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Data Communication System: Diagnosis Saturn Aura I

Communication Devices ~6849 words

DIAGNOSTIC CODE INDEX

DTCDescription
DTC B1000B1000 00: Engine Control Unit Performance - No Additional Information B1000 31: Engine Control Unit Performance - General Checksum Error B1000 57: Engine Control Unit Performance - Expected Reaction After Event Did Not Occur
DTC B1001B1001 00: Option Configuration Error B1001 45: Option Configuration Error Variant Not Programmed B1001 46: Option Configuration Error B1001 4B: Option Configuration Error Calibration Not Learned
DTC B1004B1004: Keep Alive Memory (KAM) Reset
DTC B1009B1009: EEPROM Checksum Mismatch
DTC C0550C0550 00: EEPROM Checksum Mismatch C0550 39: EEPROM Checksum Mismatch
DTC U0001U0001 00: High Speed CAN Communication Bus
DTC U0073U0073: High Speed Communication Bus
DTC U0100-U0299U0100 00: Lost Communication With ECM/PCM U0100 75: Lost Communication With ECM/PCM U0100 7F: Lost Communication With ECM/PCM U0101 00: Lost Communication With TCM U0102 00: Lost Communication With Transfer Case Control Module U0104 00: Lost Communication With Cruise Control Module U0104 7F: Lost Communication With Cruise Control Module U0106 00: Lost Communication With Glow Plug Control Module U0109 00: Lost Communication With Fuel Pump Control Module U0117 00: Lost Communication With Electrical PTO Control Module U0121 00: Lost Communication With Anti-Lock Brake System (ABS) Control Module U0122 00: Lost Communication With Vehicle Dynamics Control Module U0131 00: Lost Communication With Power Steering Control Module U0132 00: Lost Communication With Ride Level Control Module U0134 00: Lost Communication With Power Steering Control Module - Rear U0136 00: Lost Communication With Differential Control Module - Rear U0140 00: Lost Communication With Body Control Module U0141 00: Lost Communication With Body Control Module A U0151 00: Lost Communication With Restraints Control Module U0151 71: Lost Communication With Restraints Control Module Invalid Serial Data Received U0151 7F: Lost Communication With Restraints Control Module Erratic U0155 00: Lost Communication With Instrument Panel Cluster (IPC) Control Module U0156 00: Lost Communication With Information Center A (DIC) U0158 00: Lost Communication With Head Up Display U0159 00: Lost Communication With Parking Assist Control Module U0160 00: Lost Communication With Audible Alert Control Module U0164 00: Lost Communication With HVAC Control Module U0165 00: Lost Communication With HVAC Control Module - Rear U0168 00: Lost Communication With Vehicle Security Control Module U0170 00: Lost Communication With Restraints System Sensor A (PPS) U0172 00: Lost Communication With Rollover Sensor U0184 00: Lost Communication With Radio U0186 00: Lost Communication With Audio Amplifier U0291 00: Lost Communication With Television U0194 00: Lost Communication With Digital Radio Receiver (DRR) U0198 00: Lost Communication With Telematic Control Module U0199 00: Lost Communication With Door Control Module A (DDM) U0200 00: Lost Communication With Door Control Module B (PDM) U0208 00: Lost Communication With Seat Control Module A (DSM/MSM) U0209 00: Lost Communication With Seat Control Module B (HVSM) U0210 00: Lost Communication With Seat Control Module C (RHVSM) U0214 00: Lost Communication With Remote Function Actuation U0230 00: Lost Communication With Rear Gate Module U0232 00: Lost Communications With Side Object Detection (SOD) Module - Left U0233 00: Lost Communications With Side Object Detection (SOD) Module - Right U0236 00: Lost Communications With Column Locking Module (CLM) U0241 00: Lost Communication With Headlamp Control Module A U0249 00: Lost Communication With Entertainment Control Module - Rear B
DTC U1866-U1899U1866: Battery Energy Control Module Lost Communication With Body Control Module U1886: Battery Energy Control Module Lost Communication With Engine Control Module/Powertrain Control Module U1897: Starter/Generator Control Module Lost Communication With Battery Energy Control Module U1899: Starter/Generator Control Module Lost Communication With Engine Control Module/Powertrain Control Module
DTC U2100U2100: Controller Area Network (CAN) Bus Communication
DTC U2103U2103 00: Fewer Controllers On Than Programmed
DTC U2105-U2199U2105: Lost Communication With Engine Control System U2106: Lost Communication With Transmission Control System U2107: Lost Communication With Body Control System U2108: Lost Communication With ABS/TCS Control System U2109: Lost Communication With Powertrain Control System U2110: Lost Communication With Chassis Multiple Control System U2111: Lost Communication With Steering Control System U2112: Lost Communication With Electronic Suspension Control (ESC) U2113: Lost Communication With Sensing and Diagnostic Module (SDM) U2114: Lost Communication With PPS or CPS U2115: Lost Communication With (Restraints Control System) U2116: Lost Communication With Instrument Panel Cluster (IPC) U2117: Lost Communication With Driver Information Center (DIC) U2118: Lost Communication With Head Up Display (HUD) U2119: Lost Communication With Daytime Running Lamps (DRL) System U2120: Lost Communication With Automatic Headlamp Leveling Device (AHLD) U2121: Lost Communication With Radio Display U2122: Lost Communication With Radio U2123: Lost Communication With Compact Disc Changer (CDX) U2124: Lost Communication With Audio Amplifier U2125: Lost Communication With Telematic Unit U2126: Lost Communication With (Mobile Communications Control System) U2127: Lost Communication With Front HVAC U2128: Lost Communication With Rear HVAC U2129: Lost Communication With Remote Function Actuator (RFA) U2130: Lost Communication With Driver Door Module (DDM) U2131: Lost Communication With Driver Seat Module (DSM) U2132: Lost Communication With Passenger Door Module (PDM) U2133: Lost Communication With Passenger Seat Module (PSM) U2134: Lost Communication With Rear Door Module (RDM) U2135: Lost Communication With Rear Integration Module (RIM) U2136: Lost Communication With Memory Mirror Module (MMM) U2137: Lost Communication With Vehicle Theft Deterrent (VTD) U2138: Lost Communication With Column Locking Module (CLM) U2139: Lost Communication With Column Integration Module (CIM) U2140: Lost Communication With Underhood Electrical Center (UEC) U2141: Lost Communication With Rear Electrical Center (REC) U2142: Lost Communication With Yaw Rate Sensor (YRS) U2143: Lost Communication With Steering Angle Sensor (SAS) U2144: Lost Communication With Distance Sensing Cruise Control Module U2145: Lost Communication With Parking Assistance System (PAS) U2146: Lost Communication With Shift Lever Module (SLM) U2147: Lost Communication With Auxiliary Heater System (AHS) U2148: Lost Communication With Sun Roof Module (SRM) U2149: Lost Communication With Tire Pressure Monitor (TPM) System U2150: Navigation Electronic Control Unit (ECU) Gateway Communications U2151: Navigation Electronic Control Unit (ECU) Communications U2152: Navigation Bus Request Line Circuit Low U2153: Navigation Electronic Control Unit (ECU) - VICS Communication Circuit U2160: Lost Communication With Steering Control System Sensor U2161: Lost Communication With Dash Integration Module (DIM) U2162: Lost Communication With Instrument Panel integration Module (IPM) U2163: Lost Communication With Left Rear Door Module (LRDM) U2164: Lost Communication With Right Rear Door Module (RRDM) U2165: Lost Communication With Driver Door Switch (DDS) U2166: Lost Communication With Driver Position Module (DPM) U2167: Lost Communication With Remote Control Door Lock Receiver U2168: Lost Communication With Side Object Detection (SOD) Module - Left U2169: Lost Communication With Side Object Detection (SOD) Module - Right U2170: Lost Communication With Four Wheel Drive (4WD) Clutch U2171: Lost Communication With Rear Seat Entertainment (RSE) U2172: Lost Communication With Digital Radio Receiver U2173: Lost Communication With Passive Entry and Passive Start System U2174: Lost Communication With Parking Heater System U2175: Lost Communication With Special Vehicle Module U2176: Lost Communication With Power Take Off (PTO) Control Module U2177: Lost Communication With Cruise Control Module U2178: Lost Communication With Trailer Interface Module U2179: Lost Communication With Television Module U2180: Lost Communication With Folding Top Control Module U2181: Lost Communication With Moveable Roof Module

