1. UpFix FAQ's
  2. Automotive
  3. TCM Transmission Control

Gear shift indicator not working properly, the vehicle won't start, or the vehicle is stuck in limp mode (3rd gear) and won't move.

  • Cleaning the connectors on the plug and doing a hard battery reset may help. (Link for instructional video here)
  • The NSBU (Neutral Start Back-Up) Switch is mounted to the transmission and needs to be inspected especially the connector to make sure it's getting a good connection.
  • These are notorious for failing on the 2001-2005 Allison transmission, however, for 2009-2015, it should still be checked if it's still in limp mode.