Data Link Communication System Cadillac CTS I

Fastener Tightening Specifications

Fastener Tightening Specifications

Data Link Communications Schematic Icons

Data Link Communications 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 Zones. 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)

Scheme 1

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Scheme 4

Scheme 5

Scheme 6

Scheme 7

Data Link Communications Connector End Views

Data Link Connector (DLC) Connector Part Information 12110250 16-Way F Metri-Pack 150 Series (BK) Pin Wire Color Circuit Number Function 1 - - Not Used 2 PU 1807 Class 2 Serial Data 3 - - Not Used 4 BK 350 Ground 5 BK/WH 351 Ground 6 WH 2500 High Speed GMLAN Serial Data Bus+ (LY7 w/M82) 7 WH/BK 5043 Keyword 2000 Serial Data (LA3/LY9 w/M82) 8-13 - - Not Used 14 L-GN 2501 High Speed GMLAN Serial Data Bus- (LY7 w/M82) 15 - - Not Used 16 RD/WH 1140 Battery Positive Voltage

Diagnostic Starting Point - Data Link Communications

Begin the diagnosis of the data link communications by performing the Diagnostic System Check for the system in which the customer concern is apparent. The Diagnostic System Check will direct you to the correct procedure within the Data Link Communications section when a communication malfunction is present.

Diagnostic Trouble Code (DTC) List

Diagnostic Trouble Code (DTC) List

Circuit Description

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.

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.

Conditions for Setting the DTC

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.

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.

Diagnostic Aids

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/cts/i-2002-2007/remont/communication-devices/#data-link-communication-system__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 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/cts/i-2002-2007/remont/communication-devices/#data-link-communication-system__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. GMLAN serial data messages contain the identification number of the transmitter module. When a message that indicates the availability of the transmitter module is not received, the receiver module sets a DTC 0xxx where xx is equal to the 3-digit identification number of the transmitter module.

The control module ID number list below provides a method for determining which module is not communicating. A module with a GMLAN serial data circuits 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 can not communicate.

GMLAN ID

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.

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.

Action Taken When the DTC Sets

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.

Test Description

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

1. 2: This DTC sets when a communication fault exists between the engine control module (ECM) and the TCM. Inspect for DTCs U0001 or U0101. If any of these DTCs are present, diagnose them first.
2. 3: If a module is not awake, the modules expecting to receive data cannot detect the presence of the transmitting module.
3. 6: The TCM needs time to reset memory.

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 seconds of beginning serial data communication, DTC U1000 or U1255 DTC 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 class 2 serial data communications circuit on this vehicle is in a hybrid ring and star configuration. Each module on the ring has 2 serial data circuits connected to it, except the following modules have only 1 serial data circuit connected them

1. The audio amplifier
2. The drive door module (DDM)
3. The driver door switch assembly (DDSA)
4. The front passenger door module (FPDM)
5. The left rear door module (LRDM)
6. The memory seat module (MSM)
7. The radio antenna module
8. The rear integration module (RIM)
9. The right rear door module (RRDM)
10. The theft deterrent control module
11. The TV antenna module
12. The vehicle communication interface module (VCIM)

The star has 4 splice packs

1. SP200 located in the left side of the instrument panel, near the steering column, taped to the instrument panel harness.
2. SP201 located in the center of the instrument panel, near the radio.
3. SP300 located in the left side middle of the passenger compartment, taped to the body harness, near the carpet seam.
4. SP303 located in the right rear of the passenger compartment, taped to the body harness, approximately 24 cm (9.5 in) from the fuse block - right rear.

Refer to Data Link Connector (DLC) Schematics .

The following modules and splice packs are connected to the ring portion of the class 2 serial data circuit

1. The dash integration module (DIM)
2. The electronic brake control module (EBCM)
3. The electronic control module (ECM)
4. The inflatable restraint sensing and diagnostic module (SDM)
5. The instrument panel cluster (IPC)
6. The HVAC control module
7. The radio
8. The rear integration module (RIM)
9. The vehicle communication interface module (VCIM)
10. SP200
11. SP201
12. SP300
13. SP303

The following modules are connected to the star portion of the class 2 serial data circuit

1. SP300 The audio amplifier The driver door module (DDM) The driver door switch assembly (DDSA) The memory seat module (MSM) The left rear door module (LRDM)
2. SP303 The antenna module The front passenger door module (FPDM) The rear integration module (RIM) The right rear door module (RRDM) The theft deterrent control module The vehicle communication interface module (VCIM)

Refer to Data Link Connector (DLC) Schematics and Data Link Communications Description and Operation in order to familiarize yourself with the architecture of the class 2 serial data circuit

Conditions for Running the DTC

1. The following DTCs do not have a current status: B1327 B1328 U1300 U1301 U1305
2. 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 seconds after establishing class 2 serial data communication.

