GM Service Manual Online
For 1990-2009 cars only
Table 1: 4-Wire Ignition Switch Table

The body control system consists of the following 3 modules:

    • The dash integration module (DIM)
    • The instrument panel module (IPM)
    • The rear integration module (RIM)

Each of the 3 body control modules integrate a number of functional systems under the control of a single module. Each module is connected to the Class 2 serial data circuit, many of the control signals are implemented by Class 2 messages.

Dash Integration Module (DIM)

The various DIM input and output circuits are described in the corresponding functional areas as indicated on the DIM electrical schematics.

The DIM functions include the following:

    • A/C refrigerant low temperature sensor signal.
    • Air conditioning orifice solenoid control.
    • Backlight lamps control.
    • Control of headlights and exterior lamps.
    • Control power control.
    • DRL relay control.
    • Flash to pass signal.
    • Headlamps on w/wipers signal.
    • Headlamps switch signal.
    • Horn relay control.
    • Interior lamps incandescent dimming.
    • Power moding control over Class 2 serial data line.
    • Reverse lockout solenoid control.
    • Storage of the clock settings and, sending a message out on the class 2 serial data circuit in response to requests from other modules.
    • Steering wheel controls.

Serial Data Power Mode

On vehicles that have several control modules connected by serial data circuits, one module is the power mode master (PMM). On this vehicle the PMM is the DIM. The PMM receives 4 signals from the ignition switch.

To determine the correct power mode the PMM uses the following circuits:

    • Accessory voltage
    • Run/Crank voltage
    • Ignition 3 voltage
    • Off/Run/Crank voltage

4-Wire Ignition Switch Table

Ignition Switch Position

Accessory

IGN 3

Run/Crank

Off/Run/Crank

Power Mode Transmitted

Off

0

0

0

0

Off/Awake or RAP

Accessory

1

0

0

1

Accessory

Start

0

0

1

1

Crank

Run

1

1

1

1

Run

Fail-safe Operation

Since the operation of the vehicle systems depends on the power mode, there is a fail-safe plan in place should the PMM fail to send a power mode message. The fail-safe plan covers those modules using exclusively serial data control of power mode as well as those modules with discrete ignition signal inputs.

Serial Data Messages

The modules that depend exclusively on serial data messages for power modes stay in the state dictated by the last valid PMM message until they can check for the engine run flag status on the serial data circuits. If the PMM fails, the modules monitor the serial data circuit for the engine run flag serial data. If the engine run flag serial data is True, indicating that the engine is running, the modules fail-safe to RUN. In this state the modules and their subsystems can support all operator requirements. If the engine run flag serial data is False, indicating that the engine is not running, the modules fail-safe to OFF-AWAKE. In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle.

Discrete Ignition Signals

Those modules that have discrete ignition signal inputs also remain in the state dictated by the last valid PMM message received on the serial data circuits. They then check the state of their discrete ignition input to determine the current valid state. If the discrete ignition input is active, battery positive voltage, the modules will fail-safe to the RUN power mode. If the discrete ignition input is not active, open or 0 voltage, the modules will fail-safe to OFF-AWAKE. In this state the modules are constantly checking for a change status message on the serial data circuits and can respond to both local inputs and serial data inputs from other modules on the vehicle.

Electrical Load Management

The power management function is designed to monitor the vehicle electrical load and determine when the battery is potentially in a high discharge condition. This is accomplished by using a high accuracy battery voltage reading as an indicator of battery discharge rate. The following six levels of load management will execute in the load management control algorithm when there is a high discharge condition:

  1. The first action requests a vehicle idle speed increase to the powertrain control module (PCM) in order to raise alternator output.
  2. The second action requests a greater vehicle idle speed increase to the PCM in order to raise alternator output.
  3. The third action begins to shed vehicle loads in an attempt to remedy the heavy discharge condition.
  4. The fourth action requests another vehicle idle speed increase to the PCM in order to raise further the alternator output.
  5. The fifth action begins to shed further vehicle loads in an attempt to remedy the heavy discharge condition.
  6. If the above five corrective actions fail, the sixth action of power management further sheds loads in a final attempt to remedy the high discharge condition.

Loads subject to reduction include the following:

    • The A/C clutch
    • The heated mirrors
    • The heated seats
    • The rear defog
    • The HVAC blowers

The power mode master (PMM) calculates the battery temperature, voltage and charging rate at all times while the engine is running. The PMM calculates the battery temperature by factoring in:

    • The current intake manifold air temperature compared to the last temperature recorded when the ignition switch was turned OFF
    • The current battery voltage compared to the last battery voltage recorded when the ignition switch was turned OFF
    • The length of time since the last battery temperature calculation

If the battery temperature is below set limits, the PMM institutes steps to control the load.

The PMM calculates the voltage of the battery by making constant measurements and using the measurements to calculate the true battery voltage. If the PMM detects a low voltage, the PMM institutes steps to control the load.

The PMM calculates the discharge rate, or draw, on the battery by making constant measurements and using the measurements to calculate the discharge rate in amp/hours. If the PMM detects a high current draw from the battery, the PMM institutes steps to control the load.

