GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2008 🢒 Malibu 🢒 Power and Signal Distribution 🢒 Data Communications 🢒 Scan Tool Does Not Communicate with High Speed GMLAN Device

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

High Speed GMLAN Serial Data (+)

1

2*

1

--

High Speed GMLAN Serial Data (-)

1

2*

1

--

Ground (DLC, terminal 5)

--

1

--

--

Battery Positive Voltage (B+)

1

1

--

--

*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.

1. No communication on any high speed GMLAN module

2. An open in only one high speed GMLAN serial data circuit may allow degraded communication between the modules.

Circuit/System Description

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 when the ignition switch is in any position other than OFF. The high speed GMLAN serial data circuits must be operational for the vehicle to start due to body control module (BCM) and engine control module (ECM) communications.

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 Reference

Control Module References for scan tool information

Circuit/System Testing
  1. Test for less than 1 ohm between the ground circuit terminal 5 of the DLC and ground.
    2. ⇒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.
    4. ⇒If greater than the specified range, test the serial data circuit for open/high resistance.
  4. Ignition OFF, disconnect the X1 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+.
    6. • X1 terminal 9
    • X1 terminal 12
    • X2 terminal 13
    • 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 the B+ circuit terminal D12 of the BCM and ground.
    7. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
  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.
    8. ⇒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.
    9. ⇒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.
    10. ⇒If less than the specified value, test the serial data circuits for a short between them.
  10. Connect the X1, X2, X3, and X4 harness connectors at the BCM.
  11. Disconnect the appropriate harness connector at the ECM.
    12. • RPO LZ4/LE5 - X1
    • RPO LY7 - X3
    • RPO HP7 - X3
  12. Attempt to communicate with the vehicle control interface module (VCIM). Communication should not be available.
    13. ⇒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.
    15. ⇒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 SGCM.
    • 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.
    17. ⇒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 - Terminal 12
    • RPO MH2 - Terminal 5
    • RPO MH2 - Terminal 5 and 12
    • RPO MN5 - Terminal 37
    • RPO MN5 - Terminal 38
    • RPO MN5 - Terminal 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.
    19. ⇒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.
    • Terminal B12
    • Terminal 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.
    21. ⇒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.
    • Terminal 1
    • Terminal 2
  21. Ignition OFF, disconnect the X3 harness connector at the VCIM. Attempt to communicate with the BCM. Communication should not be available.
    22. ⇒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.
    • Terminal 9
    • Terminal 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.
    24. • Terminal 20
    • Terminal 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.
    25. • Terminal 20
    • Terminal 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.
    26. ⇒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.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

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