Circuit/System Description
The internal fault detection is handled inside the control module. No external circuits are involved.
Some control modules must be configured with serial numbers, vehicle options, or other information. If a control module was not properly configured after installation, that module may set DTC B1001.
Modules connected to the high and low 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. Each message contains the identification number of the transmitter module.
The wake up signal circuit is energized by the serial data gateway (SDG) module to activate the drive motor generator power inverter module (PIM) and the drive motor generator battery control module. If the wake up signal is not responded to by all three modules, this DTC sets in the SDG module.
Modules connected to the high and low 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. Each message contains the identification number of the transmitter module.
The wake up signal circuit is energized by the serial data gateway module (SDGM) to activate the accessory DC power control module (APM) immediately when the body control module (BCM) signals the SDGM that serial data is required.
When the ignition is turned ON, the microprocessor runs a diagnostic program to detect an internal fault when power up is commanded. If an internal malfunction is detected, the control module will store a DTC C0550 in its memory.
Modules connected to the 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 programmed information about what messages are needed to be exchanged on the serial data circuits. The messages are also supervised and some periodic messages are used by the receiver module as an availability indication of the transmitter module.
DTC U0020 will set when fewer modules are detected on the bus before the modules can learn the other modules IDs. If the communication bus is opened, or if the modules power supply is lost when the vehicle is in the OFF power mode, and then placed in the RUN power mode, U0020 will set in specific modules.
The serial data circuits are serial data buses are used to communicate information between the control modules. The serial data circuits also connect directly to the data link connector (DLC).
The PTLAN serial data circuits are serial data buses used to communicate information between the control modules. The PTLAN serial data circuits also connect directly to the data link connector (DLC) for programming purposes. If this serial data system is inoperative the modules will still communicate with the scan tool due to other serial data systems but not with each other. Communication with the scan tool for the modules on the PTLAN bus is through the serial data gateway module (SDGM) on the HSGMLAN serial data system.
The serial data circuit is the means by which the control modules in the vehicle communicate with each other. Once the scan tool is connected to the serial data circuit through the DLC, the scan tool can be used to monitor each module for diagnostic purposes and to check for diagnostic trouble codes (DTCs). When the ignition switch is in RUN, each control module communicating on the serial data circuit sends a state of health (SOH) message to ensure that the control module is operating properly. When a control module stops communicating on the serial data circuit, for example if the module loses power or ground, the SOH message it normally sends on the serial data circuit disappears. Other control modules on the serial data circuit, which expect to receive that SOH message, detect its absence; those control modules in turn sets a DTC associated with the loss of SOH of the non-communicating control module. The DTC is unique to the control module which is not communicating, for example, when the inflatable restraint sensing and diagnostic module (SDM) SOH message disappears, several modules set DTC U1088. Note: a loss of serial data communications DTC does not represent a failure of the module that set it.
The PTLAN serial data circuits are serial data buses used to communicate information between the control modules. The PTLAN serial data circuits also connect directly to the data link connector (DLC) for programming purposes. If this serial data system is inoperative the modules will still communicate with the scan tool due to other serial data systems but not with each other. Communication with the scan tool for the modules on the PTLAN bus is through the serial data gateway module (SDGM) on the HSGMLAN serial data system.
The driver door module (DDM) and the front passenger door module (FPDM) communicate with window regulator motors on the local interconnect network bus 1 and the local interconnect network bus 2 circuits respectively. When the driver power window switch is activated to a desired position, the DDM examines the request and checks for messages from other vehicle control modules prohibiting window movement. If no prohibitive messages have been received, the DDM will send a LIN serial data message to the driver door window motor to move the window to the desired position.
When the DDM receives a request to operate one of the right side passenger windows from the driver master control, a GMLAN serial data message is sent to the PDM. The PDM examines the request and checks for messages from other vehicle control modules prohibiting the window movement. If no prohibitive messages have been received, the PDM will send a LIN serial data message to the appropriate window motor to move the window as requested.
The DDM and PDM supply their respective rear power window switches with a 12-volt reference and signal circuit. The rear power window switches contain separate resistors for each switch position. When a rear power window switch is activated, the associated door control module interprets the signal and checks for messages from other vehicle control modules prohibiting the window movement. If no prohibitive messages have been received, the door control module sends a LIN serial data message to the appropriate power window motor commanding the requested window position.
