haul a lot on grades as well. But I have often wondered about the way my Miramar V10 gasser seems to auto downshift to lower gears when on downhill runs WITHOUT tow/haul engaged. While that might be helpful at times I dislike when it drops several gears bringing engine rpm's up above 4000. I hate the roar - I would rather have it one gear higher to provide some engine braking but then to just tap the brakes occasionally to keep speed under control. Anyone know a way to control this behavior? I have been known to shift to neutral briefly and allow engine rpms to drop before shifting back into gear.
 
The only time I've noticed our ACE (F53 chassis w/V10 gas engine) downshift on a downgrade when not in Tow/Haul mode is when the cruise control is on.
 
The only time I've noticed our ACE (F53 chassis w/V10 gas engine) downshift on a downgrade when not in Tow/Haul mode is when the cruise control is on.

Yeah I wish that were true wit my Miramar, but it definitely will do it regardless of cruise control... I know that because I often tap the brakes briefly and repeatedly until it brings the engine RPMS down to a reasonable level. But invariably it will speed back up again quite often on a long downhill bringing the RPM's up above 4000. Obviously that would kill cruise control, and if I slow down quite a bit, drop it into neutral for a few seconds and then back into drive it will start downshifting again as the rig picks up speed/
 
ok thank you... I was wondering if there was a trans mission problem. I will take it to the local Ford Trucks dealer and repair center in north portland this winter. thanks a lot
 
I wouldn't be so sure about it being a transmission problem, at least without additional data.

My suggestion would be to set up a dashboard on one of the OBDII apps (I use Torque Pro since I've had it a while) and monitor to see what the PCM is commanding the transmission to do. If the downshifting is being commanded by the PCM, then the transmission is only doing what it's being commanded to do. If it downshifts without a corresponding command from the PCM, then the transmission has some sort of issue.

I'd also monitor the PCM's status for the TOW/HAUL switch. It may be have the mode engaged without your knowing or intending it.
 
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I wouldn't be so sure about it being a transmission problem, at least without additional data.

My suggestion would be to set up a dashboard on one of the OBDII apps (I use Torque Pro since I've had it a while) and monitor to see what the PCM is commanding the transmission to do. If the downshifting is being commanded by the PCM, then the transmission is only doing what it's being commanded to do. If it downshifts without a corresponding command from the PCM, then the transmission has some sort of issue.

I'd also monitor the PCM's status for the TOW/HAUL switch. It may be have the mode engaged without your knowing or intending it.

Good morning... this seems like a very knowledgeable analysis of the problem. With my longtime (60 yr), albeit limited, knowledge of automotive engines and transmissions, I seriously doubt this is a transmission problem since the tranny functions perfectly in every other way, driving thousands of miles over the course of weeks on end on some of our more recent trips. The rig only has about 21,000 miles on it and drives like new... and btw this behavior has been present ever since the rig was new. I just have tolerated it and never done anything about it because it is difficult to find a qualified tech in a place where this behavior can be demonstrated.

Your suggestion that "the downshifting is being commanded by the PCM" makes a lot of sense, whether that might be some internal command or it may well be that PCM may be engaging the TOW/HAUL switch surreptitiously without some visible status indicator. I can tell you that if this *is* the issue, it is definitely not lighting up the dash indicator which always shows up when intentionally engaging the TOW/HAUL switch which I do use sometimes, but not always since the same kind of downshifting occurs whether switching it on or not. And it always has. So that lends some credence that the TOW/HAUL switch is being commanded by the PCM without my intentionally turning it on. It may be worth noting that the tranny will drop to a lower gear on its own whether in "D" (drive mode) or manually dropping it one gear. Whereas I would be happy to have it use engine braking in 5th or 4th gear (I think it would be), it will still drop down further into 3rd just like the TOW/HAUL mode would have it do). And when it does this, I fell obligated to tap the brakes occasionally anyway to keep the engine RPMs in a moderate range (say below 4000) both for noise mitigation as well as engine wear and tear.

I presume "PCM" stands for "Power Control Module" or something to that effect? When you refer to "one of the OBDII apps" could you make a specific recommendation?? If I can make a valid diagnosis it may help me guide the repair center directly to what needs to be done, since I don't have the expertise to make such adjustments or repairs on my own, I'm pretty sure. The factory repair center in the Portland area is Northside Ford and that part of town is pretty level. To demonstrate the issue to a technician we would need to drive up towards Mt Hood and turn around and head back down to encounter the kind of grade needed to evoke this kind of behavior. It is never a problem driving around in more level areas... it only occurs on steep downward grades and it's going to be very difficult to have a tech onboard for the length of time it would take to demonstrate the behavior. Hence some detail from an OBDII app done on my own time might help the tech effect an adjustment or repair.

I'm going to describe one other anomaly which may or may not be related. The speedometer on this rig has never corresponded directly to actual speed. When my GPS says I am doing 65mph, the speedo with read about 74... like wise when it reads 65 I am only doing about 56 or 57. I have always thought the speedo was simply never calibrated for the tire size properly and that's all there is to it, but now I wonder if maybe it might be related to the automatic downshifting as well?

Again, thanks for the indepth suggestions and any followup you can provide and then I'll take it from there, although probably not this time of year. It would need to wait until spring now.
 
Whether it's caused by the transmission itself, or controls external to the transmission, it is still a transmission problem. That's where the trouble symptom manifests itself. And in the case of a coasting transmission suddenly downshifting to cause the engine to rev up without known influence by the TOW/HAUL input or Cruise Control input, it is abnormal for the transmission to do that. So could this transmission problem be caused by a failing control module? Absolutely, but let the expert figure that out. Your job is to accurately describe the symptoms starting with: "My transmission seems to auto downshift to lower gears when on downhill runs WITHOUT tow/haul engaged."
 
... it's going to be very difficult to have a tech onboard for the length of time it would take to demonstrate the behavior.

Maybe a video showing when it occurs?

I'm going to describe one other anomaly which may or may not be related. The speedometer on this rig has never corresponded directly to actual speed.

Hmm, channeling Click & Clack (unencumbered by the thought process...) it would seem possible the computer is also getting this anomalous speed signal. And if so would it then tell the transmission to downshift to prevent overspeeding?
 
Whether it's caused by the transmission itself, or controls external to the transmission, it is still a transmission problem. ..... Your job is to accurately describe the symptoms starting with: "My transmission seems to auto downshift to lower gears when on downhill runs WITHOUT tow/haul engaged."

Yeah point well taken, although if the suggestion from PS89, Retired electronics tech, about getting a reading thru the OBDII port to see what the PCM is commanding the transmission to do, might help the tech figure out how to fix it without actually seeing it in action. As long as the OBDI app and cable is not too expensive. Maybe PS89 could post a link to a good but inexpensive one? And the other suggestion to perhaps take video when it downshifts on a downgrade might be a great way to show them what it is doing. Thanks guys.
 
The advantage of having your own OBD reader might be that often the system only saves the 'codes' for a limited time. If so, by the time you take it to a shop it may have been operating normally long enough that it will have erased the code.
 

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