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2016 2500 HD trans doesn't shift up when towing


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Last June a buddy of mine bought a twin to my new HD. 6.0, 6 speed, 4:10, CC, Z71 4,800 miles currently. He and his wife were towing their trailer from Vegas to Laughlin. The transmission would not shift up as it should. Nothing changed when shifting down to M5, M4, I asked if it was operating in 4WD but their answer was always in 2WD. Without the trailer, it behaves normally. Anyone have an idea? They will be taking it to a Vegas area dealer next week.

Edited by RamblinFever
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Sure its not in Manual mode? And they have 5th or 6th locked out?? Tow haul mode as well? And how do you mean it would not shift up as normall? It would shift up at a higher rpm? Or would not shift up at all?

Edited by 2016HD
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While Tow/Haul mode does not restrict 5th and 6th gear I had an issue once where a combination of poor gas, hot weather, and a constant uphill grade prevented me from doing the speed limit unless I was in 4th gear. I did not want to run 60+ miles in 4th trying to do 65 so I dropped my speed down to 50 and then the tranny shifted into 5th.

 

The next time I made the same trip, I had better gas and a cooler day and everything was fine.

 

Another possibility is that the tow/haul programming is off.

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Doesn't Tow/Haul mode disable being able to go into Overdrive? I thought that was the point so it eliminates "shift hunting" when getting close to the shiftover point into overdrive. What is it, 40-45 mph?

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Doesn't Tow/Haul mode disable being able to go into Overdrive? I thought that was the point so it eliminates "shift hunting" when getting close to the shiftover point into overdrive. What is it, 40-45 mph?

Tow/Haul mode changes the shift points and the torque converter lock up - it does not lockout the OD gears. In my 6sp it tends to keep the RPMs above 2000.

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Yeah, tow haul will just modify the shift points. It actually will make the trans run hotter.

 

If moderately loaded, mine won't shift up. In T/H, mine won't hit 6th until 65mph with very little load on the engine. These computer controller deals don't act like the old school hydraulic transmissions.

 

Sent from my SAMSUNG-SM-G900A using Tapatalk

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Tow/Haul is designed to be most effective when the vehicle and trailer combined weight is at least 75% of the vehicle's Gross Combined Weight Rating (GCWR). See “Weight of the Trailer” under Trailer Towing on page 9-76. Tow/ Haul is most useful under the following driving conditions: . When pulling a heavy trailer or a large or heavy load through rolling terrain. . When pulling a heavy trailer or a large or heavy load in stop-and-go traffic. . When pulling a heavy trailer or a large or heavy load in busy parking lots where improved low speed control of the vehicle is desired. Operating the vehicle in Tow/Haul when lightly loaded or with no trailer at all will not cause damage. However, there is no benefit to the selection of Tow/Haul when the vehicle is unloaded. Such a selection when unloaded may result in unpleasant engine and transmission driving characteristics and reduced fuel economy. Tow/ Haul is recommended only when pulling a heavy trailer or a large or heavy load.

 

The OP may need to do some math to see where he is at with the trailer weight/tongue weight/ overall weight etc. If his trailer is well under 75% of the trucks tow capacity he may well choose to leave the tow/haul button alone?

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The original post description is strange. If you use manual mode and shift down it will force a downshift. If that is not happening something is wrong. If you manual shift up it may or may not shift up depending on the situation but you can't manually force an upshift, only downshift.

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As stated, tow/haul mode will make it hold the lower gears longer, to avoid constant shifting. If they're towing a large trailer (especially into a headwind using cruise control), it's possible that the computer wouldn't let it go higher than 4th gear to maintain interstate speeds. How "high" of RPM's were they running?

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Sounds like its operating normally. Every response I see seems to be in the same line.

 

The original post description is strange. If you use manual mode and shift down it will force a downshift. If that is not happening something is wrong. If you manual shift up it may or may not shift up depending on the situation but you can't manually force an upshift, only downshift.

 

If the truck is in 4th already, and they drop to M4 from M5, its not going to downshift. If they were in 4th, and then dropped from M4 to M3 it would have downshifted to 3rd and then really screamed.

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