Tow Haul button does nothing

[Rand Kibodeaux]

I have a 2108 2500 6.7L and 68RFE transmission. So far it has 5,000 miles on it. I cannot see any difference in performance when in tow/haul mode. I have tried numerous tests while hauling my 4,000 lb travel trailer and I cannot find any scenario in which using the tow/haul mode makes any difference. The dealership says the transmission is working as it should according to their computer readouts, but I think they are giving me the brush off. The truck does not shift any different, while towing, under any condition (uphill, hard acceleration, easy acceleration, downhill, level towing, various speeds, shift point rpms) whether in or out of tow mode. Another thing that leaves me very suspicious is that a friend of mine with the exact same truck gets 14-15 mpg on the same highways as I drive while I average only 10-11 mpg. His travel trailer weighs more than 8,000 lbs. Any suggestions?

 

[jhenderson]

Does the exhaust brake behave in a more aggressive manner in tow/haul? The converter should stay locked and the exhaust brake should stay active while automatically downshifting all the way to second gear while the trailer is attached.
As for mileage? I’d be hard pressed to believe what your friend is reporting while towing 8K.

 

[WalterJ]

I

Does the exhaust brake behave in a more aggressive manner in tow/haul? The converter should stay locked and the exhaust brake should stay active while automatically downshifting all the way to second gear while the trailer is attached.
As for mileage? I’d be hard pressed to believe what your friend is reporting while towing 8K.

I can believe that highway mileage, IF he keeps his foot out of it & cruises at 60MPH. Afterall, it's only 8K#.

 

[sag2]

We just returned from the Cummins event, 7,600 miles towing a 5700 lb Lance and we averaged 11.61 for the entire trip. That was at 70-72 with the cruise on almost the entire way. Have a little over 15,000 miles on the truck when we got back.

 

[WalterJ]

We just returned from the Cummins event, 7,600 miles towing a 5700 lb Lance and we averaged 11.61 for the entire trip. That was at 70-72 with the cruise on almost the entire way. Have a little over 15,000 miles on the truck when we got back.

IMHO - not bad at all. Speed kills; Mileage too. Our measured mpg on various highway trips is directly correlated to MPH; 9mpg @ 70+mph & 12mpg @ 58-60mph. It's tough to make accurate comparisons due to the variables of wind, terrain, temperature, etc., but when I realized how difficult it is to stop our 22K# rig (don't ask), I got more & more comfortable cruising @ 60mph.

 

[Cummins12V98]

Drive 25 mph with TH off, turn it on does it drop a gear? Try 30, 35 and so on.

Report back.

 

[Rand Kibodeaux]

Drive 25 mph with TH off, turn it on does it drop a gear? Try 30, 35 and so on.

Report back.

Under no condition or circumstance will the transmission drop a gear by switching to tow/haul mode. I’ve tried every scenario I’m able to imagine. I’ve tried it 7% grades, level ground, every speed from 30 to 70, in fourth, fifth and sixth gears, from a dead stop, even pulling over and turning the engine off and re-engaging the tow button upon starting. Nothing seems to make any difference at all.

 

[mpaulson]

The easiest test is to get up to hiway speed (where its safe to play) and let off the throttle, tap the service brake and see how it slows down. With the tow/haul OFF and with the Exhaust brake on, the exhaust brake should come on, but the transmission will not continue to downshift to lower gears. Do the same thing, get up to hiway speed with the Tow/haul on, and the exhaust brake on in the "FULL BRAKE" mode (orange symbol) then tap the service brake lightly, and the exhaust brake should come on and then slow you down and as it slows down the transmission should start down shifting through the gears. If it doesn't downshift on it's own, there's issues, and find a better dealer.

 

[SnoKing]

Drive 25 mph with TH off, turn it on does it drop a gear? Try 30, 35 and so on.

Report back.

I better test is push the gear selector to show 6 gear as the highest gear and then slowly speed up and record the speed that each shift occurs without TH on and repeat it with TH on. My Aisin will not shift to 5th gear until over 55 with TH and 6th gear until 65 with TH. Shifts much sooner without TH. Similar for lower gears also.

 

[SnoKing]

Another thing that leaves me very suspicious is that a friend of mine with the exact same truck gets 14-15 mpg on the same highways as I drive while I average only 10-11 mpg. His travel trailer weighs more than 8,000 lbs. Any suggestions?

Like the size of a fish caught, some people stretch the truth on MPG. Until you both fuel at the same time/same pump and drive the route at the same time and refuel(again same pump) and hand calculate your mileages you do not know for sure that he is getting better mileage.

