Circuit/System Description

WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The drivers shift request (DSR), also known as the TAP Shift, allows the driver to select the desired range of gears for current driving conditions. Pressing the plus (+) switch will increase the highest attainable gear and pressing the minus (-) switch will decrease the highest attainable gear. The TCM will not allow a downshift if the transmission is compromised by over-speeding. The DSR shift switch is a resistor array and is located on the automatic transmission gear shift lever. The BCM supplies a 12 volt reference circuit and signal circuit to the DSR. The DSR shift system is activated when the gear selector is in the Manual (M) position. The DSR system is deactivated in all other range positions.

The tow/haul mode enables the operator to achieve enhanced shift performance when towing or hauling a load. When tow/haul mode switch is pressed and released, the tow/haul switch signal circuit to the BCM is momentarily toggled to zero volts. The BCM communicates the tow haul switch input to the TCM via GMLAN. When tow/haul mode is active, the transmission control module (TCM) changes the shift pattern to generally raise the output speed that an upshift or downshift is made and also applies the TCC in second range. When the tow/haul mode switch is pressed and released again, the BCM communicates the request to the TCM and tow/haul mode becomes inactive. The transmission upshift and downshift speeds and TCC command return to a normal shift pattern.