DIAGNOSTIC CODE INDEX

Diagnostic Instructions

  1. Perform the «Diagnostic System Check - Vehicle»(ref-301515-S32423278442008101700000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-301515-S06578354042008101700000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-301515-S28090839972008101700000) provides an overview of each diagnostic category.

Conditions for Running the DTC

Ignition ON.

Conditions for Setting the DTC

The control module has detected an internal malfunction.

Action Taken When the DTC Sets

The control module refuses all additional inputs.

Conditions for Clearing the DTC

  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears in all of the modules except the sensing and diagnostic module (SDM), when the ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.
  3. If the code is set in the SDM it will never clear and the Air Bag indicator will remain illuminated.
  1. Perform the «Diagnostic System Check - Vehicle»(ref-301515-S32423278442008101700000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-301515-S06578354042008101700000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-301515-S28090839972008101700000) provides an overview of each diagnostic category.

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

The control module is not configured properly.

  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. Perform the «Diagnostic System Check - Vehicle»(ref-301515-S32423278442008101700000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-301515-S06578354042008101700000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-301515-S28090839972008101700000) provides an overview of each diagnostic category.

The control module microprocessor must be active/awake.

The KAM in the control 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. Perform the «Diagnostic System Check - Vehicle»(ref-301515-S32423278442008101700000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-301515-S06578354042008101700000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-301515-S28090839972008101700000) provides an overview of each diagnostic category.

