Internal Mode Switch (IMS)
Internal Mode Switch (IMS)
The IMS contains 6 separate switches in one assembly. One mechanical switch circuit is for the park/neutral position switch which is used for engine starting. The other 5 electronic switches are called the transmission range switches and are used to indicate the gear position the vehicle operator has selected. The IMS switch assembly is mounted on the interior left side of the transmission case.
Park Neutral Position Switch of IMS
The park/neutral position switch indicates to the Engine Control Module (ECM) if the vehicle is in park/neutral or in a drive gear range. With the ignition ON, the ECM provides 12 V on the park/neutral signal circuit to the park/neutral position switch. A separate ground wire from the park/neutral position switch to chassis ground completes the circuit. When the gear shift lever in park or neutral, the switch closes and drops the voltage on the signal circuit to 0 V. In this state the engine will start and run. In reverse or drive range the park/neutral position switch opens, 12 V is then present on the signal circuit which will inhibit engine starting.
Transmission Range Switches of the IMS
The internal mode switch (IMS) indicates to the transmission control module (TCM) which gear position the vehicle operator has selected. The IMS consists of 5 separate hall effect switches. Each hall effect switch is supplied a 9 V reference circuit, and a signal circuit from the TCM. Each signal circuit for each gear selector position will have either a voltage reading of 0.70 - 0.96 V indicting ON or 1.68 - 2.38 V indicating OFF. The voltage values on each IMS circuit will change and are dependent on the position of the gear selector. The state of each IMS A/B/C/P/S circuit is displayed on the scan tool.