[okiemudslinger]

I just brought this truck and I was telling my son about some of the thinks it has and he asked about the tow mode switch and I told him it changes shift points in the transmission but when I push the button nothing same to happen no light on the dash nothing. I'm right there should be a light or something right?

 

[Pikey]

A light should come on the dash when the mode is engaged. Check out this thread starting with the 9th post

http://www.gmtruckclub.com/forum/showthread.php/91543-Tow-Haul-Mode-Probelm?highlight=haul+mode

 

[j cat]

GM made this wire to the tow mode switch too short. see if you can make the wire longer where the break is by about 1 inch.

 

[buckmeister2]

okie, the fix is not too hard. take a look at the pic in the post that Pikey indicated above. When you take your under dash cover off the right side, and remove the column covers, you will see what looks like an orange wire, but that is actually the sheath over two very fine wires, and those are likely broken. I modified the black loom holder a bit so there was more slack in the orange sheath & wires, then located the breakin the wires. I peeled back the insulation from each of the tiny wires where they were broken, and twisted the wires back together. Then, I used superglue to coat them, bent the repaired ends so they lay flat against the insulation--in opposite directions so the two wire repairs could not contact each other--and wrapped with a few rounds of electricians tape. Put it all back together, and it lights up and works fine. To clarify on the "tow mode"...having the button on does not affect the upshift point. In other words, it won't hold a higher rpm before shifting. However, it does affect the downshift point, meaning it will drop out of Lockup and OD a bit sooner with the button on to prevent lugging the engine, and overheating the tranny. At least, that is what all of my Silverado's with the button did.

 

[Pikey]

okie, the fix is not too hard. take a look at the pic in the post that Pikey indicated above. When you take your under dash cover off the right side, and remove the column covers, you will see what looks like an orange wire, but that is actually the sheath over two very fine wires, and those are likely broken. I modified the black loom holder a bit so there was more slack in the orange sheath & wires, then located the breakin the wires. I peeled back the insulation from each of the tiny wires where they were broken, and twisted the wires back together. Then, I used superglue to coat them, bent the repaired ends so they lay flat against the insulation--in opposite directions so the two wire repairs could not contact each other--and wrapped with a few rounds of electricians tape. Put it all back together, and it lights up and works fine. To clarify on the "tow mode"...having the button on does not affect the upshift point. In other words, it won't hold a higher rpm before shifting. However, it does affect the downshift point, meaning it will drop out of Lockup and OD a bit sooner with the button on to prevent lugging the engine, and overheating the tranny. At least, that is what all of my Silverado's with the button did.

I was told by a GM tech that Tow/Haul mode simply raises the RPM at which the transmission shifts for a given accelerator position, thereby giving better acceleration. It does not stop the tranny from going into Overdrive and does not stop the torque converter from locking up. I was also told that it locks out OD below 64 MPH. But, this is what I have been told. I have not seen it in writing from GM, so take it for what it is worth.
@ 99'HEARTBEAT is magic with coming up with info like this. Maybe he will have a chance to chime in.

 

[99'HEARTBEAT]

As per the Manual: Vehicles with an Automatic Transmission have a Tow/Haul Mode:

***The Tow/Haul Mode adjusts the Transmission Shift Pattern to Reduce Shift Cycling, providing Increased Performance, Vehicle Control, and Transmission Cooling when Towing or Hauling Heavy Loads.

***The Selector Button is located on the end of the shift lever. Turn the tow/haul on and off by pressing the button. When the tow/haul is on, a light on the instrument panel cluster will come on.


The Information Below is Also from the Owners Manual,

The purpose of the Tow/Haul Mode is to:
***Reduce the frequency and improve the predictability of Transmission shifts when pulling a heavy trailer or a large or heavy load.
***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.

Automatic Transmission equipped vehicles are provided with a button at the end of the shift lever which when pressed enables Tow/Haul.
***When the button is pressed, the Tow/Haul has been selected. Tow/haul may be turned off by pressing the button again, at which time the indicator light on the instrument panel will turn off.
***The Vehicle will automatically turn off Tow/Haul every time it is started.
***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).


