Is the security light lit on the instrument when it doesn't start ? The ignition switch on your vehicle doesn't work like you would probably think it does . The ignition switch is input signal to the body control system .
Body Control System Description
The body control system consists of three modules and their associated electrical controls. These modules are as follows:
• The dash integration module (DIM), located on the right hand side of the instrument panel, near the blower motor.
• The instrument panel integration module (IPM), located in the center of the instrument panel, above the radio.
• The rear integration module (RIM), located on the right hand rear of the passenger compartment, behind the rear seat.
Each module integrates input and output controls for two or more functional areas. The inputs and outputs are wired to the closest module to minimize the lenth and amount of the wiring used. All three modules communicate on the Class 2 serial data line, allowing data to be shared among them, as well as with other Class 2 modules on the vehicle as needed.
Each of the three body control modules integrate a number of functional systems under the control of a single module. Each of the modules are connected to the Class 2 serial data line.
Dash Integration Module (DIM)
The dash intergration module (DIM) functions include the following:
• Power moding control (ignition switch states) over Class 2 serial data line
• Control of exterior lamps
• Interior lamps and incandescent dimming
• Steering wheel controls
• Horn relay control for theft activation
• Low side temperature for HVAC compressor
• Hood ajar switch input (export)
• Storage of the clock settings and, sending a message on the class 2 serial data line in response to requests from other modules.
Instrument Panel Integration Module (IPM)
The instrument panel integration module (IPM) functions include the following:
• Front HVAC air delivery and temperature controls
• Ambient light sensor input and twilight delay input for headlights control
• Foglight switch inputs
• I/P dimmer switch input
• Traction control switch input
• Interior lamps switch input
• Key in ignition switch input from the ignition switch
• Fuel door and rear compartment lid release switch input
• Ignition switch headlight control
Rear Integration Module (RIM)
The rear integration module (RIM) functions include the following:
• Fuel level sensor input
• Heated seat controls
• HVAC blower control
• Rear defogger control
• Park brake relay controls
• Various controls for the interior lamps
• Reverse control for the backup lamps and automatic day/night mirror
• Rear foglights control
• Fuel door and rear compartment lid release controls
• Retained accessory power (RAP) control for the sunroof control module
• Ajar switch and tamper switch inputs from the rear compartment lid
• Content theft alarm
At the dealer we would hook up a scan tool and look at the ignition switch inputs to the DIM to see if has correct inputs . Also we would check DTC'S diagnostic trouble codes .
DTC B1805 Ignition Switch Problem
Normal vehicle Class 2 communication does not begin until the system power mode has been identified. The dash integration module (DIM) monitors four discrete wires from the ignition switch contacts in order to determine the present power mode (ignition switch position). The DIM communicates the system power mode to all Class 2 modules on the Class 2 serial data line.