Battery voltage is supplied to the body control module (BCM) by circuit 2540. This input is internally monitored by the BCM for proper operating voltage. The proper operating voltage range is from 9-16 volts.

The ground for the BCM is by circuit 550 through the I/P ground splice pack.

The BCM monitors ignition 1 voltage circuit 339, ignition 2 voltage circuit 743 and the engine run flag (ERF). The ERF is a serial data message from the engine controller. The BCM determines the state of the ignition switch for all modules on the serial data link.

The BCM performs an electrically erasable, programmable, read-only memory (EEPROM) checksum, as a part of its internal diagnostics as the BCM is operating. When the EEPROM checksum does not equal a predetermined value, the DTC B1000 -- ECU malfunction -- sets. The checksum is the content of each memory location in EEPROM added together.

The vehicle option content information must be entered as part of the BCM programming procedure. If the vehicle option content information is not included and the programming procedure is complete, the DTC B100 -- Option Configuration Error -- will set.

When the park brake input circuit 1134 to the BCM is grounded, such as when the parking brake is applied, the BCM will turn on the brake telltale by sending a serial data message to the instrument panel cluster (IPC).

If the vehicle is moving at greater than 3 mph and the park brake input to the BCM is grounded, the BCM will sound the warning chime to notify the driver that the parking brake is applied. The DTC B0005 -- Park Brake Switch Circuit Low -- will set under these conditions.

The class II serial data circuit 1807 is used to communicate information between modules, for example, between the body control module and the engine controller.

Contained in each module's memory is a list of serial data messages that are important and should be received by the module. Also contained are the default actions to be taken by the module, if one of the important messages is not received in time. One of those important messages is the state of health (SOH) message. This message is sent by the module, if no other message needs to be sent, to let all of the other modules on the serial data circuit know the sending module is working correctly.

Each time the ignition is turned ON, all modules on the class II serial data circuit first learn the other modules connected to the class II data circuit. Modules are able to learn the other modules on the serial data circuit, because each of the important messages has a source identifier as a part of the message.

This process of learning by a module allows the module to know if it has lost communication with a specific module on the class II data circuit.

The engine control module (ECM) and the transaxle control module (TCM) communicate with each other over the controller area network (CAN), bus circuit 2501 and circuit 2500. The CAN bus is a communication link similar to the class II.

The body control module (BCM) acts as the interpreter or gateway between the other modules connected to the class II serial data circuit 1807 and the ECM and the TCM connected to the CAN bus circuit 2501 and circuit 2500.

State of health (SOH) messages are sent from the ECM and the TCM to the BCM when the ignition is turned ON and during operation. These messages tell the BCM, the ECM and TCM are working correctly. The BCM has an internal reset counter to monitor the status of the CAN bus. When the counter reaches a defined value and no CAN messages have been received from either the ECM or the TCM, then the BCM sets the DTC U2104 -- the CAN Bus Reset Counter Overrun.

The anti-lockout feature aids in preventing the customer from locking their car keys in the vehicle. This is a programmable feature using the Tech 2. The options enable and disable the feature. The feature works as follows: If the keys are in the ignition and a manual door lock switch is activated, with any door open, the BCM will lock all of the doors. Then within 500 mS, the driver's door will unlock. This feature can be overridden in 2 ways:

The delayed locking feature will activate when a valid lock command is received from a transmitter while any door or trunk (hatch) remains open. The BCM will delay locking the vehicle until all doors and the decklid (hatch) are closed. The lock command will execute within 500 mS after all doors and/or the decklid transitions to closed. If during the delayed state a transmitter unlock command, door unlock switch input, or the ignition switch changes state to other than Off, the delayed locking command will cancel.

When the delayed locking feature is active, in the delayed state, the body control module (BCM) will activate a chime at a rate of 50 chimes per minute for a duration of 3 chime cycles. If the condition or state changes, the chime will continue until completion of the chime schedule.

This feature is available on all Saturn L-Series vehicles with a remote keyless entry (RKE).

The body control module (BCM) will provide an audible warning for various events relating to the vehicle. The functions that provide an audible warning are the key in ignition, the lights on, the occupant restraint (seat belt) and the park brake.

The BCM will provide an audible chime if the key is left in the ignition in either OFF or the accessory position with the driver's door open. The chime rate for this is 150 chimes per minute. The key in the ignition chime has a higher priority than the lights on chime.

The BCM will provide an audible chime if the park lights are on and the driver's door is open. In addition, 1 or 2 other conditions exist. The key is out of the ignition, or the key is in the ignition in the OFF position, and has not been turned. The BCM will chime at a rate of 200 chimes per minute until the conditions are removed.