The PMM will either request an increase in the engine idle speed to the PCM or the PMM will cycle or turn off loads, called the load-shed function, in order to preserve the vehicle electrical system operation. The criteria used by the PMM to regulate this electrical load management are outlined below:

Function

Battery Temperature Calculation

Battery Voltage Calculation

Amp-hour Calculation

Action Taken

Idle Boost 1 Start

<-15°C (5°F)

N/A

N/A

First level Idle speed increase requested

Idle Boost 1 Start

N/A

N/A

Battery has a net loss of 0.6  AH

First level Idle speed increase requested

Idle Boost 1 End

>-15°C (5°F)

N/A

Battery has a net loss of less than 0.2  AH

First level Idle speed increase request cancelled

Idle Boost 1 End

N/A

14.0 V

Battery has a net loss of less than 0.2  AH

First level Idle speed increase request cancelled

Load Shed 1 Start

N/A

N/A

Battery has a net loss of 1.6  AH

Controlled outputs cycled OFF for 20% of their cycle

Load Shed 1 End

N/A

N/A

Battery has a net loss of less than 0.8 AH

Clear Load Shed 1

Idle Boost 2 Start

N/A

N/A

Battery has a net loss of 5.0  AH

Second level Idle speed increase requested

Idle Boost 2 End

N/A

N/A

Battery has a net loss of less than 2.0 AH

Second level Idle speed increase request cancelled

Idle Boost 3 Start

N/A

N/A

Battery has a net loss of 10.0 AH

Third level Idle speed increase requested

Idle Boost 3 Start

N/A

<10.9 V

--

Third level Idle speed increase requested

Idle Boost 3 End

N/A

>13.0 V

Battery has a net loss of less than 6.0  AH

Third level Idle speed increase request cancelled

Load Shed 2 Start

N/A

N/A

Battery has a net loss of 12.0 AH

Controlled outputs cycled OFF for 50% of their cycle and BATTERY SAVER ACTIVE message is displayed on the DIC

Load Shed 2 End

N/A

N/A

Battery has a net loss of less than 10.5 AH

Clear Load Shed 2

Each load management function, either idle boost or load-shed, is discrete. No two functions are implemented at the same time.

During each load management function, the PMM checks the battery temperature, battery voltage and amp-hour calculations and determines if the PMM should implement a different power management function.

Idle Boost Functions

The PMM sends a serial data request to the PCM to increase the idle speed. The PCM then adjusts the idle speed by using a special program and idle speed ramp calculations in order to prevent driveability and safety concerns. The idle speed boost and cancel function will vary from vehicle to vehicle and from one moment to another on the same vehicle. This happens because the PCM responds to changes in the inputs from the sensors used to control the powertrain.

Load Shed Function

The PMM executes the load shed function, by controlling the relay coil or the inhibit circuit of the following devices.

    • The A/C clutch
    • The heated mirrors
    • The heated seats
    • The rear defog
    • The HVAC blowers

DIM Wake-up/Sleep States

The DIM is able to control or perform all of the DIM functions in the wake-up state. The DIM enters the sleep state when active control or monitoring of system functions has stopped, and the DIM has become idle again. The DIM must detect certain wake-up inputs before entering the wake-up state. The DIM monitors for these inputs during the sleep state, where the DIM is able to detect switch transitions that cause the DIM to wake-up when activated or deactivated. Multiple switch inputs are needed in order to sense both the insertion of the ignition key and the power mode requested. This would allow the DIM to enter a sleep state when the key is IN or OUT of the ignition.

The DIM will enter a wake-up state if any of the following wake-up inputs are detected:

    • Activity on the serial data line.
    • Detection of a battery disconnect and reconnect condition.
    • Headlamps are on.
    • Ignition is turned ON.
    • Key-in-ignition switch.
    • Parklamps are on.

The DIM will enter a sleep state when all of the following conditions exist:

    • Ignition switch is OFF.
    • No activity exists on the serial data line.
    • No outputs are commanded.
    • No delay timers are actively counting.
    • No wake-up inputs are present.

If all these conditions are met the DIM will enter a low power or sleep condition. This condition indicates that the DIM, which is the PMM of the vehicle, has sent an OFF-ASLEEP message to the other systems on the serial data line.

Instrument Panel Module (IPM)

The various IPM input and output circuits are described in the corresponding areas as indicated on the IPM electrical schematics.

The IPM functions include the following:

    • Ambient light sensor input and twilight delay input for headlights control.
    • Foglamp switch input.
    • Front HVAC air delivery and temperature controls.
    • Ignition switch headlight control.
    • Interior lamps switch input.
    • IP dimmer switch input.
    • Key cylinder lamp control.
    • Key-in-ignition switch input from the ignition switch.
    • Rear compartment lid release switch input.
    • Traction control switch input.

Rear Integration Module (RIM)

The various RIM input and output circuits are described in the corresponding functional areas as indicated on the RIM electrical schematics.

The RIM functions include the following:

    • Automatic level control.
    • CIGAR relay control.
    • Fuel door release relay control.
    • Heated seat controls.
    • Heating, ventilation, and air conditioning (HVAC) blower control.
    • Inadvertent power relay control.
    • Park brake relay controls.
    • Rear defogger relay control.
    • Rear foglamp relay control.
    • Retained accessory power (RAP) control.
    • Reverse lamp relay control.
    • Trunk ajar switch signal.
    • Trunk release relay control.
    • Various controls for the interior lamps.