Mechanics

TRANSMISSION

2002 GMC C2500

Transmission problem
2002 GMC C2500 V8 Four Wheel Drive Automatic 110000 miles

I have a 2002 GMC Sierra 2500HD w/ allison transmission. When I pull the shifter into drive the letter D does not highlight anymore showing that I'm in drive. The truck stills goes into drive until today when it would only go into park and reverse. It did go into drive after trying a couple of times. There isn't any noise or any other issues.
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Rfdr3b
January 18, 2010.



The vehicle is equipped with a column-type gearshift lever. In addition to the column gearshift lever provided for the operator, another component associated with shift selection is the Park/Neutral Position (PNP) switch mounted on the selector shaft. See Fig. 4 . The PNP switch transmits selector position information to the TCM. The PNP switch mounts directly onto the transmission housing from the outside, and detects the angular position of the shift selector shaft. This position is communicated to the TCM so that certain vehicle control functions can be coordinated with the position of the shift controls. The PNP switch has redundant circuitry to alert the TCM in the event of a single wire or switch failure. The Neutral signal output of the PNP switch is typically used as confirmation that the transmission is in Neutral before the engine starter is engaged. The PNP switch is interfaced to the starter circuit with weatherproof electrical connectors. The Reverse signal provision may be used to activate vehicle back-up lights and/or Reverse warning devices.

The operator chooses the transmission gear range by moving the gearshift lever to the appropriate gate position. When properly adjusted, the shifter gates prevent inadvertent shifting between gear ranges, and correspond to the internal transmission detent positions. A positive detent is provided in the transmission to maintain the selector shaft in the selected position. The TCM shift calibration determines the available forward gear ranges for each gearshift lever position. Although specific installations vary, typical gearshift lever positions for the 1000 series are:

P - Park. The parking pawl is engaged. The transmission is in Neutral. This position is not available on all shift selectors. When available, may be used when starting the engine and for stationary operations. R - Reverse is selected to move vehicle backward. N - Neutral may be used when starting the engine and for stationary operations. The TCM disables the starter switch if a range other than Neutral or Park is selected before starting the vehicle. D - Drive is the highest forward range, and is used for normal driving. The transmission shifts to 1st gear for starting, and then automatically upshifts through the gear ranges (as operating conditions permit) until the highest gear range is attained. 4, 3, 2, 1 - There are four forward gear range selector positions. The first position after N (Neutral) is D (Drive), where all five forward gear ranges are available. Another position is first range hold. There are three choices for the next two positions. These choices are 1-4, 1-3, and 1-2, which describe the gear ranges available in that position. The vehicle manufacturer chooses the two positions that best fit the vocation for which the vehicle is intended.


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Due to the high volume of no responses to posted questions, if you have not resolved your issue and you need further assistance, please respond.

Dr Loot
Jan 25, 2010.