Wiring Systems and Power Management - Description and Operation Chevrolet Malibu VIII

Electronic Park Lock Description and Operation

If the vehicle is equipped with automatic transmission and a floor mounted console gear shift, it has an electronic park lock system (EPL). The EPL system purpose is to prevent the ignition key from being turned to the OFF position when the transmission is in any position other than PARK and the vehicle may still be moving. The EPL system consists of an ignition lock cylinder solenoid, and a park position switch that is located in the A/T shift lock control switch. The ignition lock cylinder solenoid contains a pin that is spring loaded to mechanically prevent the ignition key cylinder from being turned to the lock position when the vehicle transmission is not in the PARK position. If vehicle power is lost, and/or the transmission is not in the Park position the operator will not be able to turn the ignition key to the lock position and will not be able to remove the ignition key from the column.

Power Mode Description and Operation

Power to many of the vehicle circuits are controlled by the module that is designated the power mode master (PMM). The vehicle PMM is the body control module (BCM). The PMM controls which power mode (Run, Accessory, Crank, Retained Accessory Power, or Off) is active.

Serial Data Power Mode Master

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 body control module (BCM). The PMM receives 3 discrete ignition switch signals to differentiate which power mode will be sent over the Serial Data circuits. The 3-wire Ignition Switch table below illustrates the state of these inputs in correspondence to the ignition switch position

3-Wire Ignition Switch

Relay Controlled Power Mode

The body control module (BCM) uses the discrete ignition switch inputs Off/Run/Crank, Accessory, and ignition 1, to distinguish the correct power mode. The ignition 1 circuit is also routed to the Run/Crank relay for relay controlled power feeds during the appropriate power mode. The BCM, after determining the desired power mode, will activate the appropriate relays for that power mode.

Run/Crank Relay

The run/crank relay control circuit is connected to a constant ground and is switched by the ignition 1 circuit or the BCM. The BCM, will in lieu of the ignition switch position, activate the Run/Crank relay during a remote start event. The Run/Crank relay supplies a power signal to the following circuits, when the a Run or Crank power mode is selected

1. Automatic transmission shift indicator
2. Automatic transmission (A/T)
3. Switched power feeds to the BCM
4. Electronic brake control module (EBCM)
5. Electronic ignition module (spark control)
6. Electronic power steering module (EPS)
7. Fuel injectors
8. Powertrain control module (PCM)
9. Park neutral position (PNP) switch

Accessory (ACC) Relay

The adaptive cruise control (ACC) relay is energized when the Run or accessory power mode has been selected. The relay uses a Hot At All Times B+ power source derived from the underhood electrical center. The ACC relay is also energized by the BCM to supply power during the retained accessory power (RAP) mode. The following devices are controlled by this relay

1. Inside rearview mirror
2. Heated seats
3. Power windows
4. Sunroof
5. Wiper washers switch

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 power mode master (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 volts, 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.

BCM Wake-Up/Sleep States

The body control module (BCM) is able to control or perform all of the BCM functions in the wake-up state. The BCM enters the sleep state when active control or monitoring of system functions has stopped, and the BCM has become idle again. The BCM must detect certain wake-up inputs before entering the wake-up state. The BCM monitors for these inputs during the sleep state, where the BCM is able to detect switch transitions that cause the BCM 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.

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

1. Activity on the serial data line
2. Detection of a battery disconnect and reconnect condition
3. Headlamps are ON.
4. Ignition is turned ON.
5. Key-in-ignition switch
6. Park lamps are ON.
7. RFA message

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

1. The ignition switch is OFF.
2. No activity exists on the serial data line.
3. No outputs are commanded.
4. No delay timers are actively counting.
5. No wake-up inputs are present.

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

Retained Accessory Power (RAP)

The BCM monitors the ignition switch position, battery condition, and each door ajar/open switch status to determine whether RAP should be initiated or terminated. RAP is controlled with 2 different methods; serial data and relay control. Some modules receive a RAP message from the body control module (BCM) over the serial data circuits. Serial data controlled RAP is deactivated as required by their modules RAP power mode operation. Other subsystems are activated directly by the BCM through a RAP relay. Components and systems that are active in RAP are also activated anytime the ignition is any position other than OFF regardless of the door switch signals.

Relay Controlled RAP

The BCM keeps the RAP relay energized during all power modes, except Off-Awake and Crank. The relay is also energized for approximately 10 minutes after shutting the ignition OFF and removing the key, providing no door is opened.

Relay controlled RAP will end when one of the following conditions is met

1. The BCM receives an input from any door ajar or open switch indicating the opening of any door after the ignition key is out of the ignition. IMPORTANT: If the BCM is receiving any door ajar or open signal from those switches when the ignition key is turned OFF, RAP will not initiate.
2. The BCM internal timer for the RAP expires after approximately 10 minutes.
3. The BCM detects a decrease in battery capacity below a prescribed limit.

Systems powered by the accessory relay during the retained accessory power (RAP) power mode are as follows

1. Power windows
2. Sunroof

Serial Data Controlled RAP

RAP systems controlled by serial data are as follows

Radio

Radio RAP activation/termination is the same as relay operation with 1 exception; the only door switch that will turn off the radio during RAP is the driver door open switch.