Computer/integrating Systems Cadillac XLR I

Fastener Tightening Specifications

Fastener Tightening Specifications

Computer/Integrating Systems Schematic Icons Icon Icon Definition CAUTION: When performing service on or near the SIR components or the SIR wiring, the SIR system must be disabled. Refer to SIR Disabling and Enabling. Failure to observe the correct procedure could cause deployment of the SIR components, personal injury, or unnecessary SIR system repairs. IMPORTANT: Twisted-pair wires provide an effective shield that helps protect sensitive electronic components from electrical interference. In order to prevent electrical interference from degrading the performance of the connected components, you must maintain the proper specification when making any repairs to the twisted-pair wires shown : The wires must be twisted a minimum of 9 turns per 31 cm (12 in) as measured anywhere along the length of the wires. The outside diameter of the twisted wires must not exceed 6.0 mm (0.25 in)

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Computer/Integrating Systems Connector End Views

Body Control Module (BCM) C1

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Computer/Integrating Systems Connector End Views

Body Control Module (BCM) C2

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Computer/Integrating Systems Connector End Views

Body Control Module (BCM) C3

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Computer/Integrating Systems Connector End Views

Body Control Module (BCM) C4

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Computer/Integrating Systems Connector End Views

Data Link Connector (DLC)

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Computer/Integrating Systems Connector End Views

Splice Pack SP205

Splice Pack SP208

Computer/Integrating Systems Connector End Views

Splice Pack SP208

Diagnostic Code Index

DIAGNOSTIC CODE INDEX

Scan Tool Output Controls

BCM

RCDLR

Scan Tool Data List

BCM Data

RCDLR Data

Circuit Description

The ignition mode switch has 3 LEDs that indicate the vehicle power mode. When the vehicle is in the Off mode, the Off LED may illuminate. Pressing the lower button of the ignition mode switch, the vehicle enters the accessory mode and ACC LED will illuminate. Keeping the lower button pressed for about 5-6 seconds, the vehicle enters run mode with the engine off and the START LED will illuminate. All these LEDs have the voltage supplied from the body control module (BCM) through the ignition mode switch supply voltage circuit. The ground path for each LED is controlled by the BCM.

DTC Descriptors

This diagnostic procedure supports the following DTCs

1. DTC B0976 Off Indicator Control Circuit
2. DTC B0977 Start Indicator Control Circuit
3. DTC B0978 Accessory Indicator Control Circuit

DTC B0976, B0977, or B0978

Conditions for Running the DTC

Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.

Conditions for Setting the DTC

B0976 01

1. The BCM detects a short to battery in the off indicator control circuit.
2. The above condition exists for more than 5 seconds.

B0977-B0978 01

1. The BCM detects a short to battery in the respective indicator control circuit, when the output is active.
2. The above condition exists for more than 1 second.

B0976-B0978 06

1. The BCM detects an open or short to ground in the respective indicator control circuit, when the output is inactive.
2. The above condition exists for more than 1 second.

B0976-B0978 01

The BCM disables the respective output until the next ignition cycle.

Conditions for Clearing the DTC

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. 3: If more than one DTC were retrieved, the fault condition is common for all circuits.
2. 7: A LED that illuminates, assures that the fault is not internal to the ignition mode switch.
3. 8: A B0976 requires vehicle in OFF mode, a B0977 requires ignition ON with the engine OFF and a B0978 requires vehicle in accessory mode.

DTC B0976, B0977, or B0978

The internal fault detection is handled inside the control module. No external circuits are involved.

DTC Descriptor

This diagnostic procedure supports the following DTC

DTC B1000 Electronic Control Unit (ECU) Performance

DTC B1000

The module runs the program to detect an internal fault when power up is commanded. The only requirements are voltage and ground. This program runs even if the voltage is out of the valid operating range.

The module has detected an internal malfunction.

Action Taken When the DTC Sets

The module refuses all additional inputs.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Diagnostic Aids

1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and history DTC, replace the module.

DTC B1000

The body control module (BCM) stores the last 4 digits of the sensing and diagnostic module (SDM) part number, information also called restraints ID. After the BCM is reprogrammed the restraints ID is set to zero. A restraints ID relearn must be performed for the BCM. For more information on this procedure refer to Body Control Module (BCM) Programming/RPO Configuration .

This diagnostic procedure supports the following DTC

DTC B1001 Option Configuration Error

DTC B1001

Battery voltage is between 9-16 volts and data link communications operate normally.

The restraints ID value stored in the BCM memory is zero.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

DTC B1001

The internal fault detection is handled inside the control module. No external circuits are involved.

This diagnostic procedure supports the following DTC

DTC B1004 keep alive memory (KAM) Reset

The module microprocessor must be active/awake.

This DTC indicates the KAM in the module has been reset. It is a normal occurrence when battery positive voltage or ground is removed from the module, such as a battery disconnect.

The microprocessor reverts back to the base programmed critical operating data until new data is learned and stored in KAM.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and history DTC, replace the module.

DTC B1004

As part of normal data processing, the module performs a data programming check on its writes to the electrically erasable read only memory (EEPROM). The EEPROM write error detection is handled inside the control module. No external circuits are involved.

This diagnostic procedure supports the following DTC

DTC B1007 EEPROM Write Error

The module runs the program to detect an EEPROM write error. The only requirements are battery positive voltage and ground. This program runs even if the battery positive voltage is out of the valid operating range.

The module writes information to a data block in the EEPROM. The module then reads the data and compares it to what was sent to the data block. If the data does not match after 3 consecutive attempts, the module sets the DTC.

The module writes to another area of the EEPROM, this becomes the new permanent area to store the data. The data location is allowed to change until all of the available EEPROM is used. If a DTC B1004 is also set, the module reverts to base operation values programmed for those blocks of data that have failed. The blocks of data that have not failed the checksum test are not affected.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and history DTC, replace the module.

DTC B1007

The electrically erasable programmable read-only memory (EEPROM) check sum error detection is handled inside the control module. No external circuits are involved.

This diagnostic procedure supports the following DTC

DTC B1009 EEPROM Checksum Mismatch

The module runs the program to detect an EEPROM checksum error after each wake-up. The only requirements are battery positive voltage and ground. This program runs even if the voltage is out of the valid operating range.

The module retains an inverse copy of the digital value stored in certain blocks of memory in the EEPROM. The module then reads the information from those certain blocks and adds the stored inverse value to the current value. If they do not equal 0, the module sets the DTC.

The module reverts to base operation values programed for those blocks of data that have failed the check sum test. The blocks of data that have not failed the check sum test are not affected.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and history DTC, replace the module.

DTC B1009

This test checks the validity of the module FLASH memory calibration values. Error detection is performed inside the control module. No external circuits are involved.

