GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 HUMMER 🢒 2008 🢒 H2 🢒 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. The vehicle theft deterrent (VTD) module and ECM exchange information using the BCM as the gateway module allowing communication between the high and low speed serial data busses. The low speed GMLAN serial data circuit must also be operational for vehicle starting. The high speed GMLAN serial data bus uses two 120 ohm terminating resistors that are in parallel with the high speed GMLAN (+) and (-) circuits.

Diagnostic Aids
    • 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.
    • Use the Data Link References to identify the high speed GMLAN serial data modules.
    •  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.
    • 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.
    • 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

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

Circuit/System Testing
  1. Test for less than 1.0 ohm between the DLC ground circuit terminal 5 and ground.
    2. ⇒If greater than the specified range, test the ground circuit for open/high resistance.
  2. Remove the terminator resistor.
  3. Test for 110-130 ohms between the terminals of the resistor.
    4. ⇒If not within the specified range, replace the resistor.
  4. Connect the terminator resistor.
  5. Ignition OFF, disconnect the harness connector X3 of the BCM.
  6. Test for less than 2 ohms of resistance in the GMLAN serial data circuit between the DLC terminal 6 and BCM terminal 16.
    7. ⇒If greater than specified, test the GMLAN serial data circuit for open/high resistance.
  7. Ignition OFF, disconnect the harness connector X4 of the BCM.
  8. Verify a test lamp illuminates between each ground circuit terminal of the BCM listed below and B+.
    9. • X3 terminal 1
    • X3 terminal 5
    • X4 terminal 9
    ⇒If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  9. Ignition ON, verify a test lamp illuminates between each B+ circuit terminal of the BCM listed below and ground.
    10. • X4 terminal 1
    • X4 terminal 3
    • X4 terminal 4
    ⇒If the test lamp does not illuminate, test the B+ circuit for an open/high resistance or short to ground.
  10. Ignition OFF, disconnect the harness connector of the vehicle communication interface module (VCIM).
  11. Test for infinite resistance between the high speed GMLAN serial data circuit of the DLC terminal 6 and ground, and terminal 14 and ground.
    12. ⇒If less than the specified range, test the serial data circuit for a short to ground.
  12. Ignition ON, test for less than 1 volt between the high speed GMLAN serial data circuit of the DLC terminal 6 and ground, and terminal 14 and ground.
    13. ⇒If greater than the specified range, test the serial data circuit for a short to voltage.
  13. Test for infinite resistance between the high speed GMLAN serial data circuits of the DLC terminal 6 and 14.
    14. ⇒If less than the specified range, test the serial data circuits for a short between them.
  14. Connect the harness connectors of the BCM and the VCIM.
  15. Disconnect the harness connector of the air suspension control module (ASCM).
  16. Attempt to communicate with the BCM. Communication should not be available.
    17. ⇒If communication is established, Test the serial data circuits between the ASCM and the terminator resistor for a short to ground, short to voltage, and a short between them. If the circuits test normal, replace the ASCM.
  17. Ignition OFF, disconnect the harness connector of the fuel pump flow control module (FPCM).
  18. Attempt to communicate with the BCM. Communication should not be available.
    19. ⇒If communication is established, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the FPCM and the ASCM. If the circuits test normal, replace the FPCM.
  19. Ignition OFF, disconnect the harness connector X2 of the electronic brake control module (EBCM).
  20. Attempt to communicate with the BCM. Communication should not be available.
    21. ⇒If communication is established, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the EBCM and the FPCM. If the circuits test normal, replace the EBCM.
  21. Ignition OFF, disconnect the harness connector X1 of the transfer case control module (TCCM).
  22. Attempt to communicate with the BCM. Communication should not be available.
    23. ⇒If communication is established, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the TCCM and the EBCM. If the circuits test normal, replace the TCCM.
  23. Ignition OFF, disconnect the harness connector X1 of the VCIM.
  24. Attempt to communicate with the BCM. Communication should not be available.
    25. ⇒If communication is established, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the VCIM and the TCCM. If the circuits test normal, replace the VCIM.
  25. Ignition OFF, connect the harness connectors of disconnected modules.
  26. Ignition OFF, disconnect the harness connector X1 of the ECM.
  27. Attempt to communicate with the BCM. Communication should not be available.
    28. ⇒If communication is established, replace the ECM.
  28. Ignition OFF, disconnect the harness connector of the transmission control module (TCM). Attempt to communicate with the BCM. Communication should not be available.
    29. ⇒If communication is established, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the TCM and the ECM. If the circuits test normal, replace the TCM.
  29. Ignition OFF, disconnect the harness connector X3 of the BCM.
  30. Test for infinite resistance between the serial data circuits of BCM terminal 8 and ground, and between BCM terminal 9 and ground.
    31. ⇒If less than the specified range, test the circuit for a short to ground.
  31. Ignition ON, test for less than 1 volt between the serial data circuits of BCM terminal 8 and ground, and between BCM terminal 9 and ground.
    32. ⇒If greater than the specified range, test the circuit for a short to voltage.
  32. Test for infinite resistance between the serial data circuits of BCM terminal 8 terminal 9.
    33. ⇒If less than the specified range, test the serial data circuits for a short between them.
  33. If the circuits test normal, replace the BCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

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