DTC P0708: Transmission Range Switch (ALLISON A/T): Description

WARNING: This page does not describe the selected car, but rather 13 other vehicles, including the 2002 GMC Yukon XL, 2002 GMC Sierra, 2002 GMC Savana Special, 2002 GMC Savana Camper Special, and 2002 GMC Savana. However, it is still accessible from the selected car via links, so may be relevant.

The installation of a transmission-mounted neutral start/reverse signal switch is required. This switch, commonly called a "Park/Neutral Position 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 Transmission Control Module (TCM) so that certain vehicle control functions can be coordinated with the position of the shift controls. The Park/Neutral Position (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.