Circuit Description

WARNING: This page is about a different car, the 2007 Cadillac DTS. However, it is still accessible from the selected car via links, so may be relevant.

The transmission internal mode switch (IMS) is a sliding contact switch attached to the lower control valve body, within the transmission. The manual valve link assembly then connects the IMS to the manual valve. The 4 inputs to the transmission control module (TCM) from the IMS 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 level at the TCM is high, ignition voltage, when the IMS is open and low when the switch is closed to ground. The state of each input is available for display on the scan tool. The four input parameters represented are Signal A, Signal B, Signal C and Signal P, Parity.

If the TCM detects an IMS transitional state between D4 and D3 while the vehicle is in motion, then DTC P1820 sets. DTC P1820 is a type B DTC.