In Tow/Haul Mode, the shift points in your automatic transmission are changed and the throttle response is increased for smoother starts and better acceleration under full load. Tow/Haul Mode holds lower gears longer while accelerating or decelerating, and for increased engine braking control.
For all practical purposed the Tow/Haul mode is a waste of time and confusing. It is just another ‘worthless’ convenience as far as I’m concerned. The idea is to allow your vehicle to have more ‘pulling’ power while pulling a load or improve fuel mileage on the highway while on. When ‘on’, it delays the shifts so the engine can build more power before it shifts, it also makes the shift quality more aggressive, It is also easy to forget to turn off.
We have a Tow/Haul mode on our 2000 GMC Safari van. We have never used it. We don’t tow or pull anything. However my experience with it as a transmission shop owner suggests that not to many folks know how to use it properly. That is my point, not to many people use it. My experimentation and study of Tow/Haul modes is to forget you have it and leave it out of Tow/Haul mode.
Technically speaking it uses a resistor to effectively lower the amperage to the pressure control solenoid, which in turn causes a later harsher shift. I found that the switch and circuitry used in these setups cause more trouble than they are worth, and add to that the fact that problems with this mode, whether electrical or mechanical are hard to diagnose.
My advise to customers who have questions about the Tow/Haul mode switch or when to turn the overdrive switch on or off is to forget you have them, leave overdrive on all the time, don’t get on the highway and forget to pop the overdrive switch on or you will lose as much a 4 or 5 miles per gallon. Leave the Tow/Haul switch off all the time.
One point of interest is that we never found any evidence that using a Tow/Haul switch actually increased pulling power or gas mileage.
That is my advise for this confusing option. If you have the option, learn to live with it. If not, consider yourself lucky you don’t have one more item to monitor.
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