| Subject: | Driveline Characteristics for Four-Wheel Drive (4WD) System |
| Models: | 2004 Chevrolet Colorado |
The purpose of this bulletin is to help explain the operating characteristics
and differences of the new Colorado and Canyon 4WD system especially compared to other
light-duty truck models.
Disclaimer: Even though a certain amount of noise or feel can be expected, GM
may offer service procedures or components, or change vehicle design, which may reduce
perceived noise levels in the interest of customer satisfaction.
Important: For further information on driveline operating
characteristics, refer to GM Corporate Bulletin Number 01-04-18-001B.
The Colorado and Canyon transfer case has a Part-Time selectable electric shift
transfer case with a 2HI, 4HI, 4LO and a neutral position. These modes can be selected
by pressing the selector switch for the mode desired. The 4WD modes of Part-Time systems
do not allow for a difference in speed between the front and rear axles while turning.
This system effectively locks the front and rear propeller shafts together. When turning,
the tires must allow for the different turning radius of the front and rear axles,
which is why this is intended for low traction or off-road use. This system has low
range gearing for the transfer case. The RPO code for this transfer case is NP1 (T-150).
For additional operating instructions, please refer to the Owner's Manual.
| • | Shifting from 2HI to 4HI can be done at any speed. |
| • | Shifting from 4HI to 2HI can be done at any speed. |
| • | Shifting from 2HI or 4HI to 4LO must be done at 2 km/h (1.2 mph),
which is slower than walking. |
| • | When shifting to and from 4LO and out of neutral, some noise (grind or
clunk) can be expected along with a slight bump feel as the transfer case completes
the shift. |
| | This occurs because the 4LO range is not synchronized and there
may be a difference in transfer case input shaft and output shaft speeds, especially
if the vehicle is moving or equipped with an automatic transmission (residual torque
from the transmission may be driving the transfer case input shaft). To minimize the
noise, the shift may be completed at a stop and in an engine off, key on mode. However,
there may be an increased chance of having a blocked shift (the engine must be restarted
to complete the shift). Noise and bump levels will vary between vehicles and even
between shifts on the same vehicle. When driving in 4LO, the extra gear reduction
will make additional noise compared to driving in 4HI. The automatic transmission
shift characteristics will also feel different while operating in 4LO. |
| | Caution: Shifting the transfer case to neutral may
cause your vehicle to roll even if the transmission is in PARK (P). You or someone
else could be seriously injured. Be sure to set the parking brake before placing the
transfer case in neutral.
|
| • | A shift to neutral can only be made
from 2HI by holding the 2HI and 4LO buttons for 10 seconds. |
When requesting a shift if the proper conditions are not met, the indicator
light will flash for 30 seconds and default to the prior mode unless the shift is
requested again with the proper conditions.