The control module runs the program to detect an EEPROM checksum error after each wake-up. The only requirements are battery positive voltage and ground.

The control module retains an inverse copy of the digital value stored in certain blocks of memory in the EEPROM. The control 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 control module reverts to base operation values programmed for those blocks of data that have failed the check sum test.

  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the control module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.
  1. Perform the «Diagnostic System Check - Vehicle»(ref-301515-S32423278442008101700000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-301515-S06578354042008101700000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-301515-S28090839972008101700000) provides an overview of each diagnostic category.

The microprocessor runs a diagnostic program to detect an internal fault when power up is commanded. The only requirements are voltage and ground.

  1. The control module detects an internal write malfunction.
  2. The control module detects an internal checksum malfunction.

If equipped, the following module specific actions may occur

  1. The antilock brake system (ABS) indicator turns ON.
  2. The BRAKE warning indicator turns ON.
  3. The electronic brake control module (EBCM) disables the ABS/dynamic rear proportion (DRP)/traction control system (TCS).
  4. The driver information center (DIC) displays the power steering warning message No Steering Assist.
  5. The TCS indicator turns ON.
  1. A current DTC clears when the malfunction is no longer present.
  2. A history DTC clears when the control module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.
  1. Perform the «Diagnostic System Check - Vehicle»(ref-301515-S32423278442008101700000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-301515-S06578354042008101700000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-301515-S28090839972008101700000) provides an overview of each diagnostic category.

Circuit Description

Modules connected to the GMLAN serial data circuits 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.

  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 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.

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 GMLAN Device. Refer to «Scan Tool Does Not Communicate with High Speed GMLAN Device»(ref-301496-S05542796792008101700000) .
  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»(ref-301496-S05542796792008101700000) .
  1. Perform the «Diagnostic System Check - Vehicle»(ref-301515-S32423278442008101700000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-301515-S06578354042008101700000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-301515-S28090839972008101700000) provides an overview of each diagnostic category.

Conditions for Running the DTCs

  1. Supply voltage to the modules are in the normal operating range.
  2. The vehicle power mode requires serial data communications.

The module setting the DTC has attempted to establish communications on the GMLAN circuits more than 3 times.

  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 of 50, without a repeat of the malfunction.
  1. An intermittent condition is likely to be caused by a short on the high speed GMLAN serial data circuits.
  2. This DTC cannot be retrieved with a current status. Diagnosis is accomplished using the symptom «Scan Tool Does Not Communicate with High Speed GMLAN Device»(ref-301496-S05542796792008101700000) .
  3. Refer to «Data Link References»(ref-301496-S07997527592008101700000) for the specific modules using high speed GMLAN serial data.
  1. Perform the «Diagnostic System Check - Vehicle»(ref-301515-S32423278442008101700000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-301515-S06578354042008101700000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-301515-S28090839972008101700000) provides an overview of each diagnostic category.

Diagnostic Fault Information

CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Module B+U0100-U0299U0100-U0299
IgnitionU0100-U0299U0100-U0299
Module GroundU0100-U0299U0100-U0299
Accessory Wake Up Serial DataU1814U0100-U0299
High Speed GMLAN Serial Data Wake UpU2099U0100-U0299
High Speed GMLAN Serial Data (+)2U0100-U02992
High Speed GMLAN Serial Data (-)2U0100-U02992
Low Speed GMLAN Serial Data1U0100-U02991
1. Scan tool does not communicate with low speed GMLAN device 2. Scan tool does not communicate with high speed GMLAN device

The system voltage is between 9-16 volts.

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

Specific subsystems will not function.

  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 of 50, without a repeat of the malfunction.
  1. Use the DTC Descriptor list above to determine the module which is not communicating.
  2. If there are multiple non-communicating modules choose the one closest to the data link connector (DLC).
  3. Use «Data Link References»(ref-301496-S07997527592008101700000) to determine if the module uses high or low speed GMLAN serial data communications.
  4. Some modules may not have internal protection for specific voltage outputs and may open a battery positive voltage or ignition voltage source fuse. If a voltage input fuse is open and no short is found in that circuit, ensure that no module output voltage circuit is shorted to ground before replacing the module.
  5. This diagnostic can be used for any module that should communicate with high or low speed GMLAN serial data providing the vehicle is equipped with the option that uses that module.

