GTO V8-6.0L VIN U (2005)
(BCM) to sense whether a switch is open or closed. A voltage is applied to the switch through the pull-up resistor so that when the switch closes there
is not a short-circuit between the power and ground.
The BCM registers the voltage at the bottom of the pull-up to determine if the switch is open or closed. When the switch is open, there is no current
flowing in the resistor and therefore no voltage drop occurs across the resistor so the voltage sensed by the BCM is the supply voltage. When the
switch closes, a current flows in the pull-up resistor causing a voltage drop across the resistor. Because the bottom of the pull-up resistor is shorted to
ground, the voltage at the bottom of the pull-up resistor is 0 volt. This indicates to the BCM that the switch is closed.
CIRCUIT DIAGNOSTICS - PULL-DOWN
A pull-down resistor has one end connected to a switch and the other end connected to ground. The pull-down resistor allows the body control module
(BCM) to sense whether a switch is open or closed. When the switch is closed, a voltage is applied to the circuit and current flows through the
pull-down resistor so there is no short-circuit to ground.
The BCM registers whether the switch is open or closed by measuring the voltage at the top of the pull-down resistor. When the switch is closed, a
current flows through the pull-down resistor, which causes a voltage drop across the resistor. Because the top of the pull-down resistor is connected to
12 volts via the switch, the voltage at the top of the resistor is 12 volts. When the switch is open, no current flows in the pull-down resistor and the
voltage at the top of the resistor is then 0 volt.
CIRCUIT DIAGNOSTICS - PULSED PULL-UP
A pulsed pull-up circuit is similar to a conventional pull-up circuit, however the pull-up resistor has its voltage supply end connected to the battery
voltage via a switching transistor. At the output terminal side of the pull-up resistor, circuits such as the door ajar switches, door locks, power
windows, etc. are typical circuits using pulsed pull-up inputs to the body control module (BCM).
The purpose of the pulsed pull-up circuit is to briefly sample if a switch connected to it is closed or not. By using only a small of amount of sampling
time in which the switching transistor is turned ON, the circuit thereby reduces the current flowing in this type of circuit. When many of these circuits
are sampled in the same manner, the overall battery current is reduced considerably. This current reduction has quite a significant effect on battery life
when the vehicle is not being used for extended periods. In operation, if the externally connected switch is closed continuously, no current flows
through the pull-up resistor because the switching transistor has not been turned ON by the microprocessor. Periodically, approximately 100 sampling
pulses per second, the switching transistor is turned ON for a brief time to enable current to flow in the resistor. This action then allows the
microprocessor input circuit to sense whether there is voltage across the switch contact or not. Once it has made this measurement, the sampling pulse
is removed from the switching transistor and current ceases to flow in the resistor until the next sampling pulse repeats the above process.
SERIAL COMMUNICATION
The vehicle system control modules, as well as the TECH 2 diagnostic scan tool, communicate with each other via the serial communication lines
using serial data. Serial data transfers information, one bit at a time, over a single line called the data bus. Except for the engine control module
(ECM), all control modules communicating on the data bus use universal asynchronous receiver and transmitter (UART) communication. The UART
is a 5-volt data line that toggles the voltage to ground (0 volt) at a fixed bit pulse width during communication. The UART transmits data at the rate of
8.2 kilobits per second (8192 bits per second). In UART communications, when there is no communication on the data line, the system voltage is 5
volts.
BODY CONTROL MODULE BATTERY SAVER MODE
The body control module (BCM) battery saver mode provides vehicle battery protection through reduced current consumption. After a preset delay
period of 15 minutes has elapsed, as controlled by the shut down timer, the BCM:
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De-energizes the interior illumination relay, which supplies battery voltage to all interior dome, ignition lock, glove compartment, and rear
compartment lamps-This protects the battery when a lamp is mistakenly left on because a door is left open, or a faulty illumination circuit or
component is causing excess current consumption.
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De-energizes the power window relay-This action is separate from the normal power window off delay function.
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Disables the BCM inputs normally not required when the ignition is OFF-This reduces the BCM current consumption.
If the BCM is in battery saver mode, all the BCM inputs are re-enabled when:
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The bonnet, rear compartment or any door is opened.
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The BCM receives a valid RF key lock, unlock, or rear compartment signal.
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The ignition switch is turned ON or to the accessories position.
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The doors are unlocked via the driver door microswitch.
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TECH 2 is communicating with the BCM.
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The headlamp switch is cycled from OFF to ON or from ON to OFF.
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The rear compartment release switch, located in the glove box, is operated.
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The alarm is activated.
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The hazard switch is activated.
PRE-DELIVERY MODE
To provide additional battery protection, the vehicle is delivered with the body control module (BCM) in pre-delivery mode. In this mode the battery
saver period is set to 3 minutes. Pre-delivery mode is disabled once the vehicle has travelled for a total of 30 minutes at speeds above 20 km/h (12
mph). This value is estimated to be the equivalent period prior to customer delivery. Pre-delivery mode may be enabled or disabled by using the trip
computer buttons and multifunction display (MFD). Pre-delivery mode may also be enabled and disabled using a scan tool.
