Internal Mode Switch (IMS)

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

Fig 1: Internal Mode Switch (IMS)

Courtesy of GENERAL MOTORS CORP.

The internal mode switch (IMS) assembly is a dual sliding contact switch attached to the control valve body within the transmission. The nine outputs from the switch indicate which position is selected by the transmission manual shaft. Four outputs (A, B, C, P), are range selection inputs to the transmission control module (TCM). Five outputs (R1, R2, D1, D2, S) are direction selection inputs to the HPCM through the transmission 24-way connector. The input voltage at the modules is high when the switch is open and low when the switch is closed to ground. The state of each input is displayed on the scan tool as IMS Range and IMS Direction. The IMS Range input parameters represented are transmission range signal A, signal B, signal C and signal P. The IMS Direction input parameters represented are transmission direction signal R1, signal R2, signal D1, signal D2 and signal Start.