Circuit Description

WARNING: This page is about a different car, the 2005 Cadillac STS. However, it is still accessible from the selected car via links, so may be relevant.

The transmission manual shift shaft switch assembly is a sliding contact switch attached to the lower control valve body within the transmission. The four inputs to the transmission control module (TCM) from the switch indicate which position is selected by the transmission selector lever. This information is used for engine controls as well as determining the transmission shift patterns. The input voltage at the TCM 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. The 4 IMS input parameters represented are Signal A, Signal B, Signal C and Signal P.

If the TCM detects a short to ground on the IMS signal A, then DTC P1820 sets. DTC P1820 is a type B DTC.