Circuit/System Testing

  1. Using the DTC Descriptor and Diagnostic Aids above, determine the module that is not communicating.
  2. Ignition OFF, disconnect the harness connector of the module that is not communicating.
  3. Ignition ON, verify that a test lamp illuminates between the serial data communication enable circuit OR the accessory wakeup serial data circuit and ground. If the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.
  4. Test for less than 1 ohm between the module ground circuits and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  5. Ignition ON, verify that a test lamp illuminates between all battery positive voltage circuits and ground. If the test lamp does not illuminate, test the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the module.
  6. Verify that a test lamp illuminates between all ignition voltage circuits and ground. If the test lamp does not illuminate, test the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the module.
  7. Test for less than 1 ohm on the GMLAN serial data circuits between the non-communicating module and the module that displays the DTC. If greater than the specified range, test the serial data circuit for open/high resistance.
  8. If all circuits test normal, replace the module that is not communicating.
  1. Perform the «Diagnostic System Check - Vehicle»(ref-301515-S32423278442008101700000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-301515-S06578354042008101700000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-301515-S28090839972008101700000) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to Voltage
Battery Positive Voltage CircuitsU1866-U1899U1866-U1899
Ignition Voltage CircuitsU1866-U1899U1866-U1899
Module Ground CircuitsU1866-U1899

Modules connected to the CAN 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.

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

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 of 50, 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.
  1. Using the DTC Descriptor and Diagnostic Aids above, determine the module that is not communicating that should be tested.
  2. Ignition OFF, disconnect the harness connector of the module that is not communicating.
  3. Ignition ON, verify that a test lamp illuminates between all battery positive voltage circuits and ground. If the test lamp does not illuminate, repair the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the faulty module.
  4. Verify that a test lamp illuminates between all ignition voltage circuits and ground. If the test lamp does not illuminate, repair the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the faulty module.
  5. Test for less than 1 ohm of resistance between the module ground circuits and ground. If greater than 1 ohm, repair the ground circuit for open/high resistance.
  6. Test for less than 1 ohm of resistance in the CAN serial data circuit(s) between the non-communicating module and the module that displays the DTC. If greater than 1 ohm of resistance, test the CAN serial data circuit(s) for open/high resistance.
  7. If all circuits test normal, replace the module that is not communicating.
  1. Perform the «Diagnostic System Check - Vehicle»(ref-301515-S32423278442008101700000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-301515-S06578354042008101700000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-301515-S28090839972008101700000) provides an overview of each diagnostic category.

The GMLAN serial data circuits are controller area network (CAN) high 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. The GMLAN serial data circuits also communicate directly to the DLC connector. 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 a DTC will result.

  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. 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 High Speed GMLAN Device»(ref-301496-S05542796792008101700000) .
  2. An intermittent condition is likely to be caused by a short on the class 2 serial data circuit.
  1. Perform the «Diagnostic System Check - Vehicle»(ref-301515-S32423278442008101700000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-301515-S06578354042008101700000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-301515-S28090839972008101700000) provides an overview of each diagnostic category.

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, for each virtual network. The messages are also supervised and some periodic messages are used by the receiver module as an availability indication of the transmitter module.

DTC U2103 will set when fewer modules are detected on the buss before the modules can learn the other module IDs. If the communication buss is opened, or if the module power supply is lost when the vehicle is in the OFF power mode, and then placed in the RUN power mode, U2103 will set in specific modules.

  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. Diagnosis of this DTC is accomplished via the symptom, «Scan Tool Does Not Communicate with Low Speed GMLAN Device (Buss 1)»(ref-301496-S40026754112008101700000) or «Scan Tool Does Not Communicate with Low Speed GMLAN Device (Buss 2)»(ref-301496-S39816310512008101700000) .
  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 Low Speed GMLAN Device (Buss 1)»(ref-301496-S40026754112008101700000) or «Scan Tool Does Not Communicate with Low Speed GMLAN Device (Buss 2)»(ref-301496-S39816310512008101700000) procedure in order to isolate an intermittent condition.
  1. Perform the «Diagnostic System Check - Vehicle»(ref-301515-S32423278442008101700000) prior to using the diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-301515-S06578354042008101700000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-301515-S28090839972008101700000) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Low Speed GMLAN Serial Data1U2105-U21991
Battery Positive Voltage CircuitsU2105-U2199U2105-U2199
Ignition Voltage CircuitsU2105-U2199U2105-U2199
Module Ground CircuitsU2105-U2199U2105-U2199
Accessory Wake Up Serial DataU1814U2105-U2199
High Speed GMLAN Serial Data Wake UpU2099U2105-U2199
1. Scan tool does not communicate with low speed GMLAN device
  1. The system voltage is between 9-16 volts.
  2. The vehicle power mode requires serial data communication to occur.

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

The module uses a default value for the missing parameters.

