Circuit/System Description

WARNING: This page is about a different car, the 2008 GMC Yukon XL, 2008 GMC Yukon, 2008 Chevrolet Tahoe, 2008 Chevrolet Suburban, and 2008 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

The transmission range (TR) switch is part of the park/neutral position and back-up lamp switch assembly and is externally mounted on the transmission manual shaft. The TR switch is a multi-signal switch. The transmission control module (TCM) supplies ignition voltage to the TR switch on 4 signal circuits, A, B, C, and P. Each gear selector lever position grounds one or more of the switch circuits. In order to determine the gear range selected by the driver, the TCM compares the voltage combinations on the signal circuits to a look up table stored in the TCM memory. TCM detects the selected gear range by the state change of the switch input. Refer to Transmission Range Switch Logic table.

Switch input to the TCM is represented on the scan tool as HI and LOW. HI indicates an ignition voltage signal. LOW indicates a zero voltage signal. The 4 parameters represent transmission range switch signal A, B, C and Parity.