The Driver Information Center (DIC) displays the compass based on serial data message from the BCM. The compass module communicates with the body control module (BCM) through a bi-directional data circuit (LIN).
The PTLAN serial data circuits are serial data buses used to communicate information between the control modules. The PTLAN serial data circuits also connect directly to the data link connector (DLC) for programming purposes. If this serial data system is inoperative the modules will still communicate with the scan tool due to other serial data systems but not with each other. Communication with the scan tool for the modules on the PTLAN bus is through the serial data gateway module (SDGM) on the HSGMLAN serial data system.
Modules connected to the high and low 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 some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module.
The serial data gateway (SDG) module translates serial data messages between the high speed GMLAN serial data bus, the low speed GMLAN serial data bus, and the high speed hybrid GMLAN serial data bus. Messages between the drive motor generator battery control module and the other hybrid system control modules must pass thru the SDG module. The wake up circuit sends a voltage from the SDG module to the drive motor generator battery control module to initiate certain module functions. DTC U1812 is set by the drive motor generator battery control module, but is stored in and reported by the hybrid powertrain control module (HPCM).
Modules connected to the high and low 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 some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module.
The serial data gateway (SDG) module translates serial data messages between the high speed GMLAN serial data bus, the low speed GMLAN serial data bus, and the high speed hybrid GMLAN serial data bus. Messages between the drive motor generator battery control module and the other hybrid system control modules must pass thru the SDG module. The wake up circuit sends a voltage from the SDG module to the drive motor generator battery control module to initiate certain module functions. DTC U1813 is set by the drive motor generator battery control module, but is stored in and reported by the hybrid powertrain control module (HPCM).
The accessory wake up serial data circuit is a voltage wake up signal from the body control module (BCM) to the engine control module (ECM) and the transmission control module (TCM). The signal is activated in 2 ways; any time the ignition switch is in the ACC or RUN position, or anytime the BCM determines that communication is needed from the powertrain. When the ignition switch is in the ACC or RUN position, the accessory voltage circuit input to the BCM is internally connected to the accessory wake up serial data circuit output, and voltage is supplied to the modules. The BCM also supplies voltage to the accessory wake up serial data circuit when it determines that communication is necessary with the powertrain and the ignition is not in the ACC or RUN position such as during remote start.
Modules connected to the high speed hybrid 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. Each message contains the identification number of the transmitter module.
The communication enable and the wake up circuits are energized by a specific module to activate another specific module when the ignition key is in ACC, ON or START. Only the modules using high speed GMLAN serial data are connected to the enable or wake up circuits. Refer to the appropriate schematics to determine which modules activate and are activated using the enable or wake up circuits.
The motor control module (MCM) 1, 2, and the hybrid powertrain control module (HPCM) are all internal to the drive motor power inverter module (PIM). The MCMs communicate only with the HPCM with the HPCM sending out DTC information to other modules regarding the MCMs. All circuits to the MCM are also internal to the PIM and is replaced as a single component.
Communication diagnostics for the serial data, including module power and ground as well as the wake up circuits for both MCMs, and the HPCM are all diagnosed from external sources only to the PIM connector because any circuit fault condition within the PIM will cause a complete replacement.
Modules connected to the high speed hybrid 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. Each message contains the identification number of the transmitter module.
The communication enable and the wake up circuits are energized by a specific module to activate another specific module when the ignition key is in ACC, ON or START. Only the modules using high speed GMLAN serial data are connected to the enable or wake up circuits. Refer to the appropriate schematics to determine which modules activate and are activated using the enable or wake up circuits.
The motor control module (MCM) 1, 2, and the hybrid powertrain control module (HPCM) are all internal to the drive motor power inverter module (PIM). The MCMs communicate only with the HPCM with the HPCM sending out DTC information to other modules regarding the MCMs. All circuits to the MCM are also internal to the PIM and is replaced as a single component.
Communication diagnostics for the serial data, including module power and ground as well as the wake up circuits for both MCMs, and the HPCM are all diagnosed from external sources only to the PIM connector because any circuit fault condition within the PIM will cause a complete replacement.
Modules connected to the PTLAN 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. Each message contains the identification number of the transmitter module.
Modules connected to the 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. Each message contains the identification number of the transmitter module.
DTC U1818 will set in the serial data gateway module (SDGM) when no communication is established with the ECM on the PTLAN serial data bus.
Modules connected to the PTLAN 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. Each message contains the identification number of the transmitter module.