This diagnostic procedure supports the following DTC

DTC B1013 Calibration Read Only Memory (ROM) Checksum Error

The module runs the program to detect a FLASH calibration error after each wake-up. The only requirements are battery positive voltage and ground.

The module retains a copy of the FLASH calibration checksum reference value in the FLASH memory. During wake-up the module shall compute the FLASH calibration value and compare it to the FLASH calibration checksum reference value. If the 2 values do not match the module sets this DTC.

The module may have limited functional operation depending on the severity of the FLASH calibration corruption. The module physical operation will allow for the module to be reprogrammed to correct the malfunction.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

The following are most likely cause for this DTC being set

1. Incorrect files downloaded to the module
2. A module installed in the vehicle without the reprogramming procedure having been performed.

DTC B1013

This test checks the validity of the module FLASH memory application values. Error detection is performed inside the control module. No external circuits are involved.

This diagnostic procedure supports the following DTC

DTC B1014 Program Read Only Memory (ROM) Checksum Error

The module runs the program to detect a FLASH application error after each wake-up. The only requirements are battery positive voltage and ground.

The module retains a copy of the FLASH application checksum reference value in the FLASH memory. During wake-up the module shall compute the FLASH application value and compare it to the FLASH application checksum reference value. If the 2 values do not match the module sets this DTC.

The module will enter boot mode when this DTC sets. In boot mode, only the program FLASH memory function will be available.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

The following are most likely cause for this DTC being set

1. Incorrect files downloaded to the module
2. A module installed in the vehicle without the reprogramming procedure having been performed.

DTC B1014

The remote control door lock receiver (RCDLR) provides an high side drive output for the ignition 1 voltage circuit. The ignition 1 voltage circuit controls the Run/Crank relay when the backup power mode is enabled.

This diagnostic procedure supports the following DTC

DTC B1370 Device Ignition 1 (ON and START) Circuit

Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.

1. The RCDLR detects a short to ground in the ignition 1 voltage circuit when the output is active.
2. The RCDLR detects a short to battery or an open in the ignition 1 voltage circuit when the output is inactive.
3. Any of the condition above must be present for more than 0.375 seconds.

The RCDLR disables the output for the current ignition cycle when a short to ground is detected.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

DTC B1370

The body control module (BCM) is the power mode master and the remote control door lock receiver (RCDLR) is the backup power mode master. Both modules receive information regarding ignition mode switch position from the ignition mode switch. The ignition mode switch will be monitored only with battery voltage at or above 7 volts to prevent invalid input readings during low voltages encountered during vehicle cranking.

Four modes are discernible

1. Inactive
2. Start active
3. Off active
4. Short detect

If the BCM detects a change in the ignition mode switch data, sends a class 2 message to RCDLR requiring authentication for that change.

This diagnostic procedure supports the following DTC

DTC B1440 Power Mode Master Input Circuits Mismatch

The only requirements are voltage and ground.

The RCDLR sets this code if any of the following conditions occur

1. The RCDLR mode data input is active for more than 60 seconds, without seeing the corresponding message from the BCM.
2. The RCDLR detects a short to ground on its mode data input circuit, for more than 60 seconds.

One of the following scenarios may take place

1. If the RCDLR senses a change on its ignition mode data input two times in a row, but does not receive the corresponding message from the BCM, the RCDLR will enable the backup power mode. The backup power mode will be changed accordingly to signal sensed.
2. If the RCDLR receives a message from the BCM, indicating that a switch has been pressed, without sensing the change itself, backup power moding will be disabled for the current ignition cycle.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

The setting of this DTC can be caused by various failures

1. The RCDLR malfunction
2. The BCM malfunction
3. The ignition mode switch malfunction
4. The ignition mode data input and ground circuits for either the RCDLR or the BCM

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step checks for a proper reading of the ignition mode switch by the BCM.
2. 11: This step checks for a proper reading of the ignition mode switch by the RCDLR.

DTC B1440

The body control module (BCM) provides an accessory voltage output, enabled in Run and Accessory power modes. The accessory voltage circuit provides power for the engine control module (ECM), the transmission control module (TCM), and the traffic information receiver (TIR) module, if equipped. The accessory voltage circuit also provides power to the Wiper Run/Acc relay.

This diagnostic procedure supports the following DTC

DTC B1451 Accessory Power Circuit

DTC B1451

Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.

B1451 02

1. The BCM detects a short to ground in the accessory power circuit when the output is active.
2. The condition above must be present for more than 5 seconds.

B1451 05

1. The BCM detects a short to battery or an open in the accessory power circuit when the output is inactive.
2. The condition above must be present for more than one second.

B1451 02

The BCM will disable the accessory power output until the next ignition cycle.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

If the DTC B1451 02 or B1451 05 is a history DTC, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections .

The following conditions may cause DTC to occur

1. A short to ground, a short to battery or an open in the accessory power circuit
2. A fault in one of the following modules that shorts the circuit to ground or battery: ECM TCM TIR, if equipped
3. An internal Wiper Run/Acc relay fault
4. An internal BCM fault

DTC B1451

The ignition mode switch has 3 LEDs that indicate the vehicle power mode. All these LEDs have the voltage supplied from the body control module (BCM) through the ignition mode switch supply voltage circuit. The ground path for each LED is controlled by the BCM.

This diagnostic procedure supports the following DTC

DTC B2625 Display Dimming Pulse Width Modulation (PWM) Output Circuit

DTC B2625

Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.

1. The BCM detects a short to ground in ignition mode switch supply voltage circuit.
2. The above condition is present for at least 1 second.

1. The BCM stores the respective DTC in memory.
2. None of the LEDs indicators will work.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

If the DTC is history only, the fault may be intermittent. Refer to Testing for Intermittent Conditions and Poor Connections . The following conditions may cause an intermittent malfunction to occur

1. An intermittent short to ground in the ignition mode switch supply voltage circuit
2. An intermittent short to ground internal to the ignition mode switch
3. An intermittent short to ground internal to the BCM

DTC B2625

Modules connected to the GMLAN serial data circuit monitor for serial data communications on the GMLAN network during normal vehicle operation. Operating information and commands are exchanged among the modules. Each module on GMLAN network maintains a transmit error counter (TEC) and a receive error counter (REC). The counter values increase with detected errors and will decrease with error-free messages. If the TEC value exceeds 255 the controller removes itself from the network and a DTC U0001 will be set.

This diagnostic procedure supports the following DTC

DTC U0001 High Speed CAN Communication Bus

This vehicle has DTCs which include DTC Symptoms. For more information on DTC Symptoms, refer to Symptoms - Vehicle in Vehicle DTC Information.

DTC U0001

Conditions for Running the DTCs

1. Voltage supplied to the module is in the normal operating voltage range.
2. The vehicle power mode requires serial data communication to occur.

A certain number of no valid transmitted messages on the GMLAN serial data circuits are detected by the module.

