Allison Neutral Start Back Up Switch | 29540479 | 2001-2004 Chevy/GM Duramax LB7

This switch easily installs with just common hand tools. 

 

How does it work and why does it cause my transmission not to shift?

 

 

The vehicle is equipped with a column type shift selector. In addition to the column shifter, another component associated with the shift selector is the Neutral Start Back Up (NSBU) switch mounted on the selector shaft of the transmission. The NSBU switch transmits selector position information to the TCM. The NSBU 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 neutral signal output of the NSBU switch is typically used as confirmation that the transmission is in NEUTRAL or PARK before the engine starter is engaged.