Quick Ship SKU #: MA-10499 Merchant Automotive 10499 Allison NSBU Switch with Connector Repair Kit 01-04 6.6L GM Duramax LB7

One of the most common problems with the Allison transmission is failure of the Neutral Safety Back Up switch.

SYMPTOMS:

• No start condition
• Gear shift indicator on dash not following properly
• Trans stuck in limp mode or fail safe
• DTC's set indicating pressure switch codes

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 Safety 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.

The reason that PSM codes may set is that the NSBU switch and the internal PSM switch "look at each other" and "compare readings" Basically, the NSBU switch lets the TCM know what gear position that you, the driver, have selected. The PSM has the job of telling the TCM what gear the transmission is in based on hydraulic inputs. If the data received from the PSM and the NSBU do not agree, the above mentioned trouble codes may set. The NSBU is subject to water contamination and will allow the switch to give faulty readings.