Action Taken When the DTCs Sets

1. The module suspends all message transmission.
2. The module uses default values for all parameters received on the GMLAN serial data circuits.
3. The module inhibits the setting of all other GMLAN communication DTCs.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. This DTC cannot be retrieved with a current status. Diagnosis of current DTC is accomplished via the symptom, Scan Tool Does Not Communicate with GMLAN Device. Refer to «Scan Tool Does Not Communicate with High Speed GMLAN Device»(/cadillac/xlr/i-2003-2009/remont/communication-devices/#computerintegrating-systems__scan-tool-does-not-communicate-with) .
2. An intermittent condition is likely to be caused by a short on the GMLAN serial data circuits. Use the Scan Tool Does Not Communicate with GMLAN Device procedure in order to isolate an intermittent condition. Refer to «Scan Tool Does Not Communicate with High Speed GMLAN Device»(/cadillac/xlr/i-2003-2009/remont/communication-devices/#computerintegrating-systems__scan-tool-does-not-communicate-with) .

The GMLAN serial data circuits are controller area network (CAN) high and/or low speed serial data buses used to communicate information between the control modules. Typical data transmission speeds must be high enough to ensure that a required real-time response is maintained. There are two different types of GMLAN serial data circuits, the High speed 2-wire circuit and Low speed single wire circuit. Refer to Data Link Communications Description and Operation for the complete description of the buses used on this vehicle. The GMLAN serial data circuits also communicate directly to the data link connector (DLC). Messages are interpreted by the externally connected CANdi module which acts as a transceiver for the scan tool.

Modules connected to the GMLAN serial data circuits monitor communications during normal vehicle operation, where operation information is exchanged among the modules. All the modules on the GMLAN networks, maintain a transmit error counter (TEC) and a receive error counter (REC). The counter values increase with detected errors and will decrease with error-free messages. If the TEC value exceeds 255, the controller removes itself from the network and DTC U0073 will result.

This diagnostic procedure supports the following DTC

DTC U0073 Controller Area Network (CAN) Bus Communication

1. Supply voltage to the modules are in the normal operating range.
2. The vehicle is in the RUN power mode.

The module setting the DTC has attempted to establish communications on the GMLAN circuits for more than 7 times.

1. The module suspends all message transmission.
2. The module uses default values for all parameters received on the serial data circuits.
3. The module inhibits the setting of all other communication DTCs.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. This DTC cannot be retrieved with a current status. Diagnosis of a current DTC is accomplished via the symptom, Scan Tool Does Not Communicate with High and/or Low Speed GMLAN Device. Refer to «Data Link References»(/cadillac/xlr/i-2003-2009/remont/communication-devices/#computerintegrating-systems__data-link-references) for the correct procedure for the specific module(s) and the busses they use to communicate.
2. An intermittent condition is likely to be caused by a short on the GMLAN serial data circuits. Use the Scan Tool Does Not Communicate with High and/or Low Speed GMLAN Device procedure in order to isolate an intermittent condition. Refer to «Data Link References»(/cadillac/xlr/i-2003-2009/remont/communication-devices/#computerintegrating-systems__data-link-references) for the correct procedure for the specific modules.

Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised; also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module.

This diagnostic procedure supports the following DTCs

1. DTC U0100 Lost Communication With Engine Control Module (ECM)
2. DTC U0101 Lost Communication With Transmission Control Module (TCM)
3. DTC U0104 Lost Communication With Distance Sensing and Cruise Control (DSCC) Module
4. DTC U0121 Lost Communication With Electronic Brake Control Module (EBCM)
5. DTC U0140 Lost Communication With Body Control Module (BCM)

DTC U0100-U0299

1. Voltage supplied to the modules is in the normal operating voltage range.
2. The vehicle power mode requires serial data communication to occur.
3. The DTC U0001 does not have a current status.

A supervised periodic message that includes the transmitter module availability has not been received.

The module uses a default value for the missing parameter.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. A poor connection at the inoperative module may cause this code to set.
2. An improperly powered module may cause this code to set.

The numbers below refer to the step numbers on the diagnostic table.

1. 3: The scan tool communicate with OnStar® via class 2, so for high speed GMLAN data link diagnostic the OnStar® will not be considered.
2. 15: The module which was not communicating due to an open in the GMLAN serial data circuits may have set Loss of Communication DTCs for those modules that it was monitoring.
3. 17: The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.

DTC U0100-U0299

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State of Health monitoring. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. When a module does not associate an identification number with at least one critical parameter within 5-10 seconds of beginning serial data communication, DTC U1000 or U1255 is set. When more than one critical parameter does not have an identification number associated with it, the DTC will only be reported once.

The following modules communicate on the class 2 serial data circuit

1. The body control module (BCM)
2. The communication interface module (OnStar®)
3. The CD changer (CDX)
4. The digital radio receiver (DRR)
5. The driver door module (DDM)
6. The driver door switch (DDS)
7. The driver position module (DPM)
8. The fold top controller (FTC)
9. The head up display (HUD)
10. The HVAC control module
11. The inflatable restraint sensing and diagnostic module (SDM)
12. The instrument panel cluster (IPC)
13. The passenger door module (PDM)
14. The radio
15. The remote control door lock receiver (RCDLR)
16. The steering column lock control module (SCLCM)

The BCM emulates all devices that are on high speed GMLAN serial data circuits to the modules on class 2 serial data circuit. The BCM transmits multiple Node Alive messages using source IDs that correspond to each of the GMLAN nodes. This is in addition to the BCM behaving itself as a real node. The following module communicate on high speed GMLAN serial data circuits and are emulated by BCM on class 2 serial data circuit

1. The distance sensing cruise control (DSCC) module
2. The electronic brake control module (EBCM)
3. The electronic suspension control module (ESC)
4. The engine control module (ECM)
5. The transmission control module (TCM)

This diagnostic procedure supports the following DTCs

DTC U1000 or U1255 Class 2 Data Link

DTC U1000 and U1255

1. Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.
2. DTCs U1300, U1301 or U1305 do not have a current status.
3. The vehicle power mode requires serial data communication to occur.

A message containing a critical operating parameter has not been received within the last 5-10 seconds after establishing class 2 serial data communication.

The module uses a default value for the missing parameter.

When a malfunction such as an open fuse to a module occurs while modules are communicating, a DTC U1001-1254 Loss of XXX Communications is set current. When the modules stop communicating the current DTC U1001-1254 Loss of XXX Communications is cleared but the history DTC remains. When the modules begin to communicate again, the module with the open fuse will not be learned by the other modules so U1000 or U1255 is set current by the other modules. If the malfunction occurs when the modules are not communicating, only U1000 or U1255 is set.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: A DTC U1001-U1254 Lost Communications with XXX with a history status may indicate the cause of U1000 or U1255. A non-communicating GMLAN module can cause the DTC setting, besides other DTC in the range of U2105-U2175 or U0100-U0299.
2. 3: The modules not communicating are the likely cause of U1000 or U1255. The modules that are available on the class 2 serial data circuit are listed in the Circuit Description.
3. 8: The module which was not communicating due to a poor connection to the class 2 serial data circuit may have set DTC U1001-U1254 Lost Communications with XXX for those modules that it was monitoring.
4. 10: The modules which can communicate indicate the module which cannot communicate. You must clear the serial data communication DTCs from these modules to avoid future misdiagnosis.
5. 12: If all modules are communicating, the module which set U1000 or U1255 may have done so due to some other condition.
6. 13: If all modules are communicating, the module which set U1000 or U1255 is the likely cause of the malfunction.