Modules connected to the 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. Each message contains the identification number of the transmitter module.
DTC U1821 will set in the drive motor generator power inverter module when no communication is established with the accessory DC power control module on the PTLAN serial data bus.
Modules connected to the high and low 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. Each message contains the identification number of the transmitter module.
The serial data gateway module (SDGM) energizes the wake up signal to activate the accessory DC power control module (APM) when communication is needed. The SDGM monitors the signal circuit for faults.
Modules connected to the 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. Each message contains the identification number of the transmitter module.
Modules connected to the 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. Each message contains the identification number of the transmitter module.
Modules connected to the high and low 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 some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module.
The enable signal circuit is energized by the body control module (BCM) to activate multiple modules when the BCM determines that communication is required. Some modules may still become active due to their own ignition voltage source if the enable circuit is not functional. The serial data gateway (SDG) module translates serial data messages between the high speed GMLAN serial data bus, the low speed GMLAN serial data bus, and the high speed hybrid GMLAN serial data bus. Messages between the drive motor generator battery control module and the other hybrid system control modules must pass thru the SDG module. DTC U1862 is set by the drive motor generator battery control module, but is stored in and reported by the hybrid powertrain control module (HPCM).
Modules connected to the high and low 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. Each message contains the identification number of the transmitter module.
Modules connected to the 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. Each message contains the identification number of the transmitter module.
Modules connected to the 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. Each message contains the identification number of the transmitter module.
Modules connected to the high and low 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. Each message contains the identification number of the transmitter module.
The serial data communication enable and the accessory wake up serial data circuits are energized by a specific module to activate another specific module when the ignition key is in ACC, ON or START. Only the modules using high speed GMLAN serial data are connected to the enable or wake up circuits. Refer to the appropriate schematics to determine which modules activate and are activated using the enable or wake up circuits.
Modules connected to the high and low 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. Each message contains the identification number of the transmitter module.
The serial data communication enable and the accessory wake up serial data circuits are energized by a specific module to activate another specific module when the ignition key is in ACC, ON or START. Only the modules using high speed GMLAN serial data are connected to the enable or wake up circuits. Refer to the appropriate schematics to determine which modules activate and are activated using the enable or wake up circuits.
Modules connected to the high and low 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. Each message contains the identification number of the transmitter module.
The serial data communication enable and the accessory wake up serial data circuits are energized by a specific module to activate another specific module when the ignition key is in ACC, ON or START. Only the modules using high speed GMLAN serial data are connected to the enable or wake up circuits. Refer to the appropriate schematics to determine which modules activate and are activated using the enable or wake up circuits.
Modules connected to the high and low 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. Each message contains the identification number of the transmitter module.
The serial data communication enable and the accessory wake up serial data circuits are energized by a specific module to activate another specific module when the ignition key is in ACC, ON or START. Only the modules using high speed GMLAN serial data are connected to the enable or wake up circuits. Refer to the appropriate schematics to determine which modules activate and are activated using the enable or wake up circuits.
Modules connected to the 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. Each message contains the identification number of the transmitter module.
DTC U1885 will set in the hybrid powertrain control module (HPCM) when the drive motor generator battery control module (BECM) looses communication with the serial data gateway module (SDGM) on the HSGMLAN serial data bus. The BECM communicates only on the PTLAN serial data bus while the HPCM communicates on the PTLAN and the HSGMLAN serial data bus.
Modules connected to the high and low 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. Each message contains the identification number of the transmitter module.
The serial data communication enable and the accessory wake up serial data circuits are energized by a specific module to activate another specific module when the ignition key is in ACC, ON or START. Only the modules using high speed GMLAN serial data are connected to the enable or wake up circuits. Refer to the appropriate schematics to determine which modules activate and are activated using the enable or wake up circuits.
Modules connected to the high and low 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. Each message contains the identification number of the transmitter module.
The serial data gateway (SDG) module translates serial data messages between the high speed GMLAN serial data bus, the low speed GMLAN serial data bus, and the high speed hybrid GMLAN serial data bus. Messages between the drive motor generator battery control module and the other hybrid system control modules must pass thru the SDG module. Only the modules using high speed GMLAN serial data are connected to the enable or wake up circuits. Refer to the appropriate schematics to determine which modules activate and are activated using the enable or wake up circuits. DTC U1888 is set by the drive motor generator battery control module, but is stored in and reported by the hybrid powertrain control module
Modules connected to the high and low 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. Each message contains the identification number of the transmitter module.
