Data Communications System: Overview — Chevrolet Captiva I facelift (2011-2013)

Scheme 3

Scheme 3: High Speed GMLAN

Scheme 4

Scheme 4: Low Speed GMLAN and Linear Interconnect Network (LIN)

Scheme 5

Scheme 5: Chassis Expansion Bus

Scheme 6

Scheme 6: Serial Data Communications Enable and Accessory Wake Up

Scheme 7

Scheme 7: Power, Ground, and Data Communications

Scheme 8

Scheme 8: Subsystem References (1 of 3)

Scheme 9

Scheme 9: Subsystem References (2 of 3)

Scheme 10

Scheme 10: Subsystem References (3 of 3)

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.

The internal fault detection is handled inside the control module.

The electrically erasable programmable read-only memory (EEPROM) check sum error detection is handled inside the control module.

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

The internal fault detection is handled inside the control module. The symptom byte listed in the DTC Descriptor is for engineering reference only. No external circuit diagnosis is involved.

Some control modules must be configured with specific software, serial numbers, vehicle options, or other information. If a control module was not properly configured after installation that module may set DTC B101E. The symptom byte listed in the DTC Descriptor is for engineering reference only. No external circuit diagnosis is involved.

The telematic vehicle localization and immobilization control module communicates with the scan tool via the keyword 2000 serial data circuit. The keyword 2000 system is for diagnostics of the telematic vehicle localization and immobilization control module only. There is no communication between any other control modules on the keyword 2000 serial data system.

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.

The internal fault detection is handled inside the control module. The symptom byte listed in the DTC Descriptor is for engineering reference only. No external circuit diagnosis is involved.

Some control modules must be configured with specific software, serial numbers, vehicle options, or other information. If a control module was not properly configured after installation that module may set DTC C056E. The symptom byte listed in the DTC Descriptor is for engineering reference only. No external circuit diagnosis is involved.

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 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 data link connector (DLC), the scan tool can be used to monitor each control 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 control 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 set 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 and one or more control modules may set the same exact code. A loss of serial data communications DTC does not represent a failure of the control modules that contain the stored code.

Modules connected to the CAN bus serial data circuits are high speed serial data modules that 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, Yaw Rate Sensor, and the Steering Angle Sensor are the only modules connected to the CAN bus serial data circuits. For more information on CAN bus serial data refer to Data Link Communications Description and Operation.

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 the Local Interconnect Network (LIN) bus circuit.

The powertrain wake-up communication 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 powertrain wake-up communication circuit output, and voltage is supplied to the control modules. The BCM also supplies voltage to the powertrain wake-up communication 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.

The body control module (BCM) applies voltage to the data communication enable 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

Transfer case control module (TCCM)
Electronic brake control module (EBCM)

Control 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 control modules. The control 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 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 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 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 control 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 200 and JX 209 as common connection points between some modules and the data link connector (DLC).

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 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/powertrain control module (ECM/PCM) and vehicle theft deterrent (VTD) control module to communicate without the BCM providing the gateway function.

Controller Area Network (CAN) Description

The EBCM communicates with the yaw rate sensor and the steering wheel angle sensor exclusively, when equipped. This serial data system does not communicate with the scan tool however; there are loss of communication DTCs for this system which set in the EBCM. The yaw rate sensor and the steering wheel angle sensors are in effect modules, exchanging essential information with the EBCM. For more information about these sensors refer to ABS Description and Operation. The CAN system functions in a manner similar to high speed GMLAN. A key difference is circuit voltage. In this CAN application the EBCM places 3 volts on the CAN bus high serial data circuit and 2 volts on the CAN bus low serial data circuit. The Yaw rate and steering angle sensors, when either are present, drive both circuits to a 2.5 voltage level. Communications occurs when the circuits are then switched to 3 volts and 2 volts respectively. Expected values would be 3 volts and 2 volts when using a digital multimeter to test these circuits with the sensors disconnected and approximately 2.5 volts on both with either sensor connected.

Data Communications System: Overview Chevrolet Captiva I facelift