DTC U1000 and U1255

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State of Health (SOH) monitoring. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. Once an identification number is learned by a module, it will monitor for that module's Node Alive message. Each module on the class 2 serial data circuit which is powered and performing functions that require detection of a communications malfunction is required to send a Node Alive message every 2 seconds. When no message is detected from a learned identification number for 5-10 seconds, a DTC U1xxx where xxx is equal to the 3-digit identification number is set.

The control module ID number list below provides a method for determining which module is not communicating. A module with a class 2 serial data circuit malfunction or which loses power during the current ignition cycle will have a Loss of Communication DTC set by other modules that depend on information from that failed module. The modules that can communicate will set a DTC indicating the module that cannot communicate. The following modules communicate on class 2 serial data circuit

DTC U1001-U1254

The body control module (BCM) emulates some devices that are on high speed GMLAN serial data circuit to the modules on class 2 serial data circuit. The BCM transmits multiple Node Alive messages using source IDs that correspond to each of those high speed GMLAN nodes. This is in addition to the BCM behaving itself as a real node. The following module communicate on high speed GMLAN serial data circuit and are emulated by BCM on class 2 serial data circuit

DTC U1001-U1254

When more than one Loss of Communication DTC is set in either one module or in several modules, diagnose the DTCs in the following order

1. Current DTCs before history DTCs unless told otherwise in the diagnostic table.
2. The DTC which is reported the most times.
3. From the lowest number DTC to the highest number DTC.

This diagnostic procedure supports the DTCs U1xxx, where xxx is equal to the 3-digit identification number from the tables above.

DTC U1001-U1254

1. The following diagnostic trouble codes do not have a current status: U1300 U1301 U1305
2. The vehicle power mode requires serial data communication to occur.

A node alive message has not been received from a module with a learned identification number within the last 5 seconds.

The module uses a default value for the missing parameter.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. An intermittent open between the inoperative module and a star connector may cause these codes.
2. A poor connection at the inoperative module or a star connector may cause these codes.
3. An intermittent open in a star connector may cause these codes.
4. An improperly powered module may cause these codes.
5. An improper communication on the high speed GMLAN serial data circuit may cause these codes.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: A module that does not communicate in high speed GMLAN link may cause the setting of the class 2 DTCs.
2. 3: A module which loses power during an ignition cycle will cause other modules to set lost communication DTCs.
3. 4: A module which loses power during an ignition cycle will cause other modules to set lost communication DTCs.
4. 5: The malfunction is due to an open in the class 2 serial data circuit or an open in the module.
5. 9: The module which was not communicating may have set lost communication DTCs for those modules that it was monitoring.
6. 11: The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.

DTC U1001-U1254

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. In addition to this, Node Alive messages are transmitted by each module on the class 2 serial data circuit about once every 2 seconds. When the module detects one of the following conditions on the class 2 serial data circuit for approximately 3 seconds, the setting of all other class 2 serial communication DTCs is inhibited and a DTC will set.

This diagnostic procedure supports the following DTCs

1. DTC U1300 Class 2 Data Link Low
2. DTC U1301 Class 2 Data Link High
3. DTC U1305 Class 2 Data Link Low or High

DTC U1300, U1301, or U1305

1. Voltage supplied to the module is in the normal operating voltage range.
2. The vehicle power mode requires serial data communication to occur.

Conditions for Setting the DTCs

1. No valid messages are detected on the class 2 serial data circuit.
2. The voltage level detected on the class 2 serial data circuit is in one of the following conditions: High Low
3. The above conditions are met for approximately 3 seconds.

The module uses default values for all parameters received on the class 2 serial data circuit.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

This DTC can be retrieved with a current status from the body control module (BCM) only, because the BCM is the gateway between the class 2 and high speed GMLAN serial data circuits and the BCM diagnostics is performed on high speed GMLAN link. Refer to Data Link Communications Description and Operation for more information about data link communication.

The numbers below refer to the step numbers on the diagnostic table.

1. 7: The class 2 serial data circuit is shorted to voltage or ground. The condition may be due to the wiring or due to a malfunction in one of the modules. When testing the wire for a short, make sure there is not a module connected to the wire being tested. This test isolates the splice pack SP205 serial data circuits.
2. 13: This test isolates the splice pack SP208 serial data circuits.
3. 16: If there are no current DTCs that begin with a "U", the communication malfunction has been repaired.
4. 17: The communication malfunction may have prevented diagnosis of the customer complaint.

DTC U1300, U1301, or U1305

Modules connected to the GMLAN serial data circuit monitor for serial data communications on the GMLAN network during normal vehicle operation. Operating information and commands are exchanged among the modules. Each module on GMLAN network maintains a transmit error counter (TEC) and a receive error counter (REC). The counter values increase with detected errors and will decrease with error-free messages. If the TEC value exceeds 255 the controller removes itself from the network and a DTC U2100 will be set.

This diagnostic procedure supports the following DTC

DTC U2100 High Speed CAN Communication Bus

DTC U2100

1. Voltage supplied to the module is in the normal operating voltage range.
2. The vehicle power mode requires serial data communication to occur.

A certain number of no valid transmitted messages on the GMLAN serial data circuits are detected by the module.

1. The module suspends all message transmission.
2. The module uses default values for all parameters received on the high speed GMLAN serial data circuits.
3. The module inhibits the setting of all other high speed GMLAN communication DTCs.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. This DTC cannot be retrieved with a current status. Diagnosis of current DTC is accomplished via the symptom, Scan Tool Does Not Communicate with high speed GMLAN Device. Refer to «Scan Tool Does Not Communicate with High Speed GMLAN Device»(/cadillac/xlr/i-2003-2009/remont/communication-devices/#computerintegrating-systems__scan-tool-does-not-communicate-with) .
2. An intermittent condition is likely to be caused by a short on the high speed high speed GMLAN serial data circuits. Use the Scan Tool Does Not Communicate with high speed GMLAN Device procedure in order to isolate an intermittent condition. Refer to «Scan Tool Does Not Communicate with High Speed GMLAN Device»(/cadillac/xlr/i-2003-2009/remont/communication-devices/#computerintegrating-systems__scan-tool-does-not-communicate-with) .

Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module.