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.

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. 1: A DTC U1001 - U1254 Lost Communications with XXX with a history status may indicate the cause of U1000 or U1255.
2. 2: 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. 6: 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. 9: 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. 14: 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 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 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 can not communicate.

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.

1. The following DTCs do not have a current status: B1327 B1328 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.

When multiple Loss of Communication DTCs are set concurrently, the cause is likely to be 2 opens in the ring portion of the class 2 serial data circuit. Use the Control Module ID Number list in order to determine which modules are not communicating. Use the class 2 serial data circuit schematic in order to determine the location of the opens.

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

1. 6: The module which was not communicating on the class 2 serial data circuit may have set Loss of Communication DTCs for those modules that it was monitoring.

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.

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.

1. These DTCs cannot be retrieved with a current status. Diagnosis of current DTCs is accomplished via the symptom, Scan Tool Does Not Communicate with a Class 2 Device. Refer to «Scan Tool Does Not Communicate with Class 2 Device»(/cadillac/cts/i-2002-2007/remont/communication-devices/#data-link-communication-system) .
2. An intermittent condition is likely to be caused by a short on the class 2 serial data circuit. Use the Scan Tool Does Not Communicate with a Class 2 Device procedure in order to isolate an intermittent condition. Refer to «Scan Tool Does Not Communicate with Class 2 Device»(/cadillac/cts/i-2002-2007/remont/communication-devices/#data-link-communication-system) .

The controller area network (CAN) serial data line is a high speed serial data bus used to communicate information between the engine control module (ECM) and the transmission control module (TCM). Typical data-transmission speeds must be high enough to ensure that the required real-time response is maintained.

The CAN serial data line does not communicate with the scan tool via the DLC. CAN serial data information is interpreted by the ECM and transmitted to the serial data line by the ECM.

The CAN circuits are monitored continuously by the modules on the circuit. The only requirement is that the modules are in a RUN power mode.

The module setting the DTC has attempted to establish communications on the CAN circuits for more than 5 seconds.

The module uses a default value for the missing parameter.

Conditions for Clearing the MIL/DTC

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

DTC U2100

The Controller Area Network (CAN) serial data line is a high speed serial data bus used to communicate information between the engine control module (ECM) and the transmission control module (TCM). Typical data-transmission speeds must be high enough to ensure that the required real-time response is maintained.

The CAN serial data line does not communicate with the scan tool via the DLC. CAN serial data information is interpreted by the ECM and transmitted to the serial data line by the ECM.

The diagnostic for this DTC is run when the ignition is cycled from OFF to RUN.

The DTC is generated when the ECM is not calibrated to the vehicle.

1. The control module stores the DTC information into memory when the diagnostic runs and fails.
2. The malfunction indicator lamp (MIL) will not illuminate.
3. The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
4. The driver information center, if equipped, may display a message.

1. A current DTC Last Test Failed clears when the diagnostic runs and passes.
2. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
3. Clear the DTC with a scan tool.

The most likely occurrence of this DTC being set is due to incorrect calibration files downloaded to the ECM, or an ECM installed in the vehicle without the reprogramming procedure having been performed.

DTC U2102

The controller area network (CAN) serial data line is a high speed serial data bus used to communicate information between the engine control module (ECM) and the transmission control module (TCM). Typical data-transmission speeds must be high enough to ensure that the required real-time response is maintained.

The CAN serial data line does not communicate with the scan tool via the DLC. CAN serial data information is interpreted by the ECM and transmitted to the serial data line by the ECM.

The CAN circuits are monitored continuously by the modules on the circuit. The only requirement is that the modules are in a RUN power mode.

The module setting the DTC has attempted to establish communications on the CAN circuits for more than 5 seconds.