  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 of 50, without a repeat of the malfunction.
  1. Use the DTC Descriptor list above to determine the module which is not communicating.
  2. If there are multiple non-communicating modules choose the one closest to the data link connector (DLC).
  3. Use «Data Link References»(ref-301496-S07997527592008101700000) to determine if the module uses high or low speed GMLAN serial data communications
  4. Some modules may not have internal protection for specific voltage outputs and may open a battery positive voltage or ignition voltage source fuse. If a voltage input fuse is open and no short is found in that circuit, ensure that no module output voltage circuit is shorted to ground before replacing the module.
  5. This diagnostic can be used for any module that should communicate with high or low speed GMLAN serial data providing the vehicle is equipped with the option that uses that module.
IMPORTANTIf more than one module is not communicating use Data Communication Schematics to determine which module is closest to the DLC. Start diagnostics with that module. Terminal and connector identifiers will be different depending on the individual module being tested. Use Schematic Reference and Connector End View Reference to determine which connector and terminal to access.
  1. Using the DTC Descriptor and Diagnostic Aids, determine the module that is not communicating that should be tested.
  2. Ignition OFF, disconnect the harness connector of the module that is not communicating.
  3. Test for less than 2 ohms between the module ground circuits and ground. If greater than specified, repair the ground circuit for an open.
  4. Ignition ON, verify that a test lamp illuminates between the high speed GMLAN serial data wake up circuit OR the accessory wake up serial data circuit and ground. If the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM.
  5. Ignition ON, verify that a test lamp illuminates between all battery positive voltage circuits and ground. If the test lamp does not illuminate, repair the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the faulty module.
  6. Verify that a test lamp illuminates between all ignition voltage circuits and ground. If the test lamp does not illuminate, repair the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the faulty module.
  7. Test for less than 1 ohm in the GMLAN serial data circuit(s) between the non-communicating module and the module that displays the DTC. If greater than specified, test the GMLAN serial data circuit(s) for open/high resistance.
  8. If all circuits test normal, replace the module that is not communicating.

Visual/Physical Inspection

  1. Inspect for aftermarket devices which could affect the operation of the systems. Refer to «Checking Aftermarket Accessories»(ref-301517-S04233661632008101700000) .
  2. Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.