This diagnostic procedure supports the following DTCs

1. DTC U2105 Lost Communication With Engine Control Module (ECM)
2. DTC U2106 Lost Communication With Transmission Control Module (TCM)
3. DTC U2107 Lost Communication With Body Control Module (BCM)
4. DTC U2108 Lost Communication With Electronic Brake Control Module (EBCM)
5. DTC U2112 Lost Communication With Electronic Suspension Control (ESC) Module
6. DTC U2144 Lost Communication With Distance Sensing and Cruise Control (DSCC) Module

DTC U2105-U2199

1. Voltage supplied to the modules is in the normal operating voltage range.
2. The vehicle power mode requires serial data communication to occur.
3. The DTC U2100 does not have a current status.

A supervised periodic message that includes the transmitter module availability has not been received.

The module uses a default value for the missing parameter.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. A poor connection at the inoperative module may cause this code to set.
2. An improperly powered module may cause this code to set.

The numbers below refer to the step numbers on the diagnostic table

1. 2: If body control module (BCM) detects an open in its class 2 circuit, the remote control door lock (RCDLR) takes control of the run/crank relay.
2. 3: A power moding code needs to be diagnosed first.
3. 5: The scan tool communicate with OnStar® via class 2, so for high speed GMLAN data link diagnostic the OnStar® will not be considered.
4. 17: The module which was not communicating due to an open in the high speed GMLAN serial data circuits may have set Loss of Communication DTCs for those modules that it was monitoring.
5. 19: The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.

DTC U2105-U2199

1. Perform the «Diagnostic System Check - Vehicle»(/cadillac/xlr/i-2003-2009/remont/oem-general-information/#vehicle-dtc-information) in Vehicle DTC Information before using the symptom tables in order to verify that all of the following are true: There are no DTCs set. The control modules can communicate via the serial data links.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to: «Data Link Communications Description and Operation»(/cadillac/xlr/i-2003-2009/remont/communication-devices/#computerintegrating-systems) «Body Control System Description and Operation»(/cadillac/xlr/i-2003-2009/remont/communication-devices/#computerintegrating-systems) «Retained Accessory Power (RAP) Description and Operation»(/cadillac/xlr/i-2003-2009/remont/communication-devices/#computerintegrating-systems)

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the systems. Refer to «Checking Aftermarket Accessories»(/cadillac/xlr/i-2003-2009/remont/body-electrical/#how-to-diagnosis-repair-the-wiring-systems-testing__checking-aftermarket-accessories) in Wiring Systems.
2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «Scan Tool Does Not Power Up»(/cadillac/xlr/i-2003-2009/remont/communication-devices/#computerintegrating-systems)
2. «Scan Tool Does Not Communicate with Class 2 Device»(/cadillac/xlr/i-2003-2009/remont/communication-devices/#computerintegrating-systems)
3. «Scan Tool Does Not Communicate with High Speed GMLAN Device»(/cadillac/xlr/i-2003-2009/remont/communication-devices/#computerintegrating-systems__scan-tool-does-not-communicate-with)
4. «Retained Accessory Power (RAP) On After Timeout»(/cadillac/xlr/i-2003-2009/remont/communication-devices/#computerintegrating-systems__retained-accessory-power-rap-on-after)
5. «Retained Accessory Power (RAP) Inoperative»(/cadillac/xlr/i-2003-2009/remont/communication-devices/#computerintegrating-systems__retained-accessory-power-rap-inoperative)

The data link connector (DLC) is a standardized 16 cavity connector. Connector design and location is dictated by an industry wide standard, and is required to provide the following

1. Scan tool power battery positive voltage at terminal 16
2. Scan tool power ground at terminal 4
3. Common signal ground at terminal 5

The scan tool will power up with the ignition OFF. Some modules however, will not communicate unless the ignition is ON and the power mode master (PMM) module sends the appropriate power mode message.

The number below refers to the step number on the diagnostic table.

1. 4: If the battery positive voltage and ground circuits of the DLC are functioning properly, the malfunction must be due to the scan tool.

Scan Tool Does Not Power Up

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. Connecting a scan tool to the data link connector (DLC) allows communication with the modules for diagnostic purposes.

The numbers below refer to the step numbers on the diagnostic table.

1. 2: A current DTC U1305 may be retrieved only from body control module (BCM).
2. 3: A partial malfunction in the class 2 serial data circuit uses a different procedure from a total malfunction of the class 2 serial data circuit. The following modules communicate on the class 2 serial data circuit. The BCM is diagnosed only through GMLAN serial data circuit. Audio-Amplifier BCM CD changer (CDX) Communication interface module (OnStar®) Digital radio receiver (DRR) Driver door module (DDM) Driver door switch (DDS) Driver position module (DPM) Fold top controller (FTC) Head up display (HUD) HVAC control module Inflatable restraint sensing and diagnostic module (SDM) Instrument panel cluster (IPC) Passenger door module (PDM) Radio Remote control door lock receiver (RCDLR) Steering column lock control module (SCLCM)
3. 7: Data link connector terminals 2 and 5 provide the connection to the class 2 serial data circuit and the signal ground circuit respectively.
4. 9: A poor connection at splice pack SP205 will cause this condition but will not set a DTC.
5. 10: An open in the class 2 serial data circuit between the DLC and splice pack SP205 will prevent the scan tool from communicating with any module on the class 2 network. This condition will not set a DTC.

Scan Tool Does Not Communicate with Class 2 Device

Scan Tool Does Not Communicate with High Speed GMLAN Device

Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications on the high speed GMLAN network during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module detects a bus-off condition a DTC U0001 or U2100 will be set. These DTCs can be retrieved as history only.

The high speed GMLAN serial data bus uses two 120 ohm terminating resistors that are in parallel with the high speed GMLAN (+) and (-) circuits. One of the resistors is connected at the body control module (BCM) and the other is at the engine control module (ECM). When testing for a short between high speed GMLAN (+) and (-) a reading of 60 ohms is normal. If the high speed GMLAN serial data is open testing the resistance between high speed GMLAN (+) and (-) will read about 120 ohms.

The engine will not start when there is a total malfunction of the high speed GMLAN serial data circuits while the engine is not running. The following conditions may cause a total loss of high speed GMLAN data communication

1. A short between high speed GMLAN (+) and high speed GMLAN (-) circuits
2. Any of the high speed GMLAN serial data circuits shorted to ground or voltage
3. A module internal malfunction that causes a short to voltage or ground on the high speed GMLAN circuits
4. Any of the high speed GMLAN serial data circuits open

The numbers below refer to the step numbers on the diagnostic table.

