Tow haul

[Rod Jr.]

When coming back from desert, came down Cajon pass with tow haul engaged. Truck downshifted once and then again to a lower range, heard a loud squealing sound at that point for a few seconds, thinking it must be because of the downshift I immediately turned off the tow command. After trying to engage tow haul mode when at bottom of grade, light works but the tow mode does not engage, any ideas ?

[Rod Jr.]

Looks like this has never happened to anyone else ?

[forddieseldoctor]

The pcm controls the light. I'm not sure why it would turn the light on but not let the truck go into tow-haul. Do you have any way to check codes?

[WarChild]

If it's not engaging then it should be blinking. You need to check for Trans codes.

[Rod Jr.]

The light did work but tow haul did not. Did not display any codes either. Tow haul is now working just driving around now without trailer, I just was curious how the tow haul actually works, and if something went wrong when descending down the pass. As stated earlier in post, loud squeal or siren type noise accompanied the harsh automatic downshift when trailer started to build up speed coming down hill. Also was not using cruise control at that time.

[Coach73]

I've had the tow haul not come on right away also (after shutting it off), seemed to take a few minutes before it was active again but it seems to work fine.

[forddieseldoctor]

Copied from the workshop manual:

Tow Haul

The Tow Haul feature was designed to assist the driver when towing a trailer or a heavy load. All transmission gear ranges, including all five forward gears, are available when using the tow haul feature.

The tow haul function is activated and deactivated through a switch located on the end of the shift lever. The indicator light that is located at the end of the shift lever will illuminate when the tow haul is activated and will go off when deactivated. On some models, the indicator light is located on the instrument panel.

With the tow haul activated, the transmission will have the following features:

Shifts will occur at higher vehicle speeds for a given accelerator pedal position to improve vehicle acceleration, reduce excessive shifting and increase the coast braking capability.
The torque converter will lock up at lower vehicle speeds than normal with a given accelerator pedal position to improve transmission cooling and efficiency.
Upshifts are temporarily delayed while decreasing accelerator position during hill cresting to reduce excessive transmission shifting and to prepare for a possible grade braking downshift event.
Engine braking is provided in all forward gears without the requirement of moving the shift lever.
Manual 1, 2 or 3 will still be available.
Grade braking downshift feature provides increased coast braking automatically to assist driver in maintaining desired speed while descending a grade. This reduces duty cycle on the brake system and increases brake pad longevity.
Grade braking downshifts are automatically commanded when:
positive vehicle acceleration is sensed (natural acceleration from grade descent).
a near zero accelerator pedal position is obtained.
a minimum amount of time has expired since the last grade braking downshift.
Grade braking downshift mode is immediately exited should the tow haul mode be deactivated or if the accelerator pedal is depressed beyond a minimum threshold.

[Arizona Dave]

The tow/haul doesn't do really change the operation of the engine like engaging a true engine brake or giving it any kind of 'boost'. It mostly affects the up and down shift points of the transmission.

When the tranny down shifted and the RPM's jump up, the serpentive belt speeds up rapidly along with it. All the components driven by the belt need to all speed up rapidly as well. If the belt tensioner is weak or if the belt is loose and glazed it can let out a whistle in the higher RPM range until it 'grabs'.

[WarChild]

Originally Posted by forddieseldoctor

Copied from the workshop manual:

Tow Haul

The Tow Haul feature was designed to assist the driver when towing a trailer or a heavy load. All transmission gear ranges, including all five forward gears, are available when using the tow haul feature.

The tow haul function is activated and deactivated through a switch located on the end of the shift lever. The indicator light that is located at the end of the shift lever will illuminate when the tow haul is activated and will go off when deactivated. On some models, the indicator light is located on the instrument panel.

With the tow haul activated, the transmission will have the following features:

Shifts will occur at higher vehicle speeds for a given accelerator pedal position to improve vehicle acceleration, reduce excessive shifting and increase the coast braking capability.
The torque converter will lock up at lower vehicle speeds than normal with a given accelerator pedal position to improve transmission cooling and efficiency.
Upshifts are temporarily delayed while decreasing accelerator position during hill cresting to reduce excessive transmission shifting and to prepare for a possible grade braking downshift event.
Engine braking is provided in all forward gears without the requirement of moving the shift lever.
Manual 1, 2 or 3 will still be available.
Grade braking downshift feature provides increased coast braking automatically to assist driver in maintaining desired speed while descending a grade. This reduces duty cycle on the brake system and increases brake pad longevity.
Grade braking downshifts are automatically commanded when:
positive vehicle acceleration is sensed (natural acceleration from grade descent).
a near zero accelerator pedal position is obtained.
a minimum amount of time has expired since the last grade braking downshift.
Grade braking downshift mode is immediately exited should the tow haul mode be deactivated or if the accelerator pedal is depressed beyond a minimum threshold.

Is this for all years of the 6.0?

[Rod Jr.]

Originally Posted by Arizona Dave

The tow/haul doesn't do really change the operation of the engine like engaging a true engine brake or giving it any kind of 'boost'. It mostly affects the up and down shift points of the transmission.

When the tranny down shifted and the RPM's jump up, the serpentive belt speeds up rapidly along with it. All the components driven by the belt need to all speed up rapidly as well. If the belt tensioner is weak or if the belt is loose and glazed it can let out a whistle in the higher RPM range until it 'grabs'.

Maybe thats what happened, but even though I tried several times later to re-engage, the tow haul light would come on but tow haul did not work.