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»(ref-301496-S25825101442008101700000)
  2. «Scan Tool Does Not Communicate with High Speed GMLAN Device»(ref-301496-S05542796792008101700000)
  3. «Scan Tool Does Not Communicate with Low Speed GMLAN Device (Buss 1)»(ref-301496-S40026754112008101700000) or «Scan Tool Does Not Communicate with Low Speed GMLAN Device (Buss 2)»(ref-301496-S39816310512008101700000)
  1. Perform the «Diagnostic System Check - Vehicle»(ref-301515-S32423278442008101700000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-301515-S06578354042008101700000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-301515-S28090839972008101700000) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
DLC B+11
DLC Ground1
1. Scan Tool Does Not Power Up
  1. 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.
  2. If the B+ circuit, ground circuits, and connections of the DLC are functioning properly, the malfunction must be due to the scan tool/CANdi module.
  1. Test for less than 2.0 ohms between the ground circuits terminal 4 of the DLC and ground, and terminal 5 of the DLC and ground. If greater than the specified range, test the ground circuit for an open/high resistance.
  2. Ignition ON, verify a test lamp illuminates between the B+ circuit terminal 16 at the DLC and ground. If the test lamp does not illuminate, test the voltage supply circuit for a short to ground or an open/high resistance.
  3. If all circuits test normal, refer to the scan tool/CANdi module user guide.
  1. Perform the «Diagnostic System Check - Vehicle»(ref-301515-S32423278442008101700000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-301515-S06578354042008101700000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-301515-S28090839972008101700000) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
High Speed GMLAN Serial Data (+)12*1
High Speed GMLAN Serial Data (-)12*1
Ground (DLC, terminal 5)1
Battery Positive Voltage (B+)11
*An open between the data link connector (DLC) and the first splice will only effect the communication with the scan tool. The vehicle modules will still communicate. No communication on any high speed GMLAN module An open in only one high speed GMLAN serial data circuit may allow degraded communication between the modules.
  1. Communication may be available between the BCM and the scan tool with the high speed GMLAN serial data system inoperative. This condition is due to the BCM using both the high and low speed GMLAN systems.
  2. Use the «Data Link References»(ref-301496-S07997527592008101700000) to identify the high speed GMLAN serial data modules.
  3. This test is used for a total high speed GMLAN communication failure. If only one module is not communicating and sets no DTC, ensure that the vehicle is equipped with the module, then use DTC U0100-U0299 for diagnostics.
  4. An open in the DLC ground circuit terminal 5 will allow the scan tool to operate and set up the vehicle on the tool and then not communicate with the vehicle. When the scan tool is to the point of communicating with the vehicle, a message on the scan tool will indicate "no CANdi module detected" and will not communicate.
  5. The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus. The following conditions may cause a total loss of high speed GMLAN data communication: A short between high speed GMLAN (+) and high speed GMLAN (-) circuits Any of the high speed GMLAN serial data circuits shorted to ground or voltage A module internal malfunction that causes a short to voltage or ground on the high speed GMLAN circuits
  1. Test for less than 1 ohm between the ground circuit terminal 5 of the DLC and ground. If greater than the specified range, test the ground circuit for open/high resistance.
  2. Ignition OFF, disconnect the X2 harness connector at the BCM.
  3. Test for less than 2 ohms on the serial data circuit between terminal 6 of the DLC and terminal 1 of the BCM. If greater than the specified range, test the serial data circuit for open/high resistance.
  4. Ignition OFF, disconnect the X3 and X4 harness connector at the BCM.
  5. Verify a test lamp illuminates between each ground circuit terminal of the BCM listed below and B+. X2 terminal 13 X3 terminal 12 X4 terminal E12 If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  6. Ignition ON, verify a test lamp illuminates between each B+ circuit terminal D12 of the BCM and ground. If the test lamp does not illuminate, test the B+ circuit for an open/high resistance or short to ground.
  7. Ignition ON, test for less than 1 volt between the serial data circuit terminal 6 of the DLC and ground, and terminal 14 of the DLC and ground. If greater than the specified range, test the serial data circuit for a short to voltage.
  8. Test for infinite resistance between the serial data circuit terminal 6 of the DLC and ground, and terminal 14 of the DLC and ground. If less than the specified value, test the serial data circuit for a short to ground.
  9. Test for infinite resistance between the serial data circuits terminal 6 and terminal 14 of the DLC. If less than the specified value, test the serial data circuits for a short between them.
  10. Connect the X2, X3, and X4 harness connectors at the BCM.
  11. Disconnect the appropriate harness connector at the ECM. RPO LZ4 - X1 RPO LY7 - X3 RPO HP7 - X3
  12. Attempt to communicate with the vehicle control interface module (VCIM). Communication should not be available. If communication is available, replace the ECM.
  13. Ignition OFF, disconnect the harness connector at the SGCM (RPO - HP7).
  14. Attempt to communicate with the VCIM. Communication should not be available. If communication is available, test the following serial data circuits for a short between the circuits, short to voltage, or a short to ground between the SGCM and the ECM. If the circuits test normal, replace the TCM. Terminal 11 Terminal 23
  15. Ignition OFF, disconnect the harness connector at the TCM.
  16. Attempt to communicate with the VCIM. Communication should not be available. If communication is available, test the following serial data circuits for a short between the circuits, short to voltage, or a short to ground between the TCM and the SGCM. If the circuits test normal, replace the TCM. RPO MH2 - 12 RPO MH2 - 5 RPO MH2 - 5 and 12 RPO MN5 - 37 RPO MN5 - 38 RPO MN5 - 37 and 38
  17. Ignition OFF, disconnect the harness connector at the EBCM.
  18. Attempt to communicate with the VCIM. Communication should not be available. If communication is available, test the following serial data circuits for a short between the circuits, short to voltage, or a short to ground between the EBCM and the TCM. If the circuits test normal, replace the EBCM. B12 B9
  19. Ignition OFF, disconnect the X2 harness connector at the power steering control module.
  20. Attempt to communicate with the VCIM. Communication should not be available. If communication is available, test the following serial data circuits for a short between the circuits, short to voltage, or a short to ground between the suspension control module and the terminator resistor. If the circuits test normal, replace the power steering control module. 1 2
  21. Ignition OFF, disconnect the X3 harness connector at the VCIM. Attempt to communicate with the BCM. Communication should not be available. If communication is available, test the following serial data circuits for a short between the circuits, short to voltage, or a short to ground between the VCIM and the suspension control module. If the circuits test normal, replace the VCIM. 9 8
  22. Ignition OFF, disconnect the X2 harness connector at the BCM.
  23. Ignition ON, test for less than 1 volt between the following serial data circuits of BCM and ground. 20 2 If greater than the specified range, test the circuit for a short to voltage.
  24. Test for infinite resistance between the following serial data circuits of BCM and ground. 20 2 If less than the specified value, test the circuit for a short to ground.
  25. Test for infinite resistance between the serial data circuits terminal 20 terminal 2 of the BCM. If less than the specified value, test the serial data circuits for a short between them.
  26. If the circuits test normal, replace the BCM.
  1. Perform the «Diagnostic System Check - Vehicle»(ref-301515-S32423278442008101700000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-301515-S06578354042008101700000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-301515-S28090839972008101700000) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Low Speed GMLAN Serial Data12*1
Ground (DLC, terminal 5)1
* An open between the data link connector (DLC) and X 203, or DLC ground terminal 5 will only effect the communication with the scan tool. The vehicle modules will still communicate. No communication on any low speed GMLAN module No communication on a specific low speed GMLAN module
  1. Use the «Data Link References»(ref-301496-S07997527592008101700000) to identify the low speed GMLAN serial data modules.
  2. This test is used for a total low speed GMLAN communication failure. If only 1 module is not communicating and sets no DTC, ensure that the vehicle is equipped with the module, then use DTC U0100-U0299 for diagnostics.
  3. An open in the low speed GMLAN serial data circuit between the splice pack (comb) and a module(s) will only effect the specific module(s). This type of failure will set a loss of communication DTC for each module effected, and the other modules will still communicate.
