Tow/Haul mode

Rammer · May 5, 2002

When I use the tow/haul mode, the transmission seems to free-wheel when going downhill. The tach will drop to almost idle and no hold back can be felt. If I turn the tow/haul mode off, the trans engages again and the tach jumps back up to where it should be. I also noticed that the engine has to rev up 1,000 rpms before trans engages after letting off the throttle and coasting for a short piece with the mode "on". With the mode "off" the trans works great. Any ideas?

2002 Silverado Z-71 extended cab

5.3 with 4.10 locker

HillHound · May 6, 2002

When I use the tow/haul mode, the transmission seems to free-wheel when going downhill. The tach will drop to almost idle and no hold back can be felt. If I turn the tow/haul mode off, the trans engages again and the tach jumps back up to where it should be. I also noticed that the engine has to rev up 1,000 rpms before trans engages after letting off the throttle and coasting for a short piece with the mode "on". With the mode "off" the trans works great. Any ideas?

2002 Silverado Z-71 extended cab

5.3 with 4.10 locker

How much weight are you towing and at what speed does the "free-falling" happen? Are you driving in overdrive?

My truck, with the T/H engaged, does what seems like the exact opposite of what you're describing. In other words, it seems to keep the transmission locked in a lower gear than it would be in at the same rps with the T/H off.

The tow-haul programming is designed to keep the tranny in a lower gear longer at a given rpms in order to keep rpms high enough to keep the truck from shifting gears too often.

Short of getting the truck loooked at by a GM garage, the only other thing I can think of is that the truck's "computer" hasn't learned your driving habits enough yet to work properly, but that sounds kind of far-fetched. How many miles are on it? :idontgetit:

gandolphxx · May 6, 2002

I don't think the 4L60E learns like the Aliison, your description sounds like something is not quite right, I would make a dealer stop high on the list. ;)

ClipperSkipper · May 6, 2002

. The tach will drop to almost idle and no hold back can be felt.

What happens when you select D or 2 when going downhill?

This should provide some engine braking whilst decending a hill

and let you maintain control of your vehicle combination (truck/trailer). You cannot hurt the transmission by selecting a lower gear in order to slow the vehicle, according to GM Engineers. Be interting to see your findings.

Hope that my post helps.

99silveradoz71 · May 7, 2002

Yes, tow/haul holds the gear ratios longer. I've only tried it while not towing/hauling and not downhill, so I can't relate anything there. Worked nice for some off the line pickup once though.

Rammer · May 7, 2002

Hillhound, The truck can be empty or loaded and it and happens at all speeds with the selector in "D". The trans never shifts into 4th gear with the T/H on. I noticed it once with the selector in "3" also. When letting off the throttle, the tach will go down to 800 rpms, reguardless of road speed, get on the gas and the engine revs up to match road speed in 3rd gear. I'm taking it in for the 3,000 mile service and I'll add that to the list.

I holds in gear longer on the upshifts and somtimes downshifts too soon. If I slow to about 30 mph to go around a sharp bend in the road, the trans will shift all the way to 2nd gear after getting back on the gas, turning about 2800 rpms after dropping to 800 rpms and coasting. Not quite the "towing" mode I would prefer.

Clipperskipper, I haven't noticed that problem in "2". I always manually downshift to help with the downhill braking.

carguru · May 7, 2002

Unfortunately, I think that is normal for tow/haul mode. I had it do it in my '99. After I found this, I check my Dad's former '99 and a rental '00. They all do this. My '02 does this. It does this when you let off the gas, with or without a load. The dealer's explaination for this is that because the tranny is holding the shift instead of hunting for the right gear. This program is suppose to keep the tranny fluid cooler.