The BCM will provide an audible chime based on the class II message received from the SDM if the driver's seat belt is not buckled when the ignition is turned to run or crank. The chime rate for this feature is 50 chimes per minute.

The BCM will provide an audible chime for park brake when the park brake is applied and the vehicle speed is higher that 3 mph. The chime rate for this feature is 200 chimes per minute.

The body control module (BCM) will provide 4 chimes for each telltale activation per ignition cycle, at a rate of 150 or 200 chimes per minute. The chimes are limited to 1 chime event per telltale for each ignition cycle. The power up telltale function will not activate the telltale chime function. If the telltale becomes active during a cycle then the chime will sound.

The following telltales will activate the chime function:

Door locking/unlocking by remote keyless entry (RKE), or driver/all door-lock switches, is controlled through the BCM.

When a driver door unlock has been requested, the BCM switches from circuit 1391 to battery voltage. This energizes the driver door-unlock relay which supplies power to the driver door-lock motor. Grounding is achieved through the closed contacts of the all-door-lock relay. Grounding is also achieved through the windings of the all-door-lock motors and the all-door-unlock relay.

When an all-door lock has been requested, the BCM switches from circuit 194 to battery voltage. This energizes the all-door-unlock relay which supplies power to all door-lock motors. Grounding is achieved through the closed contacts of the door-unlock relay.

When an all-door lock has been requested, the BCM switches circuit 195 to battery voltage. This energizes the all-door-lock relay which supplies power to all-door lock motors. Grounding is achieved through the closed contacts of the driver door-unlock relay and the all-door-unlock relay.

Lock/unlock power application is limited by the BCM to 7 seconds to protect the lock motors.

The trunk/liftgate release if controlled by the body control module (BCM) circuit 382 providing battery voltage to the release solenoid. The BCM limits the amount of time the solenoid can be activated to 9 seconds to prevent damage to the solenoid. Reactivation may not be allowed for as much as 30 seconds.

Release of the decklid/liftgate can be initiated by either the transmitter or the decklid/liftgate release switch. Activating the decklid/liftgate release switch provides battery voltage to circuit 56. Because the remote keyless entry is an internal function of the BCM, no additional external wiring is necessary for transmitter input to the BCM. Decklid/liftgate release is not allowed by the BCM when vehicle speed is detected. The BCM receives vehicle speed serial data from the engine controller. The trunk release, in sedan vehicles, has a valet switch to limit trunk access.

The BCM also monitors the state of the decklid/liftgate. When circuit 744 is grounded by the ajar switch, the BCM will alert the driver that the decklid/liftgate is ajar by turning On the ajar telltale.

The BCM will set the DTC B3109 -- Keyless Entry Transmitter Low Battery -- when the transmitter battery voltage is below 2.5 volts. Nominal transmitter battery voltage is 3.0 volts.

Under low brake fluid conditions, the brake fluid switch closes, When closed, the brake fluid switch grounds circuit 333. The BCM responds by sending a serial data message to the instrument panel cluster (IPC) to turn on the brake telltale.

When the engine is at the proper level, the low coolant switch is closed. When in this condition, battery voltage is applied to the low coolant circuit 1478 input of the BCM.

When coolant is below the proper level, the low coolant switch opens. Because no voltage is applied to circuit 1478, the BCM responds by sending a serial data message to the instrument panel cluster to turn On the low coolant telltale.

The BCM has an internal timer which will not turn On the low coolant telltale, unless the coolant level is low for greater than 30 seconds. The timer avoids coolant sloshing, falsely turning on the low coolant telltale.

The change oil soon telltale is reset by pressing the oil life reset push-button switch. This switch is located in the underhood fuse block. Pressing this switch grounds circuit 1579. When grounded, the BCM requests the engine controller to perform an oil life reset. When reset is complete, the BCM will turn off the change engine oil telltale.

The BCM receives fuel level data from the ECM for L81 over CAN and from the PCM for L61 over Class II. The BCM calculates the data and sends the result to the cluster, to control fuel gage deflection.

The BCM calculates vehicle mileage from rolling-count data sent to the BCM by CAN message from the ECM on L81, and by Class II message from the PCM on L61 vehicles. The BCM sends the mileage data to the cluster over serial data to display the vehicle mileage.

Follow the Saturn Service Stall reprogramming for the BCM. If unable to communicate with the original BCM, the last value displayed by the cluster must be entered into the new BCM with the Saturn Service Stall during reprogramming.

All telltales in the instrument panel cluster are controlled by the body control module (BCM) with the following exceptions. The air bag and seat-belt telltales are controlled by the sensing and diagnostic module (SDM) via the serial data link. The right and left turn signal telltales are directly wired to the instrument panel cluster.