  4. An open in the DLC ground circuit terminal 5 will allow the scan tool to operate to set up the vehicle on the tool and then not communicate with the vehicle. When the scan tool is to the point of communicating with the vehicle, a message on the scan tool will indicate "no CANdi module detected" and will not communicate.
  5. An open between the data link connector (DLC) and X 203 will only effect the communication with the scan tool. The vehicle modules will still communicate, and the vehicle will start.
  6. The engine will not start when there is a total malfunction of the low speed GMLAN serial data circuit. The following conditions may cause a total loss of low speed GMLAN data communication: The low speed GMLAN serial data circuit shorted to ground or voltage. A module internal malfunction that causes a short to voltage or ground on the low speed GMLAN circuit. An open in the DLC ground circuit.
  7. Use the DMM MIN/MAX function to capture/locate intermittent conditions.
  1. Ignition OFF, test for less than 1.0 ohm between the DLC ground circuit terminal 5 and ground. If greater than specified, test the ground circuit for open/high resistance.
  2. Disconnect the X2 harness connector at the BCM.
  3. Install a 3A fused jumper wire between the BCM serial data circuit terminal 55 and the DLC terminal 1.
  4. Ignition ON, attempt to communicate with the BCM. Communication should be available. IMPORTANT: Allow communications for 5 seconds after connecting a module with the jumper to determine if communication is interrupted or not. If no communication, test the serial data circuit terminal 55 of the BCM for a short to ground, short to voltage, or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. Ignition OFF, install a 3A fused jumper wire between the BCM serial data circuit terminal 37 and the vehicle control interface module terminal 1.
  6. Disconnect the X1 harness connector at the radio, if applicable.
  7. Ignition ON, attempt to communicate with the theft deterrent control module (TDM), communication should not be available. If communication is established, test the radio serial data circuit terminal B10 for a short to voltage or a short to ground. If the circuit tests normal, replace the radio.
  8. Ignition OFF, disconnect the X2 harness connector at the HVAC control module, if applicable.
  9. Ignition ON, attempt to communicate with the TDM, communication should not be available. If communication is established, test the HVAC control module serial data circuit terminal 1 for a short to voltage or a short to ground. If the circuit test normal, replace the HVAC control module.
  10. Ignition OFF, disconnect the harness connector at the TDM.
  11. Ignition ON, attempt to communicate with the instrument panel cluster (IPC), communication should not be available. If communication is established, test the TDM serial data circuit terminal 6 for a short to voltage or a short to ground. If the circuit test normal, replace the TDM.
  12. Ignition OFF, disconnect the harness connector at the IPC.
  13. Ignition ON, attempt to communicate with the BCM, communication should not be available. If communication is established, test the IPC serial data circuit terminal A8 for a short to voltage or a short to ground. If the circuit test normal, replace the IPC.
  14. Ignition OFF, disconnect the X3 harness connector at the VCIM, if applicable.
  15. Ignition ON, attempt to communicate with the BCM, communication should not be available. If communication is established, test the VCIM serial data circuit terminal 7 for a short to voltage or a short to ground. If the circuit tests normal, replace the VCIM.
  16. Ignition OFF, remove the 3A fused jumper wire from the BCM terminal 37.
  17. Ignition ON, test for less then 1 volt between the BCM serial data circuit terminal 37 and ground. If greater then the specified range, test the serial data circuit for a short to voltage.
  18. Ignition OFF, test for less the 1 ohm between the BCM serial data circuit terminal 37 and ground. If greater than the specified range, test the circuit for a short to ground.
  19. If all circuits test normal, replace the BCM.
  1. Perform the «Diagnostic System Check - Vehicle»(ref-301515-S32423278442008101700000) prior to using this diagnostic procedure.
  2. Review «Strategy Based Diagnosis»(ref-301515-S06578354042008101700000) for an overview of the diagnostic approach.
  3. «Diagnostic Procedure Instructions»(ref-301515-S28090839972008101700000) provides an overview of each diagnostic category.
CircuitShort to GroundOpen/High ResistanceShort to VoltageSignal Performance
Low Speed GMLAN Serial Data12*1
Ground (DLC, terminal 5)1
* An open between the data link connector (DLC) and X 203, or DLC ground terminal 5 will only effect the communication with the scan tool. The vehicle modules will still communicate. No communication on any low speed GMLAN module No communication on a specific low speed GMLAN module
  1. Use the «Data Link References»(ref-301496-S07997527592008101700000) to identify the low speed GMLAN serial data modules.
  2. This test is used for a total low speed GMLAN communication failure. If only 1 module is not communicating and sets no DTC, ensure that the vehicle is equipped with the module, then use DTC U0100-U0299 for diagnostics.
  3. An open in the low speed GMLAN serial data circuit between the splice pack (comb) and a module(s) will only effect the specific module(s). This type of failure will set a loss of communication DTC for each module effected, and the other modules will still communicate.
  4. An open in the DLC ground circuit terminal 5 will allow the scan tool to operate to set up the vehicle on the tool and then not communicate with the vehicle. When the scan tool is to the point of communicating with the vehicle, a message on the scan tool will indicate "no CANdi module detected" and will not communicate.
  5. An open between the data link connector (DLC) and X 203 will only effect the communication with the scan tool. The vehicle modules will still communicate, and the vehicle will start.
  6. The engine will not start when there is a total malfunction of the low speed GMLAN serial data circuit. The following conditions may cause a total loss of low speed GMLAN data communication: The low speed GMLAN serial data circuit shorted to ground or voltage A module internal malfunction that causes a short to voltage or ground on the low speed GMLAN circuit An open in the DLC ground circuit
  7. Use the DMM MIN/MAX function to capture/locate intermittent conditions.
  1. Ignition OFF, test for less than 1.0 ohm between the DLC ground circuit terminal 5 and ground. If greater than specified, test the ground circuit for open/high resistance.
  2. Disconnect the X2 harness connector at the BCM.
  3. Install a 3A fused jumper wire between the BCM serial data circuit terminal 55 and the DLC terminal 1.
  4. Ignition ON, attempt to communicate with the BCM. Communication should be available. IMPORTANT: Allow communications for 5 seconds after connecting a module with the jumper to determine if communication is interrupted or not. If no communication, test the serial data circuit terminal 55 of the BCM for a short to ground, short to voltage, or an open/high resistance. If the circuit tests normal, replace the BCM.
  5. Ignition OFF, disconnect the X1 harness connector at the BCM.
  6. Ignition OFF, install a 3A fused jumper wire between the BCM serial data circuit terminal 55 and the inflatable restraint sensing and diagnostic module (SDM) terminal 2.
  7. Disconnect the X1 harness connector at the folding top control module, if applicable.
  8. Ignition ON, attempt to communicate with the SDM, communication should not be available. If communication is established, test the folding top control module serial data circuit terminal 2 for a short to voltage or a short to ground. If the circuit tests normal, replace the folding top control module.
  9. Ignition OFF, disconnect the harness connector at the digital radio receiver (DRR), if applicable.
  10. Ignition ON, attempt to communicate with the SDM, communication should not be available. If communication is established, test the DRR serial data circuit terminal 5 for a short to voltage or a short to ground. If the circuit test normal, replace the DRR.
  11. Ignition OFF, disconnect the harness connector at the RCDLR.
  12. Ignition ON, attempt to communicate with the SDM, communication should not be available. If communication is established, test the RCDLR serial data circuit terminal 2 for a short to voltage or a short to ground. If the circuit test normal, replace the RCDLR.
  13. Ignition OFF, disconnect the harness connector at the SDM.
  14. Ignition ON, attempt to communicate with the BCM, communication should not be available. If communication is established, test the SDM serial data circuit terminal 32 for a short to voltage or a short to ground. If the circuit test normal, replace the SDM.
  15. Ignition OFF, remove the 3A fused jumper wire from the BCM terminal 55.
  16. Ignition ON, test for less then 1 volt between the BCM serial data circuit terminal 55 and ground. If greater then the specified range, test the serial data circuit for a short to voltage.
  17. Ignition OFF, test for less the 1 ohm between the BCM serial data circuit terminal 55 and ground. If greater than the specified range, test the circuit for a short to ground.
  18. If all circuits test normal, replace the BCM.

