The 2005 tow/haul mode only changes the shift pattern, and doesn't lock out overdrive.

Is there a lead into the transmission that controls overdrive shifting, or is that all internal to the transmission? I want to find a way to lock out overdrive via an added in-cab switch. If OD engagement is externally controlled, which lead is it and just what would the switch need to accomplish - opening the circuit, tying it to ground, etc?

Along those same lines, can a harness modification be made to leave the truck in tow/haul mode continuously?

 

i am also interested in this.

I wonder what would happen if you went about putting a TQ converter lockup switch in with a 3 position switch. 1st position would be normal where the signal just passes through the switch. 2nd position would be to ground (if these are the same as 2nd gens) and you could lock it up. 3rd position would be open, so theoretically the transmission wont get the signal to lockup. I dont know if this would throw any codes or not though.

 

If I am not mistaken, Tow/Haul will also lock the converter in 2,3 and O/D...

on the 2005 anyway.

 

Two different issues. There is a procedure to lock up the TQ by shorting a pin on the transmission. I'm hoping to do something similar to lock-out the overdrive, if possible.

 

there is a box that will lock out o/d, t/h just lets the converter lock but does not keep it from going into o/d

 

I would assume there is no way to do it on your own because the dealer can reprogram the computer so the tow/haul becomes a OD lockout (but not both), so I believe it is all in the programming. You know what they say about ASSuming things though.

 

Yes there is another wire in trans control harness that will allow you control OD. The caveat is you have add some other controls to make it work correctly.

The OD circuit, like the lockup circuit, is continuously monitored for resistance between 5 ohms and 100 ohms. If you take control and break the circuit at will the off mode will need to include a resisted leg to ground to fool the ECU.

The next problem is in order to drop OD you will need to make sure the TC is unlocked first. Once TC lockup is engaged downshifting is locked out. So you would need to cut into an manage the lockup circuit the same way with a 3 position switch and a resisted leg.

The easier way to do it is go to BD Power and buy their lockout module. It reportedly works pretty well.

 

Thanks, checked with BD. $550 + shipping for the Torq-Loc and O/D Lockout modules together. Ouch. $225 for the O/D module alone. I'm towing the 10K pound trailer again this weekend. I'll see if it annoys me $600 worth.

I may try wiring a switch to open the O/D circuit (and fool the ECU with a, what, 50 ohm resistor?). I'd never open the circuit while already in O/D.

 

I've got the BD overdrive lockout, and it works exactly as I want. You can shut off the overdrive anytime, and have tow/haul with or without. Seems like a lot of money, but it's worth it. Turning off the OD on a cold morning will warm up the engine much quicker.

 

i just looked the o/d lockout is 213.99 at two places with free shipping,

 

That's looking better. Thanks.

 

Same here. The BD works great.