The following table gives the information source for each telltale:

The instrument panel gages are controlled by the body control module (BCM) via the serial data link to the instrument panel cluster (IPC).

The following table gives the information source for each gage:

The brake transaxle shift interlock (BTSI) solenoid is energized by the BCM switching circuit 816 to ground. When energized, the BTSI solenoid will allow shifting from PARK. A condition for shifting from PARK is that the foot brake must be applied. The BCM receives this information over the serial data link from the engine controller.

The BCM also monitors ignition 1 circuit 339 and ignition 2 circuit 743 to determine if the ignition switch is in the RUN or the ACC position.

Standard HVAC

When the rear defrost input circuit 292 to the BCM is momentarily switched to ground (as when the rear defrost switch is pressed), the BCM will respond by grounding circuit 193, the coil of the rear defrost relay.

This action energizes the rear defrost relay, providing power to circuit 293 -- rear defrost heater elements, circuit 683, heated mirror relay coil and circuit 683 and the rear defrost LED telltale. Momentarily switching circuit 292 to ground again will result in the BCM turning the rear defrost relay Off.

Automatic Climate Control

The request for rear defrost is received by the BCM over serial data (class II). The BCM will energize the relay which sends voltage to the rear defrost grid.

The first time in an ignition cycle, that the rear defrost is activated, the rear defrost will remain On for 15 minutes or until the ignition switch is turned OFF. If rear defrost is activated again during the same ignition cycle, rear defrost will remain on for 7.5 minutes or until the ignition switch is turned OFF.

The automatic climate control system controls the heating, cooling and ventilation in the vehicle. The system is made up of : the HVAC control module, the passenger compartment temperature sensor, the outside temperature sensor, the solar-load sensor and the body control module. The HVAC control module uses the information from the sensors to adjust the temperature in the vehicle to suit the desired settings.

Standard HVAC

The A/C request is made by the HVAC control head, supplying voltage to circuit 66 to the BCM. The BCM will then request over the serial data link to the engine controller to operate the compressor. The BCM provides evaporator freeze protection by monitoring engine speed and ambient temperature.

Automatic Climate Control

The ACC system will request air compressor over serial data from the ACC module to the BCM. The BCM will send the request on to the PCM or ECM, if the request is valid.

Display dimming is controlled by the BCM based on input received from the dimming potentiometer. The dimming potentiometer is connected between circuit 1359 and circuit 1381. The BCM monitors these inputs and provides a pulse width modulated (PWM) output at circuit 8 to operate the display lamps.

The BCM compares the state of park-lamp circuit 9, to the high-beam headlamp circuit  1200, and the low-beam headlamp circuit 1201.

If the park-lamp circuit is grounded/open and either the low-beam circuit is at the battery voltage, or the high-beam circuit is grounded, the DTC B2662 -- Parklamp Switch Circuit Malfunction -- will set.

The body control module (BCM) monitors circuit 79 to determine if the headlamp (park lamp) switch is active or inactive. The automatic lighting control (ALC) system will be inactive if the headlamp/parklamp switch is active. The headlamp relay is commanded on by the BCM through circuit 352. The BCM also monitors circuit 352 for feedback when the headlamp relay is commanded. The system uses light sensor circuit 1137 to switch the ALC on after dark.

Daytime running lamps (DRL) are controlled by the BCM based on input from the high-beam headlamp circuit 1200, the low-beam headlamp circuit 1201, the parking-brake circuit 1134 and the ignition switch state.

When DRL operation is desired, the BCM switches circuit 592 to ground. This action energizes the DRL relay. When energized, the DRL relay operates the left high-beam headlamp and the right high-beam headlamp as a series circuit (one-half of the battery voltage across each high beam headlamp).

When DRL operation is not desired, the BCM does not provide ground for the DRL relay. When not energized (as when the high-beam headlamps are desired) the DRL relay operates the right and the left high-beam headlamps as a parallel circuit (full battery voltage across each high-beam headlamp).

For DRL operation, the parking brake must be fully released, the ignition switch must be in the RUN position and the headlamp switch must be in the Off position. Under normal operating conditions, the feedback voltage to the BCM measured at circuit 1200 is (see chart below):

Dome and rear reading lamp operation is through the body control module (BCM) providing ground to circuit 156. When manually operated by their respective local switches, the dome and rear reading lamps are grounded through circuit 450 and the right body ground splice pack.