The DTC is set as both current and history, the modules on the CAN network each take separate actions as listed

1. Engine Control Module (ECM): Turn ON the MIL during the third consecutive drive cycle with the error detected. Record the operating conditions at the time of turning on the MIL and store the data as freeze frame information.
2. Transmission Control Module (TCM): SERVICE TRANSMISSION message is displayed when the first error is detected. Transmission operates in the default mode.

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

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

1. 2: This DTC sets when a communication fault exists between the ECM and the TCM. Inspect for DTCs U2100, U2102 or U2106. If any of these DTCs are present, diagnose them first.
2. 3: If a module is not awake, the modules expecting to receive data cannot detect the presence of the transmitting module.
3. 7: The TCM needs time to reset memory.

DTC U2106

Symptoms - Data Link Communications

1. Perform the applicable diagnostic system check 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 line.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to «Data Link Communications Description and Operation»(/cadillac/cts/i-2002-2007/remont/communication-devices/#data-link-communication-system) .

Visual/Physical Inspection

1. Inspect for aftermarket devices which could affect the operation of the vehicle systems. Refer to «Checking Aftermarket Accessories»(/cadillac/cts/i-2002-2007/remont/body-electrical/#wiring-systems-diagnostic-information-and-procedures__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/cts/i-2002-2007/remont/communication-devices/#data-link-communication-system)
2. «Scan Tool Does Not Communicate with Class 2 Device»(/cadillac/cts/i-2002-2007/remont/communication-devices/#data-link-communication-system)
3. «Scan Tool Does Not Communicate with Keyword Data Line»(/cadillac/cts/i-2002-2007/remont/communication-devices/#data-link-communication-system)
4. «Scan Tool Does Not Communicate with High Speed GMLAN Device»(/cadillac/cts/i-2002-2007/remont/communication-devices/#data-link-communication-system__scan-tool-does-not-communicate-with)

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 engine will not start when there is a total loss of class 2 serial data communication while the ignition is OFF. The following conditions will cause a total loss of class 2 serial data communication

1. A class 2 serial data circuit shorted to ground.
2. A class 2 serial data circuit shorted to voltage.
3. An internal condition within a module or connector on the class 2 serial data circuit, that causes a short to voltage or ground to the class 2 serial data circuit.

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

1. 2: A partial loss of communication in the class 2 serial data circuit uses a different procedure than a total loss of communication of the class 2 serial data circuit.
2. 4: The following DTCs may be retrieved with a history status. These DTCs are not the cause of the present condition. U1300 U1301 U1305
3. 6: A State of Health DTC with a history status may be present along with a U1000 or U1255 with a current status. This indicates that the malfunction occurred when the ignition was on.
4. 10: Normal class 2 serial data communication cannot take place until the power mode master (PMM) module sends the appropriate power mode message. If the PMM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate.
5. 12: Disconnecting the splice packs one at a time and attempting to communicate with any module still connected to the class 2 serial data circuit, will determine whether or not the concern is in the star portion of the class 2 serial data circuit.
6. 13: Connecting the class 2 serial data circuits to the suspect splice pack one at a time while attempting to communicate with any module still connected to the class 2 serial data circuit, will determine which circuit or module on the star is causing the concern.
7. 14: Splitting the class 2 serial data circuit will help isolate the location of the malfunction. If communication can be established, the concern is located in the wiring or one of the modules that is no longer connected to the DLC. If communication cannot be established, the concern is located in the wiring or one of the modules that is still connected to the DLC.
8. 22: If there are no current DTCs that begin with the letter "U", the communication concern has been repaired.
9. 23: The communication concern may have prevented diagnosis of the customer complaint.

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 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

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 communicate on the high speed GMLAN serial data circuits: Engine control module (ECM) Transmission control module (TCM)
2. 6: 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.

Scan Tool Does Not Communicate with High Speed GMLAN Device

The Keyword protocol utilizes a single wire bi-directional data line between the modules and the scan tool. The message structure is a request and response arrangement. Keyword serial data is used for scan tool diagnostics only. The modules do not exchange data on this circuit.

