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The Hummer Knowledge Base
TT4 works best when the RPM range of the engine is in the middle of the torque curve. That's about 1400-1700 RPM depending on your source. Having the engine in the torque curve helps drive the drive over the obstacle the quickest and gives the maximum grunt to the wheels.
TT4 works best when the RPM's are held steady and unvarying as you going up the obstacle - a changing RPM will confuse the system and you end up with less effective traction. Wedging the side of your foot against the tunnel and rolling into the throttle instead of pressing it helps isolate it from bounces.
TT4 shuts off when the brakes are applied as the system goes into ABS mode - and take a moment to reactivate when brakes are released and the throttle is applied again. If your up in the air, you will probably roll backwards once you touch the brakes until they grab and then further backwards as you go back onto the throttle.
The TT4/ABS module can overheat and will automatically shut itself off after a minute or two (does anyone know the exact time?) of use for a rest period.
The earlier versions of TT4 (pre-2002) require fair amounts of wheel-spin in order to work. The 2002 system is much more sensitive and more aggressive in it's application. The new Torsen's used with the higher bias ratio help a bit too - which means you can also use Brake-Throttle-Modulation (BTM) more like the Pre-99's. But it's still less effective than the pre-TT4 trucks.
On slippery slopes, the ABS can kick in on descents and keep you sliding - Not a good feeling when your sliding toward a ledge as I've done several times. It's advisable to never get the truck sliding with TT4/ABS, if you can avoid it off-road, as you won't enjoy the ride if the ABS kicks in and keeps you from stopping...
The sensors on the pre-2002/3 TT4 trucks will often back away from the tone-ring. The bracket design was changed sometime in 2002 I believe to something a little more robust. If you get a dash warning light, go around to each of the geared hubs and look at the sensor mounted behind the half-shaft against the tone-ring. Press in any that may have slid out (usually you can see the cleaner spot where the sensor was covered) and restart the truck. Drive it a short distance to see if that solved the warning light problem.
That's all I can think of off the top of my head - but there is more to know about TT4 and using it effectively than 1200 RPM... Using it well would cover another page - but comes with experience.
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