1. 2: A partial malfunction in the high speed GMLAN serial data circuits uses a different procedure from a total malfunction of the high speed GMLAN data circuits. The following modules are connected to the high speed GMLAN serial data circuits: BCM Communication interface module (OnStar®) Distance sensing cruise control (DSCC) module Electronic brake control module (EBCM) Electronic suspension control (ESC) module Engine control module (ECM) Transmission control module (TCM)
2. 8: Data link connector terminals 6 and 14 provide the connection to the GMLAN serial data high circuit and the GMLAN serial data low circuit respectively.
3. 15: If only one of the high speed GMLAN circuits is open all communication on the high speed bus will be disrupted.
4. 19: The communication malfunction may have prevented diagnosis of the customer complaint.

Scan Tool Does Not Communicate with High Speed GMLAN Device

Retained Accessory Power (RAP) On After Timeout

Retained Accessory Power (RAP) On After Timeout

Retained Accessory Power (RAP) Inoperative

Retained Accessory Power (RAP) Inoperative

Control Module References

Control Module References

Data Link References

This table identifies which serial data link that a particular module uses for in-vehicle data transmission. Some modules may use more than one data link to communicate. Some modules may have multiple communication circuits passing through them without actively communicating on that data link. This table is used to assist in correcting a communication malfunction. The BCM emulates some devices that are on high speed GMLAN serial data circuit to the modules on class 2 serial data circuit. The BCM transmits multiple Node Alive messages using source IDs that correspond to each of those high speed GMLAN nodes. This is in addition to the BCM behaving itself as a real node. For the description and operation of these serial data communication circuits refer to Data Link Communications Description and Operation .

Data Link References

Removal Procedure

1. Turn OFF the ignition switch.
2. Remove the kick-up panel at the right front floor. Refer to «Front Floor Kick-Up Panel Replacement»(/cadillac/xlr/i-2003-2009/remont/exteriorinterior-trim/#interior-trim) .
3. Remove 3 retaining screws (1) which secure the body control module (BCM) (2) to the multi use bracket.
4. Disconnect the harness connectors from the BCM (2).
5. Remove the BCM (2) from the vehicle.

Installation Procedure

1. Turn OFF the ignition switch.
2. Connect the harness connectors to the BCM (2).
3. Position the BCM (2) to the multi use bracket.
4. Install 3 retaining screws (1) to the BCM (2). Tighten: Tighten the screws to 2 N.m (18 lb in).
5. Install the kick-up panel. Refer to «Front Floor Kick-Up Panel Replacement»(/cadillac/xlr/i-2003-2009/remont/exteriorinterior-trim/#interior-trim) .
6. If you are installing a new or replacement BCM, program the BCM to the current vehicle. Refer to «Control Module References»(/cadillac/xlr/i-2003-2009/remont/communication-devices/#computerintegrating-systems__control-module-references) .

1. Remove the screws from the data link connector.
2. Reposition the data link connector from the instrument panel.

1. Position the data link connector to the instrument panel.
2. Install the screws to the data link connector. Tighten: Tighten the data link connector screws to 2 N.m (18 lb in).

Introduction

A new body control module BCM must be programmed with the proper RPO configurations. The BCM stores the information regarding the vehicle options and if the BCM is not properly configured with the correct RPO codes, the BCM will not control all of the features properly. The Tech 2 software will automatically prompt you with the RPO's available for the vehicle. Ensure that the following conditions exist in order to prepare for BCM programming

1. The battery is fully charged.
2. The ignition mode switch is in the ON position.
3. All disconnected modules and devices are reconnected before programming.

A new BCM installed in the vehicle may set the DTC B1001 00 and DTC C0278 00. This is a normal condition and DTCs will clear after the BCM Setup and BPP Sensor Calibration procedures are performed.

1. BCM Setup
2. Program VIN
3. BPP Sensor Calibration

BCM Setup

Follow the instructions on the scan tool under Vehicle Control Systems>Module Replacement/Setup Procedures>BCM>BCM Setup to perform this procedure.

During this procedure, besides RPO configuration, the BCM relearns the restraints ID.

Program VIN

Follow the instructions on the scan tool under Vehicle Control Systems>Module Replacement/Setup Procedures>BCM>Program VIN to perform this procedure.

1. Turn the ignition OFF for 10 seconds.
2. Connect the scan tool to the data link connector.
3. Turn the ignition ON with the engine OFF.
4. Use the scan tool in order to retrieve history DTCs from all modules.
5. Clear all history DTCs.

BPP Sensor Calibration

Follow the instructions on the scan tool under Vehicle Control Systems>Module Replacement/Setup Procedures>BCM>BPP Sensor Calibration to perform this procedure.

The communication among modules is performed through the class 2 serial data circuit and high speed GMLAN serial data circuit. The modules that need real time communication are attached to the high speed GMLAN network. The body control module (BCM) is the gateway between the networks. The purpose of the gateway is to transfer information from one network to another. The gateway will interact with each network according to that network's transmission model. Refer to Body Control System Description and Operation for more information about the gateway.

Data Link Connector (DLC)

The data link connector (DLC) is a standardized 16-cavity connector. Connector design and location is dictated by an industry wide standard, and is required to provide the following

1. Scan tool power battery positive voltage at terminal 16
2. Scan tool power ground at terminal 4
3. Common signal ground at terminal 5
4. Class 2 signal at terminal 2
5. High speed GMLAN serial data bus (+) at terminal 6
6. High speed GMLAN serial data bus (-) at terminal 14

High Speed GMLAN Circuit Description

The data link connector (DLC) allows a scan tool to communicate with the high speed GMLAN serial data circuit. The serial data is transmitted on 2 twisted wires that allow speed up to 500 Kbps. The twisted pair is terminated with 2, 120 ohm, resistors; one is internal to the engine control module (ECM) and the other is internal to the body control module (BCM). The resistors are used to reduce noise on the high speed GMLAN bus during normal vehicle operation. The high speed GMLAN is a differential bus. The high speed GMLAN serial data bus (+) and high speed GMLAN serial data (-) are driven to opposite extremes from a rest or idle level. The idle level which is approximately 2.5 volts is considered a recessive transmitted data and is interpreted as a logic 1. Driving the lines to their extremes adds 1 volt to high speed GMLAN serial data bus (+) and subtracts 1 volt from high speed GMLAN serial data bus (-) wire. This dominant state is interpreted as a logic 0. GMLAN network management supports selective start up and is based on virtual networks. A virtual network is a collection of signals started in response to a vehicle event. The starting of a virtual network signifies that a particular aspect of the vehicle's functionality has been requested. A virtual network is supported by virtual devices which represents a collection of signals owned by a single physical device. So, any physical device can have one or more virtual devices. The signal supervision is the process of determining whether an expected signal is being received or not. Failsofting is the ability to substitute a signal with a default value or a default algorithm, in the absence of a valid signal. Some messages are also interpreted as a "heartbeat" of a virtual device. If such a signal is lost, the application will set a no communication code against the respective virtual device. This code is mapped on the Tech 2 screen as a code against the physical device. Note that a loss of serial data DTC does not normally represent a failure of the module that set it.

