Automatic Climate Control

The automatic climate control (ACC) system controls the heating, cooling, and ventilation in the vehicle. The ACC system will request air compressor over serial data from the heating, ventilation, and air conditioning (HVAC) control module to the body control module (BCM). The BCM will send the request on to the powertrain control module (PCM) or engine control module (ECM), if request is valid.

Standard HVAC

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.

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 are enable and disabling 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 doors, then within 500 mS the drivers door will unlock. This feature can be overridden in 2 ways:

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 key in ignition, light ON, occupant restraint (seat belt) and park brake.

Key in Ignition Audible Chime

The ignition key must be seated and rotated before a chime will occur. The BCM will provide an audible chime if the key is left in the ignition in either OFF or Accessory position with the drivers door open. The chime rate for this chime is 150 chimes per minute. The key in ignition chime has a higher priority than the lights ON chime.

Lights On Audible Chime

The BCM will provide an audible chime if the park lights are ON and the drivers door open. In addition one of 2 other conditions exists. The key is out of the ignition or the key is in the ignition at 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.

Occupant Restraint Audible Chime

The BCM will provide an audible chime based on the class 2 message received from the SDM if the drivers 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.

Park Brake Audible Chime

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

Telltale Chimes

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

The following lights will activate the chime function:

The body control module (BCM) monitors circuit 74 to determine if the headlamps (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.

Battery rundown protection, inadvertent power, is controlled by the BCM for all devices powered by circuit 1732. The devices include 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 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, decklid operation or a driver/passenger door open/close. Inadvertent power shutoff is disabled in ignition RUN or START.

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

The body control module (BCM) is pre-programmed with software and calibrations for operation when received from the plant. The requirements for replacement of the module are located in the Saturn Service Stall (SSS) Users Guide. In general, the existing BCM information is read from the controller and stored in SSS until the new BCM is installed. Then the option content, odometer, and other vehicle specific information, from the original BCM is written into the new BCM. If the original controller is unreadable, the option content for the specific vehicle will require input. Refer to Body Control Module (BCM) Programming/RPO Configuration on the procedure for programming a BCM.

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 voltage, circuit 339 and Accessory , circuit 743 to determine if the ignition switch is in the RUN or ACC position.

The class 2 serial data circuit 1807 is used to communicate information between modules, for example the BCM and the engine controller.

Contained in each modules 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 a module, if no other message need to be sent, to let all the other modules on the serial data circuit know the sending module is working correctly.

Each time the ignition is turned ON, all the modules on the class 2 serial data circuit first learn the other modules connected to the class 2 serial 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 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 2 data circuit.

The engine control module (ECM), and the transmission control module (TCM) communicate with each other over the CAN (controller area network) bus circuit 2501 and circuit 2500 (V6 only). The CAN bus is a communication link similar to class 2.

The body control module (BCM) acts as a gateway between the other modules connected to the class 2 serial data circuit 1807 and the ECM, and TCM connected to the CAN bus circuit 2501 and circuit 2500.

State of health (SOH) messages are sent from the ECM, and TCM to the BCM when the ignition is turned ON and during vehicle operation. These messages tell the BCM, the ECM, and the 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 TCM, the BCM sets DTC U2104 - CAN Bus Reset Counter Overrun.

When engine coolant 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 warning light.

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

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 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 high beam headlamps or low beam headlamps (later models) as a series circuit, one-half of 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 high beam headlamps or low beam headlamps (later models) are desired, the DRL relay operates the high beam headlamps or low beam headlamps (later models) as a parallel circuit, full battery voltage across each headlamp.

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

The decklid/liftgate release is 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 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. Decklid 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 the decklid/liftgate is ajar by turning ON the ajar telltale.

The delayed locking feature will activate when a valid lock command is received from a transmitter or a door lock switch (later models) while any door or trunk remains open with the key not in the ignition. The BCM will delay locking the vehicle until all doors and decklid (hatch) are closed. The lock command will execute within 500 mS after all doors and/or decklid transition 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 the 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.

Battery 1 voltage is supplied to the BCM by circuit 2540. Battery 2 voltage is supplied to the BCM by circuit 1640. These inputs are internally monitored by the BCM for proper operating voltage. The proper operating voltage range is from 9-16 volts.

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 there inputs and provides a pulse width modulated (PWM) output at circuit 8 to operate the display lamps.

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.

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 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 unlock has been requested, the BCM switches 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 lock relay. Grounding is also achieved through the winding of the driver door lock motor and the driver 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 all-door unlock relay.

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

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, DTC B1000 - ECU Malfunction sets. The checksum is the contents of each memory location in EEPROM added together.

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

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

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

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.

When intermittent or mist operation of the windshield wiper is selected, 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 direct wired from the wiper switch to the wiper motor and is not under the control of the BCM.

The BCM receives fuel level data from the ECM (L81) over CAN or PCM (L61) over class 2. The BCM calculates the data and sends the result to the instrument cluster to control the fuel gage deflection. The scan tool supports a display for fuel gage position.

Ground for the BCM is by circuit 550 through the instrument panel (I/P) ground splice pack.

The BCM controls the operation of the horns for the security system and 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 DTC B2752 - Horn Relay Coil Circuit Low for grounded circuit conditions. It is possible to set DTC B2752 if the horn is operated by the horn switch for greater than 30 seconds.

There are several lights/gages in the I/P cluster that can be controlled by the BCM. The BCM will send a class 2 message to the I/P cluster when certain DTCs set in the BCM. Refer to the specific BCM DTC in order to determine if an indicator was turned ON by the BCM. For a description on all I/P cluster lights/gages, refer to Indicator/Warning Message Description and Operation in Instrument Panel, Gages and Console.

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 delay switch position.

The intermittent wiper delay switch has 3  switch positions:

Refer to Wiper/Washer System Description and Operation in Wiper/Washer Systems for the timing of each delay position.

When the ignition key is seated and rotated 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 drivers door to control the key-in-ignition chime.

The BCM will fail 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 system warning light.

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 lights (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. The notification feature is enabled from the factory on all vehicles.

The BCM calculates vehicle mileage from rolling count data sent to the BCM by a CAN message from the ECM (L81) or a class 2 message from the PCM (L61). The BCM sends the mileage data to the cluster over serial data to display the vehicle mileage. The actual mileage is located in the BCM. All calculations for odometer are performed in the BCM.

The change oil soon light is reset by depressing 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 completed, the BCM will turn OFF the change engine oil light.

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 programming procedure is completed, DTC B1001--Option Configuration Error will set.

When the park brake input circuit 1134 to the BCM is grounded, as when the parking brake is applied, the BCM will turn ON the brake light in the I/P cluster by sending a serial data message to the instrument panel cluster (IPC).

If the vehicle is moving at greater than 3 mph (5 km/h) and the park brake input to the BCM is grounded, the BCM will sound the warning chime to notify the driver the parking brake is applied. DTC B0005--Park Brake Switch Circuit Low will set under these conditions.

The BCM compares the state of the park lamp circuit 74 to the high beam headlamp circuit 1200 and the low beam headlamp circuit 1201.

The BCM monitors ignition 1 voltage circuit 339, accessory 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 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 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 relay, providing power to the rear wiper motor.

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 or voltage 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 resistor is bypassed under a tamper condition, possible external magnet applied to sensor. In this mode, a specific V-Code is supplied to the BCM. The vehicle will not start in this mode.

When the traction control system is in the ON state, the traction control light emitting diode (LED) request from the electronic brake control module (EBCM) 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 EBCM 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.