The following modules are connected to the Keyword serial data circuit

1. Engine Control Module (ECM)
2. Transmission Control Module (TCM) w/M82
3. Headlamp Assembly-LF w/export
4. Headlamp Assembly-RF w/export

Scan Tool Does Not Communicate with Keyword Data Line

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. 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. Lower the I/P closeout panel. Refer to «Closeout/Insulator Panel Replacement - Left»(/cadillac/cts/i-2002-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) .
2. Remove the screws securing the data link connector to the I/P carrier.

Installation Procedure

1. Install the screws securing the data link connector to the I/P carrier. Tighten: Tighten the screws to 2 N.m (18 lb in).
2. Install the I/P closeout panel. Refer to «Closeout/Insulator Panel Replacement - Left»(/cadillac/cts/i-2002-2007/remont/gauges-instrument-panels/#instrument-panel-system-displays-gauges-and-console) .

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 serial data at terminal 2.
5. Keyword serial data at terminal 7.
6. GMLAN (+) serial data at terminal 6 w/LY7.
7. GMLAN (-) serial data at terminal 14 w/LY7.

The serial data circuits are the means by which the control modules on the vehicle communicate with each other and the scan tool. There are 3 different types of protocols on this vehicle.

1. The class 2 serial data
2. The control area network (CAN) serial data w/M82
3. The keyword serial data

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. Refer to Body Control System Description and Operation in Body Control System for operation of the PMM.

Class 2 Serial Data

The data link connector (DLC) allows a scan tool to communicate with the class 2 serial data line. This serial data line is the means by which the microprocessor-controlled modules in the vehicle communicate with each other. Once the scan tool is connected to the class 2 serial data line through the DLC, the scan tool can be used to monitor each module for diagnostic purposes and to check for diagnostic trouble codes (DTCs). Class 2 serial data is transmitted on a single wire at an average of 10.4 kbps. This value is an average, class 2 uses a variable pulse width modulation to carry data and depending on the message it may operate faster or slower. The bus will float at a nominal 7.0 volts during normal operation. Each module can pull this lower during the transmission. The bus is not at battery positive voltage or ground potential during normal operation. 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 inflatable restraint sensing and diagnostic module (SDM) SOH message disappears, several modules set DTC U1088. Note that a loss of serial data DTC does not normally represent a failure of the module that set it.

Class 2 Serial Data Circuit Left Hand Drive (LHD)

The class 2 serial data circuit on this vehicle consists of a hybrid ring and star configuration. Each module on the ring has 2 class 2 serial data circuits connected to it. If there is 1 open on the ring serial data communication will still take place. If there is more than 1 open on the ring, the modules not connected to the class 2 serial data circuit will not communicate. If there is 1 open on the star, the module not connected to the class 2 serial data circuit will not communicate. The following modules and splice packs are connected to the class 2 serial data circuit in a ring fashion

1. SP201
2. The instrument panel cluster (IPC)
3. SP200
4. The electronic brake control module (EBCM)
5. The electronic control module (ECM)
6. The HVAC control module
7. The radio
8. The dash integration module (DIM)
9. SP303
10. The inflatable restraint sensing and diagnostic module (SDM)
11. SP300

The star has the following 4 splice packs

1. SP201 located in the center of the instrument panel, near the radio.
2. SP200 located in the left side of the instrument panel, near the steering column, taped to the instrument panel harness.
3. SP303 located in the right rear of the passenger compartment, taped to the body harness, approximately 24 cm (9.5 in) from the fuse block - right rear.
4. SP300 located in the left side middle of the passenger compartment, taped to the body harness, near the carpet seam.

The following devices are connected to the class 2 serial data circuit in star fashion via splice packs

1. SP201 - The DLC
2. SP303 The right rear door module (RRDM) The radio antenna module The TV antenna module The vehicle communication interface module (VCIM) The rear integration module (RIM) The front passenger door module (FPDM)
3. SP300 The audio amplifier The left rear door module (LRDM) The driver door switch assembly (DDSA) The driver door module (DDM) The memory seat module (MSM) w/A45
4. SP200 - The theft deterrent control module

Refer to Data Link Connector (DLC) Schematics and the following illustration in order to familiarize yourself with the architecture of the class 2 serial data circuit

Scheme 8

Class 2 Serial Data Circuit Right Hand Drive (RHD)