The interaction between high speed GMLAN and class 2 is assured by BCM, which is the gateway. Any message from the class 2 modules to the high speed GMLAN modules is translated by BCM without carrying the original transmitter ID. Therefore the GMLAN modules consider the BCM as being the originator of all class 2 messages that they receive. The GMLAN serial data communications circuit on this vehicle is in a linear topology. The following modules are connected to the link in order, from the DLC to the end of the linear configuration

1. The BCM
2. The communication interface module (OnStar®)
3. The electronic suspension control (ESC) module
4. The transmission control module (TCM)
5. The distance sensing cruise control module (DSCC)
6. The electronic brake control module (EBCM)
7. The ECM

Class 2 Circuit Description

The data link connector (DLC) allows a scan tool to communicate with the class 2 serial data circuit. Class 2 serial data is transmitted on a single wire at an average of 10.4 Kbps. The bus is active at 7 volts nominal and inactive at ground potential. When the ignition switch is in RUN, each module communicating on the class 2 serial data line sends a state of health (SOH) message every 2 seconds to ensure that the module is operating properly. When a module stops communicating on the class 2 serial data line, for example if the module loses power or ground, the SOH message it normally sends on the data line every 2 seconds disappears. Other modules on the class 2 serial data line, which expect to receive that SOH message, detect its absence; those modules in turn set an internal DTC associated with the loss of SOH of the non-communicating module. The DTC is unique to the module which is not communicating, for example, when the body control module (BCM) SOH message disappears, several modules set DTC U1064. Note that a loss of serial data DTC does not normally represent a failure of the module that set it.

The BCM emulates the GMLAN modules on the class 2, embedding the original transmitter ID in GMLAN messages to class 2. Therefore, the class 2 modules can set specific non-communications DTCs against GMLAN modules.

The class 2 serial data communications circuit on this vehicle is in a star configuration. The star has 2 splice packs, located as follows

1. The splice pack SP205 is located under the left side of the instrument panel, near the data link connector.
2. The splice pack SP208 is located under the right side of the instrument panel.

The following modules communicate on the class 2 serial data circuit

1. The splice pack SP205 attaches to: The driver door module (DDM) The driver door switch (DDS) The driver position module (DPM) The head up display (HUD) The instrument panel cluster (IPC) The inflatable restraint sensing and diagnostic module (SDM) The steering column lock control module (SCLCM)
2. The splice pack SP208 attaches to: The audio amplifier The BCM The communication interface module (OnStar®) The CD changer (CDX) The digital radio receiver (DRR) The folding top controller (FTC) The HVAC control module The passenger door module (PDM) The radio The remote control lock door receiver (RCDLR)

BCM Overview

The body control module (BCM) is an integrated module that combines functions and features from a normal control module and a body electrical center. There are four electrical interfaces that exist between the BCM and the rest of the vehicle. There are two connections from the BCM to both the body wiring harness and the instrument panel wiring harness. The BCM contains fuses and relays that are serviceable.

The main features of the BCM are

1. The BCM is the gateway between class 2 serial data circuit and high speed GMLAN serial data circuit.
2. The BCM controls multiple functions.
3. The BCM controls electrical power management.
4. The BCM is the power mode master.

Gateway

The BCM is the gateway between class 2 serial data circuit and high speed GMLAN serial data circuit. The purpose of the gateway is to transfer serial data messages from one sub net to another.

BCM Functions

The BCM performs multiple body control functions. The BCM can control devices directly connected to its outputs based on input information. The BCM evaluates this information and controls certain body control systems by commanding outputs on or off. The BCM inputs can be

1. Sensors and switches that are directly connected to the BCM
2. Class 2 serial data messages received from other vehicle systems connected to the class 2 serial data link
3. GMLAN serial data messages received from other vehicles systems connected to the high speed GMLAN serial data link

The BCM is also capable of controlling other vehicle systems that are not directly wired to the BCM. The BCM does this by sending specific messages on the class 2 serial data link or high speed GMLAN serial data link. The system capable of performing the required function will respond to the BCM messages.

Some of the other systems' functions that BCM controls or contributes to are

1. Audible warnings, refer to «Audible Warnings Description and Operation»(/cadillac/xlr/i-2003-2009/remont/gauges-instrument-panels/#instrument-panel-gages-and-console__audible-warnings-description-and-operation) in Instrument Panel, Gages and Console
2. Exterior lighting control, refer to «Exterior Lighting Systems Description and Operation»(/cadillac/xlr/i-2003-2009/remont/exterior-lights/#lighting-systems-introduction-2-of-2) in Lighting Systems
3. Interior lighting, refer to «Interior Lighting Systems Description and Operation»(/cadillac/xlr/i-2003-2009/remont/exterior-lights/#lighting-systems-introduction-2-of-2) in Lighting Systems
4. Automatic door locks, refer to «Power Door Locks Description and Operation»(/cadillac/xlr/i-2003-2009/remont/door-locks-anti-theft-systems/#door-system-mirror-system-window-system) in Doors
5. Keyless entry, refer to «Keyless Entry System Description and Operation»(/cadillac/xlr/i-2003-2009/remont/door-locks-anti-theft-systems/#keyless-entry-system) in Keyless Entry
6. Theft deterrent, refer to «Content Theft Deterrent (CTD) Description and Operation»(/cadillac/xlr/i-2003-2009/remont/door-locks-anti-theft-systems/#theft-deterrent-system__content-theft-deterrent-ctd-description-and) in Theft Deterrent
7. Wipers/washers, refer to «Wiper/Washer System Description and Operation»(/cadillac/xlr/i-2003-2009/remont/wiperwasher-systems/#wiper-system-washer-system) in Wipers/Washer Systems
8. Headlamp washer, refer to «Headlamp Washer System Description and Operation»(/cadillac/xlr/i-2003-2009/remont/wiperwasher-systems/#wiper-system-washer-system) in Wipers/Washer Systems
9. Cruise Control, refer to «Cruise Control Description and Operation (Adaptive Cruise)»(/cadillac/xlr/i-2003-2009/remont/cruise-control-systems/#cruise-control-system) or «Cruise Control Description and Operation (Conventional Cruise)»(/cadillac/xlr/i-2003-2009/remont/cruise-control-systems/#cruise-control-system__cruise-control-description-and-operation-conventional) in Cruise Control
10. Entertainment, refer to «Radio/Audio System Description and Operation»(/cadillac/xlr/i-2003-2009/remont/entertainment-systems/#entertainment-systems__radioaudio-system-description-and-operation) in Entertainment
11. Column lock, refer to «Steering Wheel and Column Description and Operation»(/cadillac/xlr/i-2003-2009/remont/steering-column-switches/#steering-wheel-steering-column) in Steering Wheel and Column

Electrical Load Management

The BCM controls electric power management following an idle boost and a load shed algorithm. The load shed control algorithm will deactivate electrical loads if the idle boost algorithm is unable to maintain system voltage. If idle boost is active for a certain amount of time and the system voltage is still below a set value, then load shed will command the heated seats, HVAC blower, and rear defog to deactivate periodically. The deactivations will be cycled such that the customer may not observe limited operation. The duty cycle will be controlled independently by each of heated seats, HVAC blower, and rear defog. If idle boost continues to be active, the engine RPM low, and the system voltage remains low, then load shed will command the heated seats, HVAC blower, and rear defog to deactivate completely. When this occurs, the DIC will display "Battery Saver Active". Once the idle boost becomes unnecessary or the engine RPM is above a set value, and the system voltage is above a set value, the load shed algorithm will command the heated seats, HVAC blower, and rear defog to resume normal operation.