The communication among control modules is performed through the GMLAN high speed serial data circuit and the GMLAN low speed 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 translate serial data messages between the GMLAN high speed buss and the GMLAN low speed buss. The gateway will interact with each network according to that network's transmission protocol. Refer to Body Control System Description and Operation for more information about the gateway.

GMLAN High Speed Circuit Description

IMPORTANTA loss of serial data DTC does not represent a failure of the module that the code is set in.

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 Kb/s. The twisted pair is terminated with two 120 ohms resistors, one is internal to the powertrain control module (PCM) or engine control module (ECM) depending on regular production option (RPO) and the other is internal to the body control module (BCM). The BCM is considered the DLC termination point of the link and the engine management controller is the other end of the link. The resistors are used to reduce noise on 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. The idle level, which is approximately 2.5 volts, is considered recessive transmitted data and is interpreted as a logic 1. Driving the lines to their extremes, adds one volt to the high speed GMLAN serial data bus (+) and subtracts one volt from the 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 vehicles 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.

GMLAN Low Speed Circuit Description

The data link connector (DLC) allows a scan tool to communicate with the low speed GMLAN serial data circuit. The serial data is transmitted over a single wire to the appropriate control modules. The transmission speed for GMLAN low speed is up to 83.33 Kb/s. Under normal vehicle operating conditions, the speed of the buss is 33.33 Kb/s. This protocol produces a simple pules train sent out over the GMLAN low speed serial data bus. When a module pulls the buss high, 5 volts, this creates a dominant logic state or 0 on the buss. When the buss is pulled low 0 volts, it is translated as a recessive logic state or 1. To wake the control modules connected to the GMLAN low speed serial data buss, a high voltage wake up pulse is sent out over the buss, the voltage level of the pulse is +10 volts. Modules connected to the GMLAN low speed buss can be part of a virtual network as described in the previous paragraph. The modules on the GMLAN low speed serial data buss are connected to the buss in a parallel configuration.

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