2001-2004 Duramax Allison 1000 NSBU Switch (29540479)

Fits

One of the most common problems with the Allison transmissions on 2001-2004 GM Duramax diesel-equipped trucks is a failed NSBU switch. The NSBU is the Neutral Safety Back Up Switch and a failed switch can cause your truck not to start. 

Part Number: 29540479

• High-Quality
• OEM Direct Replacement
• Simple Install

• 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 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 be set. The NSBU is subject to water contamination and will allow the switch to give faulty readings.

Symptoms Of NSBU Switch Failure

When diagnosing an NSBU switch failure, you are going to want to look for these common 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 A Duramax NSBU Switch Work?

The 2001-2004 Duramax diesel engine trucks are equipped with a column shift selector. The neutral safety backup, or NSBU switch) is another component that is associated with the column shifter, only it is mounted on the selector shaft of the transmission. This switch transmits the current selector position information to the transmission control module. Mounting directly on the transmission housing from the outside, the NSBU switch detects the angular position of the shift selector shaft. It then sends this position information 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.