what is tow/haul mode

[coggonobrien]

i cant tell any differance in shift pts. what does it do?

[MadManAndrew]

It delays the shift points. It's pretty unnoticeable with gas motors unless you're really under load.
Posted via Mobile Device

[BarryB]

My 07 express van, has this. I usually am carrying quite a bit of weight, I can tell a difference when I switch to tow mode. What ^ said, it changes the shift points, keeps it in lower gears longer.

[Boog]

It's very noticeable on my 2000 GMC. It stays in the lower gears longer as said and shifts a bit firmer. I have used this in the winter to speed the engine warm up time.

[vern650]

i dont know if its the same in the gm trannys but in the allison it also causes the torque converter to lock up sooner and in all the gears, atleast thats what ive been told.

[clinebarger]

4L60E/4L80E Tow/Haul mode....

PURPOSE
Reduce the frequency and improve the predictability of transmission shifts when pulling a heavy trailer or a large or heavy load. This is most apparent in city traffic. Without tow/haul, the transmission may upshift on a closed throttle decel. With tow/haul, the transmission will hold the current gear on a closed throttle decel. This reduces upshifts and downshifts.
Provide the same solid shift feel when pulling a heavy trailer or a large or heavy load as when the vehicle is unloaded.
Improve control of vehicle speed while requiring less throttle pedal activity when pulling a heavy trailer or a large or heavy load.

FUNCTION
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).
Operation of tow/haul in a lightly loaded or non-loaded vehicle will not cause damage. However, there is no benefit to the selection of tow/haul when the vehicle is unloaded, this situation will cause a firm shift. The tow/haul switch is not a performance switch.
Selection of tow/haul when unloaded may result in unpleasant engine and transmission driving characteristics and reduced fuel economy. Tow/haul is recommend only when pulling a heavy trailer or a large or heavy load.
Examples of altered shift speeds when in tow/haul:
Minimum 1-2 shifts pushed out approximately 8 mph
Minimum 2-3 shifts pushed out approximately 15 mph
Minimum 3-4 shifts pushed out approximately 30 mph
Tow/haul only affects shift points below 55 mph.


Allison 1000 5-speed Tow/haul mode.....

Tow/Haul mode significantly changes the transmission shift pattern to reduce shift cycling and to deliver better performance, control, and cooling when towing or hauling heavy loads. For instance:

Upshift points are raised at light to mid throttle position to use more of the available engine power for acceleration. Downshift points are raised to enhance engine braking to help slow the vehicle.
During deceleration, the torque converter clutch (TCC) remains applied at closed throttle at lower speeds to significantly improve the effect of engine braking.
During acceleration, the TCC is applied in 2nd range and remains applied in 3rd, 4th, and 5th. This improves the drivetrain efficiency and significantly lowers transmission sump temperature when towing heavy loads. In Normal mode, the TCC generally applies only in higher ranges and is dependent on throttle position.
Tow/haul is designed to be most effective when the vehicle and trailer combined weight is at least 75 percent of the gross combined weight rating (GCWR) of the vehicle.
Operation of tow/haul in a lightly loaded or non-loaded vehicle will not cause damage. However, there is no benefit to the selection of tow/haul when the vehicle is unloaded. This situation will cause a firm shift. The tow/haul switch is not a performance switch.
Selection of tow/haul 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.

[Mykk]

Here is a screen shot from the tuning software I use; This is a factory cal for an '03 Silverado 1500 5.3/4L60E

Normal tables on the left, Tow/Haul (Known as Performance in the software) is on the right:




In tow/haul mode the PCM adds more line pressure to the transmission, but it also adds more torque management between shifts.