The class 2 serial data circuit on this vehicle consists of a hybrid ring and star configuration. Each module on the ring has 2 class 2 serial data circuits connected to it. If there is 1 open on the ring serial data communication will still take place. If there is more than 1 open on the ring, the modules not connected to the class 2 serial data circuit will not communicate. If there is 1 open on the star, the module not connected to the class 2 serial data circuit will not communicate. The following modules and splice packs are connected to the class 2 serial data circuit in a ring fashion

1. SP201
2. SP303
3. The inflatable restraint sensing and diagnostic module (SDM)
4. SP300
5. The dash integration module (DIM)
6. The radio
7. The HVAC control module
8. The electronic control module (ECM)
9. The electronic brake control module (EBCM)
10. SP200
11. The instrument panel cluster (IPC)

The star has the following 4 splice packs

1. SP201 located in the right side of the instrument panel, near the steering column, taped to the instrument panel harness.
2. SP303 located in the right rear of the passenger compartment, taped to the body harness, approximately 24 cm (9.5 in) from the fuse block - right rear.
3. SP300 located in the left side middle of the passenger compartment, taped to the body harness, near the carpet seam.
4. SP200 located in the center of the instrument panel, near the radio.

The following devices are connected to the class 2 serial data circuit in star fashion via splice packs

1. SP201 - The DLC
2. SP303 The right rear door module (RRDM) The radio antenna module The TV antenna module The vehicle communication interface module (VCIM) The rear integration module (RIM) The memory seat module (MSM) w/A45 The driver door module (DDM) The driver door switch assembly (DDSA)
3. SP300 The audio amplifier The left rear door module (LRDM) The front passenger door module (FPDM)
4. SP200 - The theft deterrent control module

Refer to Data Link Connector (DLC) Schematics and the following illustration in order to familiarize yourself with the architecture of the class 2 serial data circuit

Scheme 9

Controller Area Network (CAN) Serial Data Line w/M82

The Controller Area Network (CAN) serial data line does not communicate with the scan tool via the data link connector (DLC). CAN serial data information is interpreted by the engine control module (ECM) and transmitted to the class 2 serial data line by the ECM. The following modules communicate on the CAN serial data line

1. The ECM w/LA3/LY9
2. The TCM w/LA3/LY9

The CAN serial data line is high speed serial data bus used to communicate information between the engine control module (ECM) and the transmission control module (TCM). Typical data-transmission speeds must be high enough to ensure that the required real-time response is maintained.

The addressing scheme employed with CAN assigns a label to every message, with each message receiving a unique identifier. The identifier classifies the content of the message. Each module processes only those messages whose identifiers are stored in the module's acceptance list. This is CAN's form of message filtering.

The identifier labels both the data content and the priority of the message being sent. Each module can begin transmitting its most important data as soon as the bus is unoccupied. When more than one module starts to transmit simultaneously, the message with the highest priority is assigned first access. A module responds to failure to gain access by automatically switching to receive mode, the module then repeats the transmission attempt as soon as the bus is free again.

Keyword Serial Data Line

The keyword protocols utilize a single wire bi-directional data line between the modules and the scan tool. The message structure is a request and response arrangement. The keyword serial data line is used for scan tool diagnostics only. The modules do not exchange data on this circuit.

The modules on the keyword serial data line can include the following

1. Engine control module (ECM)
2. Transmission control module (TCM)
3. Headlamp assembly-LF w/TR7
4. Headlamp assembly-RF w/TR7

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 two twisted wires that allow speed up to 500 Kbps. The twisted pair is terminated with two 120 ohm resistors, one is internal to the engine control module (ECM) and the other is internal to the transmission control module (TCM). 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.

The modules on the GMLAN serial data line are

1. The ECM w/LY7
2. The TCM w/LY7

See also:
• Master Electrical Component List
• Inline Harness Connector End Views
• Control Module References
• Circuit Testing
• Wiring Repairs
• Testing for Intermittent Conditions and Poor Connections
• Connector Repairs
• Diagnostic System Check - Engine Controls
• Service Programming System (SPS)
• Engine Control Module (ECM) Replacement
• Diagnostic Trouble Code (DTC) List
• Checking Aftermarket Accessories
• Body Control System Description and Operation
• Closeout/Insulator Panel Replacement - Left
• DTC U0001
• Scan Tool Does Not Communicate with High Speed GMLAN Device
• Diagnostic Trouble Code (DTC) List
• Data Link Communications Connector End Views