This information Below is Also for the Owners Manual,
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. __________________

My Buddy, who is a Tech, and explained to me, when the Tow/Haul Mode is engaged.... It Increases the line pressure, which allows for Quicker/Firmer Shifts.....which Means Less Slippage of the clutches when Shifting while Towing......this Slippage, which I call Hunting and/or Surfing the Transmission does, means More Heat, and.....Heat is one of the Killers of Automatic Transmissions!!!

The Below Video shows step by step, on how to repair the Tow Haul Button"Orange Wire"

http://youtu.be/FtXPwPrXhFc

​

 

[buckmeister2]

Pikey, I would take the word of the GM tech over my limited testing. The change in upshift point seems possible, but I was thinking our trannies, under normal WOT operation, upshift at the highest rpm the factory would feel safe setting. So, how could they justify shifting at a higher RPM by pushing a button? I certainly could be wrong about that, and there certainly are a couple hundred safe RPM above the factory set point, no doubt about that. I will run mine out before too long and see about the OD being locked out under 64, also..that is easy enough to check, and would certainly make sense. All I know is I put mine in "tow/haul" when hauling over anything but flat highway, with no wind...I can't stand the constant up and down shifting when I have my cruise on.

 

[Pikey]

As per the Manual: Vehicles with an Automatic Transmission have a Tow/Haul Mode:

***The Tow/Haul Mode adjusts the Transmission Shift Pattern to Reduce Shift Cycling, providing Increased Performance, Vehicle Control, and Transmission Cooling when Towing or Hauling Heavy Loads.

***The Selector Button is located on the end of the shift lever. Turn the tow/haul on and off by pressing the button. When the tow/haul is on, a light on the instrument panel cluster will come on.


The Information Below is Also from the Owners Manual,

The purpose of the Tow/Haul Mode is to:
***Reduce the frequency and improve the predictability of Transmission shifts when pulling a heavy trailer or a large or heavy load.
***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.

Automatic Transmission equipped vehicles are provided with a button at the end of the shift lever which when pressed enables Tow/Haul.
***When the button is pressed, the Tow/Haul has been selected. Tow/haul may be turned off by pressing the button again, at which time the indicator light on the instrument panel will turn off.
***The Vehicle will automatically turn off Tow/Haul every time it is started.
***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).


This information Below is Also for the Owners Manual,
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. __________________

My Buddy, who is a Tech, and explained to me, when the Tow/Haul Mode is engaged.... It Increases the line pressure, which allows for Quicker/Firmer Shifts.....which Means Less Slippage of the clutches when Shifting while Towing......this Slippage, which I call Hunting and/or Surfing the Transmission does, means More Heat, and.....Heat is one of the Killer of Automatic Transmissions!!!

The Below Video shows step by step, on how to repair the Tow Haul Button"Orange Wire"

http://youtu.be/FtXPwPrXhFc

​

Thanks Mike! I knew that you would show up.

Pikey, I would take the word of the GM tech over my limited testing. The change in upshift point seems possible, but I was thinking our trannies, under normal WOT operation, upshift at the highest rpm the factory would feel safe setting. So, how could they justify shifting at a higher RPM by pushing a button? I certainly could be wrong about that, and there certainly are a couple hundred safe RPM above the factory set point, no doubt about that. I will run mine out before too long and see about the OD being locked out under 64, also..that is easy enough to check, and would certainly make sense. All I know is I put mine in "tow/haul" when hauling over anything but flat highway, with no wind...I can't stand the constant up and down shifting when I have my cruise on.

When I towed my 3500 lb boat I would use tow/haul. All 3 trucks seemed to ride out the gear forever. I would actually shift out of T/H often on flat ground because I could not stand the RPM's going so high before a shift. I would still leave it on when going up hills. As far as compared to WOT shifting goes, I could not tell you. My trucks very rarely see WOT.