The SDGM energizes the wake up signal to activate the accessory DC power control module (APM) and another wake up signal to activate the hybrid powertrain control module (HPCM) which is inside the drive motor power inverter module (PIM). The HPCM reports all DTC for the APM, therefore DTC U189A cannot be reported with the HPCM is inoperative.
The body control module (BCM) applies voltage to the high speed GMLAN serial data wake up circuit, when the ignition key is in ACC, ON or START to enable several modules for bus communication.
Depending on option content, modules that may receive the signal are as follows
- Electronic brake control module (EBCM)
- Electronic suspension control (ESC) module
- Distance sensing cruise control (DSCC) module
- Trailer brake control module
- Fuel pump flow control module
- Power take off module
Modules connected to the high and low 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. Each message contains the identification number of the transmitter module.
Wake up signal circuits are energized by the body control module (BCM) to activate the serial data gateway module (SDGM) and other modules, including the BECM, immediately when serial data is required. Additionally after receiving this signal the SDGM energizes another wake up signal to activate the drive motor generator battery control module (BECM) among others.
Modules connected to the LAN 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. Each message contains the identification number of the transmitter module.
2 wake up signal circuits (5986, 5985) are energized by the body control module (BCM) to activate multiple modules including the drive motor generator battery control module (BECM) when serial data is required. Wake up signal circuit (968) is energized by the serial data gateway module (SDGM) to activate the BECM immediately after the BCM energizes circuit 5986 and 5985. The BECM compares the status of both wake up circuits.
Modules connected to the CAN bus 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. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module.
The electronic brake control module (EBCM) activates the other modules connected to the CAN serial data circuits by applying voltage when the ignition key is in ACC, ON or START. The EBCM and the yaw and lateral accelerometer sensor are the only modules connected to the CAN bus serial data circuits.
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
- Scan tool B+ voltage at terminal 16
- Scan tool ground at terminal 4
- Common ground at terminal 5
The serial data is transmitted on two twisted wires that allow speeds up to 500 Kb/s. The twisted pair is terminated with two 120 ohms resistors, one is internal to the engine control module (ECM) and the other can be a separate resistor in a connector assembly or in another control module. The resistors are used as the load for the High Speed GMLAN buss 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 of approximately 2.5 V. Driving the lines to their extremes, adds one volt to the high speed GMLAN serial data bus (+) circuit and subtracts one volt from the high speed GMLAN serial data bus (-) circuit. If serial data is lost, control modules will set a no communication code against the non-communicating control module. Note that a loss of serial data DTC does not represent a failure of the module that set it.
Modules connected to the low speed GMLAN serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules when the ignition switch is in any position other than OFF. The low speed GMLAN serial data circuit uses JX 221, JX 339, and, if equipped, JX 223 as common connection points between some modules and the data link connector (DLC).
The serial data is transmitted on two twisted wires that allow speeds up to 500 Kb/s. The twisted pair is terminated with two 120 ohms resistors, one is internal to the engine control module (ECM) and the other can be a separate resistor in a connector assembly or in another control module. The resistors are used as the load for the Powertrain High Speed GMLAN buss during normal vehicle operation. The Powertrain High Speed GMLAN is a differential bus. The Powertrain High Speed GMLAN serial data bus (+) and Powertrain High Speed GMLAN serial data (-) are driven to opposite extremes from a rest or idle level of approximately 2.5 V. Driving the lines to their extremes, adds one volt to the Powertrain High Speed GMLAN serial data bus (+) circuit and subtracts one volt from the Powertrain High Speed GMLAN serial data bus (-) circuit. If serial data is lost, control modules will set a no communication code against the non-communicating control module. Note that a loss of serial data DTC does not represent a failure of the module that set it.
Body Control System Description and Operation
The body control system consists of the body control module (BCM), communications, and various input and outputs. Some inputs, outputs and messages require other modules to interact with the BCM. The BCM also has discrete input and output terminals to control the vehicle's body functions. The BCM is wired to the GMLAN high speed serial data buss and the GMLAN low speed serial data buss and acts as a gateway between them. If the BCM does not communicate the vehicle will not start due to the inability of the engine control module (ECM)/powertrain control module (PCM) and theft deterrent module (TDM) to communicate without the BCM providing the gateway function.