 

[SnoKing]

Under no condition or circumstance will the transmission drop a gear by switching to tow/haul mode. I’ve tried every scenario I’m able to imagine. I’ve tried it 7% grades, level ground, every speed from 30 to 70, in fourth, fifth and sixth gears, from a dead stop, even pulling over and turning the engine off and re-engaging the tow button upon starting. Nothing seems to make any difference at all.

If you drive 60 MPH without tow haul flat level highway, the indicator will show 6th when you first select it with the down button. You might have to push it twice. Now select Tow Haul and it should shift to 5th gear and indicate if your trim/option level has the EVIC readout of gears. RPM change will indicate shift also. If NOT then you need a different dealer like someone else suggested.

 

[Cummins2014]

Easy test ,40 mph it stays in 4th with tow haul ,if not its in 5th.

 

[CoastyAV8R]

better test is push the gear selector to show 6 gear as the highest gear and then slowly speed up and record the speed that each shift occurs without TH on and repeat it with TH on. My Aisin will not shift to 5th gear until over 55 with TH and 6th gear until 65 with TH. Shifts much sooner without TH. Similar for lower gears also.

To me this is the most noticeable difference between the two tow haul modes. It also won't shift as casually with the TH on, meaning it shifts at a noticeably higher RPM than with it off.

 

[Cummins2014]

To me this is the most noticeable difference between the two tow haul modes. It also won't shift as casually with the TH on, meaning it shifts at a noticeably higher RPM than with it off. It's important if you take someone from the dealer's service dept on a test drive to show them the issue that they have some experience with the Aisin or these differences will be lost on most of them.

We seem to be making this a little bit more scientific then needed, its pretty simple it holds the gears longer in TH. Easy test, he has a 68rfe , as said 40 mph it holds 4th in TH, if not it shifts to 5th. What else is there ?. If it is not holding the gears at certain speeds on a flat road in TH , then he's got a problem .

 

[AH64ID]

Does dash show tow/haul active or only the button?

 

[Cummins12V98]

I better test is push the gear selector to show 6 gear as the highest gear and then slowly speed up and record the speed that each shift occurs without TH on and repeat it with TH on. My Aisin will not shift to 5th gear until over 55 with TH and 6th gear until 65 with TH. Shifts much sooner without TH. Similar for lower gears also.

With my 68RFE I would always be in the next gear when tH was not on, turn it on and wala the trans dropped a gear. same goes for the AISIN.

Rand, you have a problem!

 

[Cummins12V98]

Like the size of a fish caught, some people stretch the truth on MPG. Until you both fuel at the same time/same pump and drive the route at the same time and refuel(again same pump) and hand calculate your mileages you do not know for sure that he is getting better mileage.

YEP, I have challenged many braggers to fill to the top both drive the same road then fill to the top. No takers!

 

[Cummins2014]

YEP, I have challenged many braggers to fill to the top both drive the same road then fill to the top. No takers!

i'm not taking you up on it, I know whats realistic, and whats not. No bragging, it is what it is. I know what my truck does, its comparable to most, not so much with the braggers as you say

 

[Rand Kibodeaux]

Well, it seems to be working now. The dealership must have actually done something other than give me grief because I bought it elsewhere. I just got back from a 200 mile excursion.

With the tow haul button on (the dashboard light has always come on), and the exhaust brake in full mode, it now brakes and downshifts very aggressively. There are teeth marks on the steering wheel to prove it.

I was only able to get the transmission to drop down a gear by engaging the tow haul button while I was on a steep incline. I was able to get it to do this several times today, but only while climbing, but the truck was empty and not towing anything. It’s the first time I’ve been able to do this. I tried it often on my 600 mile trip two weeks ago while towing my RV with no luck.

As far as the mileage issue, we’re talking about 60 mph two lane rural highways here in Idaho. When not towing and staying under 65, my truck will get 26 mpg. Repeatedly. Just not when towing. I have checked that manually, and the results with the dash computer are very close.

I really appreciate any and all responses! This diesel truck ownership is new to me and is quite a learning curve. I have learned a lot from the forum that I wouldn’t have known otherwise.

P.S. what the hell is the difference between 6th gear showing on the dashboard, and no gear showing on the dashboard?

 

[AH64ID]

Glad to hear it’s working now.

P.S. what the hell is the difference between 6th gear showing on the dashboard, and no gear showing on the dashboard?

When you use the ERS it shows you 2 numbers. Ones is the gear you’re in, the other is the highest gear you want it to use. It can be used to lock out higher gears, or manually select a gear.

There are minor shift point changes when using ERS too. It will hold gears longer than T/H, or so the stock 68RFE tune shows.