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For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2008 🢒 G8 🢒 Power and Signal Distribution 🢒 Data Communications 🢒 Scan Tool Does Not Communicate with High Speed GMLAN Device

Diagnostic Fault Information

Perform the Diagnostic System Check - Vehicle .

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

High speed GMLAN serial data bus (+)

1

2

1

--

High speed GMLAN serial data bus (-)

1

2

1

--

Ground (DLC, terminal 5)

--

1

--

--

  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 buss uses two 120-ohm terminating resistors that are in parallel with the high speed GMLAN (+) and (-) circuits. One of the resistors is in the instrument panel harness and the other is internal to the ECM.

Diagnostic Aids
    • 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 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.
    • 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
    • Use the DMM MIN/MAX function to capture/locate intermittent conditions.

Reference Information

Schematic Reference

    •  Data Communication Schematics
    •  Control Module References

Connector End View Reference

Master Electrical Component List

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 ground circuit terminal 5 at the DLC and ground.
    2. ⇒If greater than 1.0 ohm, test the ground circuit for open/high resistance.
  2. Remove the terminating resistor.
  3. Test for 110-130 ohms between the terminals at the terminating resistor.
    4. ⇒If not within the specified range, replace the terminating resistor.
  4. Connect the terminating resistor.
  5. Ignition OFF, disconnect the harness connector X3 at the BCM.
  6. Test for less than 2 ohms on the serial data circuit between terminal 6 of the DLC and harness connector X3, terminal 8 at the BCM.
    7. ⇒ If greater than the specified range, test the serial data circuit for open/high resistance.
  7. Verify a test lamp illuminates between each ground circuit terminal of the BCM listed below and B+.
    8. • X3 terminal 1
    • X3 terminal 5
    ⇒ If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
  8. Ignition OFF, disconnect the harness connectors X1 and X3 at the BCM.
  9. Ignition ON, verify a test lamp illuminates between each B+ circuit terminal of the BCM listed below and ground.
    10. • X1 terminal 14
    • X1 terminal 21
    • X3 terminal 3
    ⇒If the test lamp does not illuminate, test the appropriate B+ circuit for an open/high resistance or short to ground.
  10. Ignition OFF, disconnect the harness connector at the EBCM (except 6L80 transmission) or TCM (6L80 transmission).
  11. Ignition ON, test for less than 1 volt between the serial data circuit terminal 6 at the DLC and ground, and terminal 14 at the DLC and ground.
    12. ⇒If greater than the specified range, test the serial data circuit for a short to voltage.
  12. Test for infinite resistance between the serial data circuit terminal 6 at the DLC and ground, and terminal 14 at the DLC and ground.
    13. ⇒If less than the specified value, test the serial data circuit for a short to ground.
  13. Test for infinite resistance between the serial data circuits terminal 6 and terminal 14 at the DLC.
    14. ⇒If less than the specified value, test the serial data circuits for a short between the circuits.
  14. Connect the harness connectors at the BCM and the EBCM (except 6L80 transmission) or TCM (6L80 transmission).
  15. Disconnect the harness connector X3 at the ECM.
  16. Attempt to communicate with the BCM. Communication should not be available.
    17. ⇒If communication is available, replace the ECM.
  17. Ignition OFF, disconnect the harness connector X1 at the TCM (6L80 transmission) or harness connector X1 at the EBCM (except 6L80 transmission).
  18. Attempt to communicate with the BCM. Communication should not be available.
    19. ⇒If communication is available, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the TCM (6L80 transmission) or EBCM (except 6L80 transmission) and the ECM. If the circuits test normal, replace the TCM (6L80 transmission) or EBCM (except 6L80 transmission).
  19. Ignition OFF, disconnect the harness connector at the EBCM (6L80 transmission) or TCM (except 6L80 transmission).
  20. Attempt to communicate with the BCM. Communication should not be available.
  21. If communication is available, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the EBCM ( 6L80 transmission) or TCM (except 6L80 transmission) and the TCM (6L80 transmission) or EBCM (except 6L80 transmission). If the circuits test normal, replace the EBCM (6L80 transmission) or TCM (except 6L80 transmission).
  22. Ignition OFF, connect the harness connectors at the EBCM, TCM and ECM.
  23. Ignition OFF, disconnect the harness connector at the steering angle sensor. Attempt to communicate with the EBCM. Communication should not be available.
    24. ⇒If communication is available, test the serial data circuits for a short between the circuits, short to voltage, or a short to ground between the steering angle sensor and the terminator resistor. If the circuits test normal, replace the steering angle sensor.
  24. Ignition OFF, disconnect the harness connector X3 at the BCM.
  25. 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.
    26. ⇒If greater than the specified range, test the circuit for a short to voltage.
  26. Test for infinite resistance between the serial data circuits at BCM terminal 8 and ground, and between BCM terminal 9 and ground.
    27. ⇒If less than the specified value, test the circuit for a short to ground.
  27. Test for infinite resistance between the serial data circuits terminal 8 terminal 9 at the BCM.
    28. ⇒If less than the specified value, test the serial data circuits for a short between them.
  28. If the circuits test normal, replace the BCM.

Repair Instructions

Perform the Diagnostic Repair Verification .

    •  Control Module References
    •  GMLAN Wiring Repairs