Tow/Haul and SCT

[spindrift]

Please explain the mechanical/electronic operation of the Tow/Haul mode. Does it simply drop the tranny into a lower gear and that's what slows you down? I say this only because the engine starts to scream at higher RPMs once you brake in T/H.

Secondly...does an SCT program work with the T/H mode or is it an independent function? I've heard that an SCT tune can increase engine backpressure to help slow you down, much like the "TurboBrake" which controls the exhaust backpressure valve on some trucks. My '04 has an exhaust pressure sensor in the turbo, but no EBV (as far as I know). Does the SCT somehow control my/our EPS?

In my book, nothing beats the durability and effectiveness of Jake brakes in the big rigs. Is the SCT tow tune just as, if not better than, exhaust brakes?
I'm interested in the SCT, but I'm a little concerned if it's doing something in T/H mode that will reduce the longevity of my engine.

 

[DaveBen]

T/H works just like you described. It uses the engine's compression to slow down the truck. I don't know about the SCT or anyother chip/programmer.

Dave

 

[Black_Mamba]

From my understanding what it does is instead of simply shutting overdrive off it changes the shifting and locks the torque convertor in. It does some other things but can't remember all of them. The Tcm and PCM work hand in hand the whole time sensing everything that is going on. Say you hook up to a big load you press the tow/haul button and they both go crap now we have to work so the trans holds the gears longer and you are more able to stay in overdrive longer. It is awhole lot better feature than just shutting off overdrive. Lot less stress on the trans also.

 

[CBSuperDuty]

This is according to my little Cuban buddy... "The tow haul works with the transmission when the computer tells it to downshift. The SCT is based on the same principle."