Battery rundown protection (inadvertent power) is controlled by the BCM for all devices powered by circuit 1732. The devices include the glove compartment lamp, rear dome lamps, cargo lamp, map lamps, reading lamps, sunshade mirror lamps and courtesy lamps.

Should any device be On, the BCM will turn the inadvertent power Off after 20 minutes to conserve battery energy, if there has not been an ignition switch transition to RUN or START, an RKE LOCK or UNLOCK, a decklid/liftgate operation or a driver/passenger door open/close. Inadvertent power shutoff is disabled in the ignition, in RUN or START.

Important: To prevent battery rundown on newly delivered vehicles, inadvertent power is limited to 3 minutes until the vehicle mileage exceeds 15 miles.

The passlock sensor is powered by circuit 812. The passlock sensor is grounded by circuit 1057. Passlock sensor data is supplied to the BCM by circuit 1836.

The passlock sensor data supplied to the BCM is in the form of V-codes. When the proper ignition key is turned in the ignition switch, the correct V-code is supplied to the BCM. The BCM responds by sending a serial data password to the engine controller allowing the engine to run.

The security resister is bypassed under a tamper condition (possible external magnet applied to the sensor). In this mode, a specific V-code is supplied to the BCM. The vehicle will not start in this mode.

When the ignition key is seated in the ignition switch, the key-in-ignition switch contacts close grounding circuit 80. The BCM monitors the state of the key-in-ignition switch, the state of the ignition switch (OFF, ACC or RUN) and the driver's door to control the key-in-ignition chime.

The BCM controls the operation of the horns for the security system and the remote keyless entry (RKE) functions. Circuit 28 is grounded by the BCM when horn operation is desired. Normal operation of the horn is performed by the horn switch grounding the horn relay and is not controlled by the BCM.

There is a 30 second delay prior to setting the DTC B2752 -- Horn Relay Coil Circuit Low -- for grounded conditions. It is possible to set the DTC B2752 if the horn is operated by the horn switch for greater than 30 seconds.

When the traction control system is in the On state, the traction control light-emitting diode (LED) request from the electronic brake traction control module (EBTCM) to the BCM circuit 832 is at battery voltage. In response, the BCM grounds circuit 1660. This action turns on the traction control LED indicating to the driver the traction control system is able to react to slippery conditions.

When the traction control system is in the Off state, the traction control LED request from the EBTCM to the BCM circuit 832 is switched to ground. In response, the BCM switches OFF the traction control LED indicating to the driver the traction control system has been disabled.

The intermittent wiper delay switch is a voltage divider connected across BCM inputs circuit 113 and circuit 96. The wiper relay is energized by the BCM switching circuit 1445-to-ground depending on the delay switch position.

The intermittent wiper delay switch has 3 switch positions:

The body control module (BCM) monitors the front washer motor circuit 228. When a front windshield wash is requested for more than 2 minutes, circuit 228 at battery voltage, the BCM will turn OFF the front wiper motor if the front wiper is NOT requested by the wiper switch.

Power for the front washer motor (and rear washer motor when equipped) is supplied through the front wiper fuse and washer switch. Grounding for the front washer motor is through circuit 550 or through the OFF position of the rear washer motor switch (when equipped).

The BCM monitors the rear washer motor circuit 392. When a rear windshield wash is requested for more than 2 minutes, circuit 392 at battery voltage, the BCM will turn Off the rear wiper motor if the rear wiper is NOT requested by the wiper switch.

Power for the rear washer motor is supplied through the front wiper fuse and rear washer switch. Grounding for the rear washer motor is through the OFF position of the front washer motor switch.

When intermittent or mist operation of the windshield wiper is selected, the battery voltage from the wiper switch is applied to the front wiper input of the BCM. The BCM responds by switching circuit 1445-to-ground. This action energizes the front wiper relay, providing low speed operation of the wiper motor during single swipes.

Control of the wiper during continuous LO or HI speed switch settings is directly wired from the wiper switch to the wiper motor and is not under the control of the BCM.

The body control module (BCM provides a notification feature that will: unlock all of the doors if the vehicle is equipped with power door locks, turn on the dome lamp and flash the daytime running lamps (DRLs). The sensing and diagnostic module (SDM) will send the air bag deployed message to the BCM. The BCM will begin the notification event 15 seconds after receiving the message. The BCM will continue flashing the DRLs and keep the dome lamp on until the ignition is turned from on to off, then on again. The notification feature is enabled from the factory on all L-series vehicles.

When operation of the rear wiper is selected, battery voltage from the rear wiper switch is applied to the rear wiper input of the BCM circuit 94. The BCM responds by switching circuit 1445-to-ground. This action energizes the rear wiper input relay, providing power to the rear wiper motor.