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Makes 🢒 Chevrolet 🢒 2008 🢒 Malibu 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Scan Tool Does Not Communicate with Low Speed GMLAN Device

Scan Tool Does Not Communicate with Low Speed GMLAN Device Buss 1

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Low Speed GMLAN Serial Data

1

2*

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.

1. No communication on any low speed GMLAN module

2. No communication on a specific low speed GMLAN module

Circuit/System Description

Modules connected to the low speed GMLAN serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules when the ignition switch is in any position other than OFF. The low speed GMLAN serial data circuit must be operational for the vehicle to start so the vehicle theft deterrent (VTD) module and body control module (BCM) can communicate. The low speed GMLAN serial data circuit uses JX 300 (splice pack comb) as a common connection between some modules and the DLC.

Diagnostic Aids
    • Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:
       - A control module on the data communication circuit was disconnected while the communication circuit is awake.
       - Power to one or more modules was interrupted during diagnosis
       - A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.
       - Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.
       - If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
    • Do not replace a control module reporting a U code. The U code identifies which control module needs to be diagnosed for a communication issue.
    • 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.
    • An open in the DLC ground circuit terminal 5 will allow the scan tool to operate but not communicate with the vehicle. When the scan tool attempts to communicate with the vehicle a message "no CANdi module detected" will be displayed.
    • The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus.
    • Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC) and no low speed GMLAN communications with the scan tool.
    • The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus.
        These conditions may be caused by the installation of an aftermarket navigation radio module (see bulletins). Some customers may comment of one or more of the following concerns:
       - Vehicle will not crank.
       - Vehicle cranks but will not start.
       - Vehicle stability enhancement system warning lights and messages.
       - PRNDL gear indicator position errors.
       - Tire Pressure Monitor (TPM) system warning lights.

Reference Information

Schematic Reference

    •  Data Communication Schematics
    •  Control Module References

Connector End View Reference

Component Connector End Views

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool References

Control Module References for scan tool information.

Circuit/System Testing
  1. Ignition OFF, test for less than 1.0 ohm between the DLC ground circuit terminal 5 and ground.
    2. ⇒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.

    5. 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.
    8. ⇒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.
    10. ⇒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.
    12. ⇒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.
    14. ⇒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.
    16. ⇒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.
    18. ⇒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.
    19. ⇒If greater than the specified range, test the circuit for a short to ground.
  19. If all circuits test normal, replace the BCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

    •  GMLAN Wiring Repairs
    •  Control Module References for module replacement, setup, and programming

Scan Tool Does Not Communicate with Low Speed GMLAN Device Buss 2

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Low Speed GMLAN Serial Data

1

2*

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.

1. No communication on any low speed GMLAN module

2. No communication on a specific low speed GMLAN module

Circuit/System Description

Modules connected to the low speed GMLAN serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules when the ignition switch is in any position other than OFF. The low speed GMLAN serial data circuit must be operational for the vehicle to start so the vehicle theft deterrent (VTD) module and body control module (BCM) can communicate. The low speed GMLAN serial data circuit uses JX 300 (splice pack comb) as a common connection between some modules and the DLC.

Diagnostic Aids
    • Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:
       - A control module on the data communication circuit was disconnected while the communication circuit is awake.
       - Power to one or more modules was interrupted during diagnosis
       - A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.
       - Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.
       - If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
    • Do not replace a control module reporting a U code. The U code identifies which control module needs to be diagnosed for a communication issue.
    • 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.
    • An open in the DLC ground circuit terminal 5 will allow the scan tool to operate but not communicate with the vehicle. When the scan tool attempts to communicate with the vehicle a message "no CANdi module detected" will be displayed.
    • The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus.
    • Technicians may find various Local Area Network (LAN) communication Diagnostic Trouble Codes (DTC) and no low speed GMLAN communications with the scan tool.
    • The engine will not start when there is a total malfunction of the high speed GMLAN serial data bus.
        These conditions may be caused by the installation of an aftermarket navigation radio module (see bulletins). Some customers may comment of one or more of the following concerns:
       - Vehicle will not crank.
       - Vehicle cranks but will not start.
       - Vehicle stability enhancement system warning lights and messages.
       - PRNDL gear indicator position errors.
       - Tire Pressure Monitor (TPM) system warning lights.

Reference Information

Schematic Reference

    •  Data Communication Schematics
    •  Control Module References

Connector End View Reference

Component Connector End Views

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool References

Control Module References for scan tool information.

Circuit/System Testing
  1. Ignition OFF, test for less than 1.0 ohm between the DLC ground circuit terminal 5 and ground.
    2. ⇒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.

    5. 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.
    9. ⇒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.
    11. ⇒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.
    13. ⇒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.
    15. ⇒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.
    17. ⇒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.
    18. ⇒If greater than the specified range, test the circuit for a short to ground.
  18. If all circuits test normal, replace the BCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

    •  GMLAN Wiring Repairs
    •  Control Module References for module replacement, setup, and programming