Power Mode

The BCM is the power mode master (PMM). Refer to Power Mode Description and Operation for more information.

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 BCM. The BCM will monitor the mode switch only with battery voltage above 7 volts to prevent invalid input readings during low voltages encountered during vehicle cranking. If the mode switch input or the battery voltage input changes, a ratio metric calculation of mode switch input value is performed. The BCM discerns four thresholds

1. Inactive
2. Start active
3. Off active
4. Short detect

To determine the correct power mode the BCM uses

1. The mode switch data received from the ignition mode switch
2. The status of the engine run flag (ERF)

The following power mode states are transmitted on the class 2 network

1. Off
2. RAP
3. Accessory
4. Run
5. Crank

The following power mode states are transmitted on the GMLAN network

1. Off
2. Accessory
3. Run
4. Crank

The power mode message is a periodic with event message type and is transmitted by the PMM or BPMM at every 2 seconds on class 2 link and at every 250 ms on GMLAN link.

The Accessory power mode times out after 20 minutes and will transition to Off/Awake or RAP power mode.

Fail-safe Operation

The remote control door lock receiver (RCDLR) is the back up power mode master (BPMM). The both BCM and RCDLR receive signals from the ignition mode switch, representing the mode switch data, through 2 different circuits. Therefore if BPMM becomes enabled, it can determine and transmit all the system power modes per the lists above, except RAP. There is no degradation in system operation if the BPMM is the RCDLR. Since the operation of the vehicle systems depends on the power mode, there is a fail-safe plan in place if the power mode message is not received from the BCM or RCDLR. The fail-safe plan covers modules with discrete ignition signal inputs as well as those modules using exclusively serial data control of power mode. The engine control module (ECM) behaves differently.

Serial Data Messages

If no power mode message can be received, the modules remain in the last power mode received and check for the ERF message. If the ERF serial data is true, indicating that the engine is running, the modules fail-safe to "Run" power mode. 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" power mode.

Discrete Ignition Signals

Those modules that have Run/Crank discrete ignition signal input also remain in the state dictated by the last valid power mode message from the BCM or the RCDLR. They then check the state of their Run/Crank discrete ignition signal input to determine the current valid state. If the discrete ignition input is active, the modules will fail-safe to the "Run" power mode. If the discrete ignition input is inactive, the modules will fail-safe to "Off" power mode.

PCM and TCM Power Mode Backup Strategy

The PCM and TCM remain in the last known power mode state until it can determine its backup system power mode based on their discrete Accessory/Wake up and Run/Crank signal inputs.

PCM and TCM Power Mode Backup Strategy

Serial Data Control of Retained Accessory Power (RAP)

Retained accessory power (RAP) is a vehicle power mode that permits the operation of selected customer convenience items after the ignition switch is turned OFF. These selected items will remain in operation until a passenger compartment door is opened or until the RAP function timer reaches its shut-off limit.

The class 2 RAP power mode is mapped to GMLAN serial data circuit as Off power mode. Refer to Data Link Communications Description and Operation for more information on data link communications. The body control module (BCM) monitors the ignition mode signal from the ignition mode switch, battery condition and the doors status to determine whether RAP should be initiated. The modules that support the RAP power mode will operate the systems under their control as required by their RAP power mode strategy.

RAP will end when one of the following conditions is met

1. The BCM detects the opening of a passenger compartment door.
2. The RAP timer expires.
3. The battery capacity decreases below a prescribed limit.
4. Any other ignition switch state is chosen.

The functions supported in the RAP power mode are

1. The power windows
2. The IPC and DIC displays
3. The entertainment devices

See also:
• Power Distribution Schematics
• Master Electrical Component List
• Diagnostic System Check - Vehicle
• Circuit Testing
• Wiring Repairs
• Testing for Intermittent Conditions and Poor Connections
• Connector Repairs
• Ignition and Start Switch Replacement
• Diagnostic Trouble Code (DTC) List - Vehicle
• DTC U2153
• Checking Aftermarket Accessories
• Symptoms - Doors
• DTC Symptom Description
• Radio/Audio System Schematics
• Body Control Module Programming and Setup
• OnStar Schematics
• OnStar Reconfiguration (w/o SPS Programming)
• OnStar Reconfiguration (with TIS 2 Web and SPS Programming)
• Engine Cooling Schematics
• Cruise Control Schematics
• Cruise Control Module Programming and Setup
• Door Control Module Schematics
• Door Control Module Replacement
• Power Window Reinitialization
• Antilock Brake System Schematics
• Service Programming System (SPS)
• Suspension Controls Schematics
• Engine Controls Schematics
• Engine Controls Schematics
• Engine Control Module Replacement
• Engine Control Module Programming and Setup (4.6L)
• Exhaust System Schematics
• Folding Top Schematics
• Power Folding Top Learn
• Garage Door Opener Schematics
• Headlights/Daytime Running Lights (DRL) Schematics
• HVAC Schematics
• HVAC Control Module Programming and Setup
• SIR Schematics
• Passenger Presence System Programming and Setup
• Inflatable Restraint Sensing and Diagnostic Module Programming and Setup
• Driver Seat Schematics
• Memory Seat Control Module Programming and Setup
• Object Detection Schematics
• Radio Programming and Setup
• Keyless Entry Schematics
• Column/Ignition Lock Schematics
• Control Module Setup (SCLCM Setup)
• Automatic Transmission Controls Schematics
• Automatic Transmission Controls Schematics
• Transmission Control Module Programming and Setup
• Front Floor Kick-Up Panel Replacement
• Fastener Notice
• Audible Warnings Description and Operation
• Content Theft Deterrent (CTD) Description and Operation
• Wiper/Washer System Description and Operation
• Cruise Control Description and Operation (Conventional Cruise)
• Radio/Audio System Description and Operation
• DTC B0976, B0977, or B0978
• Control Module References
• Scan Tool Does Not Communicate with High Speed GMLAN Device
• Data Link References
• Retained Accessory Power (RAP) On After Timeout
• Retained Accessory Power (RAP) Inoperative