Ignition Switch: Description and Operation

Conventional Ignition Switch - without Intelligent Access (IA)

Overview

The conventional ignition switch is controlled by the ignition lock cylinder and key. The ignition lock cylinder and ignition switch are connected mechanically, turning the lock cylinder places the switch into the desired position. The available ignition switch positions are:
- OFF
- ACC
- RUN
- START

When placed in any position other than OFF, the ignition switch provides voltage inputs to the BCM (Body Control Module). The BCM (Body Control Module) distributes this voltage to other modules and vehicle systems through the RUN/ACC and the RUN/START relays. The microprocessor internal to the BCM (Body Control Module) broadcasts an ignition mode network message over the MS-CAN (Medium Speed Controller Area Network) and the HS-CAN (High Speed Controller Area Network).

System Operation

System Diagram





OFF

When the ignition switch is turned to the OFF position, the BCM (Body Control Module) sends an "engine off" message to the other modules over the HS-CAN (High Speed Controller Area Network).

Acc

When the BCM (Body Control Module) receives the ACC voltage input from the ignition switch it activates the RUN/ACC bus and the RUN/ACC relay, providing ignition accessory power to the various vehicle systems and modules. The BCM (Body Control Module) also sends out the ignition mode message on the MS-CAN (Medium Speed Controller Area Network) and the HS-CAN (High Speed Controller Area Network).

RUN

When the BCM (Body Control Module) receives the RUN voltage input from the ignition switch it activates the RUN/ACC bus, the RUN/START bus, the RUN/ACC relay and the RUN/START relay, providing ignition power to the various vehicle systems and modules. The BCM (Body Control Module) also sends out the ignition mode message on the MS-CAN (Medium Speed Controller Area Network) and the HS-CAN (High Speed Controller Area Network).

Start

When the BCM (Body Control Module) receives the START voltage input from the ignition switch it activates the RUN/START bus and the RUN/START relay, providing ignition power to the various vehicle systems and modules. The BCM (Body Control Module) also sends out the ignition mode message on the MS-CAN (Medium Speed Controller Area Network) and the HS-CAN (High Speed Controller Area Network).

The ignition switch START circuit is also hard wired to the PCM (Powertrain Control Module). The PCM (Powertrain Control Module) uses the ignition switch START input to determine when to activate the starter motor relay. For additional information, REFER to Starting System Starting System - without Intelligent Access (IA).

Component Description

Ignition Switch

The ignition switch is a multiple position, rotary switch that is controlled by a lock cylinder and a key. The switch is hard wired to the BCM (Body Control Module), PCM (Powertrain Control Module) and the BSIA (Brake Shift Interlock Actuator).

The key removal inhibit solenoid (also known as the key release interlock actuator) is an electronically controlled solenoid that prevents the ignition lock cylinder from being turned to the OFF position unless the gear selector lever is in the PARK position. The key removal inhibit solenoid is part of the ignition switch.

Body Control Module (BCM)

The BCM (Body Control Module) determines the vehicle ignition mode based on the ignition switch input. The BCM (Body Control Module) communicates the ignition mode to the other modules over the MS-CAN (Medium Speed Controller Area Network) and the HS-CAN (High Speed Controller Area Network). The BCM (Body Control Module) monitors the ignition switch input and the ignition mode outputs, if a fault is detected in the ignition system DTCs (Diagnostic Trouble Codes) are set by the BCM (Body Control Module).

For additional information on the BCM (Body Control Module) functions, REFER to Body Control Module (BCM) Passive Anti-Theft System (PATS) - without Intelligent Access (IA).