GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2008 🢒 CTS 🢒 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

Battery Positive Voltage (B+)

1

1

--

--

Ground (DLC, terminal 5)

--

1

--

--

High Speed GMLAN Serial Data (+)

1

2*

1

--

High Speed GMLAN Serial Data (-)

1

2*

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 buses. 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. One of the resistors is in the rear cargo area and the other is internal to the ECM.

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 malfunction. 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.
    • 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.
    • 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

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 Verification

Attempt to communicate with all modules on the high speed GMLAN bus.

⇒If any high speed module communicates and any DTC beginning with a U exists, refer to Diagnostic Trouble Code (DTC) List - Vehicle.
⇒If any high speed module communicates and no DTC beginning with a U exists, refer to DTC U0100-U0299.

Circuit/System Testing

High Speed GMLAN Initial Test

  1. Ignition OFF, test for less than 1.0 Ω between the data link connector (DLC) ground circuit terminal 5 and ground.
    2. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  2. If equipped, disconnect the X1 harness connector at the transfer case control module (TCC).
  3. Ignition ON, attempt to communicate with the vehicle control interface module (VCIM).
    4. ⇒If communication is established refer to DIAGNOSTIC 2.
    ⇒If communication is not established, refer to DIAGNOSTIC 1.

DIAGNOSTIC 1

  1. Connect the harness connector at the TCC module.
  2. Remove the terminator resistor.
  3. Test for 108-132 Ω between terminals A and B of the terminator resistor.
    4. ⇒If not within the specified range, replace the resistor.
  4. Connect the harness connector at the terminator resistor.
  5. Ignition OFF, disconnect the X3 harness connector at the BCM.
  6. Ignition OFF, test for less than 2 Ω between the DLC serial data circuit terminal 6 and BCM serial data circuit terminal 16.
    7. ⇒If greater than the specified range, test the serial data circuit for open/high resistance.
  7. Ignition OFF, disconnect the X4 harness connectors at the BCM.
  8. Test for less than 5 Ω between the following ground circuit terminals and ground.
    9. • X3 terminal 1
    • X3 terminal 5
    • X4 terminal 9
    ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  9. Ignition ON, verify a test lamp illuminates between the following B+ circuit terminals and ground.
    10. • X2 terminal 2
    • X3 terminal 2
    • X3 terminal 3
    • X4 terminal 1
    • X4 terminal 2
    • X4 terminal 3
    • X4 terminal 4
    • X4 terminal 10
    ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the B+ output circuits for a short to ground.
  10. Ignition OFF, test for infinite resistance between the following serial data circuits of the DLC and ground.
    11. • Terminal 6
    • Terminal 14
    ⇒If less than the specified value, test the serial data circuits for a short to ground.
  11. Ignition ON, test for less than 1-volt between the following serial data circuits of the DLC and ground.
    12. • Terminal 6
    • Terminal 14
    ⇒If greater than the specified range, test the serial data circuit for a short to voltage.
  12. Ignition OFF, test for infinite resistance between the DLC serial data circuit terminal 6 and terminal 14.
    13. ⇒If less than the specified value, test for a short between the serial data circuits.
  13. Connect the X3 and X4 harness connector at the BCM.
  14. Ignition OFF, disconnect the harness connector at the VCIM.
  15. Ignition ON, attempt to communicate with the TCC module. Communication should not be available.
    16. ⇒Replace the VCIM.
  16. Ignition OFF, disconnect the harness connector at the noise filter.
  17. Ignition ON, attempt to communicate with the TCC module. Communication should not be available.
    18. ⇒If communication is established, test the following serial data circuits between the noise filter and the VCIM, and the noise filter and the terminator resistor for a short between the circuits, short to ground or a short to voltage. If the circuits test normal, replace the noise filter.
    • Noise filer terminal 3 VCIM terminal 28
    • Noise filter terminal 4 VCIM terminal 14
    • Noise filter terminal 3 and terminal 4
    • Noise filter terminal 3 terminator resistor terminal A
    • Noise filter terminal 4 terminator resistor terminal B
  18. Ignition OFF, disconnect the X3 harness connector at the BCM.
  19. Ignition OFF, test for infinite resistance between the following serial data circuits and ground.
    20. • Terminal 16
    • Terminal 17
    ⇒If less than the specified value, test the serial data circuit for a short to ground.
  20. Ignition ON, test for less than 1-volt between the following serial data circuits and ground.
    21. • Terminal 16
    • Terminal 17
    ⇒If greater than the specified range, test the serial data circuit for a short to voltage.
  21. Ignition OFF, test for infinite resistance between the serial data circuit terminal 16 and terminal 17.
    22. ⇒If less than the specified value, test for a short between the serial data circuits.
  22. If the circuits test normal, replace the BCM.

DIAGNOSTIC 2

  1. Connect the harness connector at the TCC module.
  2. Ignition OFF, disconnect the harness connector the ECM.
  3. Ignition ON, attempt to communicate with the VCIM. Communication should not be available.
    4. ⇒If communication is established, replace the ECM.
  4. Ignition OFF, disconnect the harness connector at the transmission control module (TCM).
  5. Ignition ON, attempt to communicate with the VCIM. Communication should not be available.
    6. ⇒If communication is established, test the following serial data circuits between the ECM and the TCM for a short between the circuits, short to ground or a short to voltage. If the circuits test normal replace the EBCM.
    • Terminal 13
    • Terminal 14
  6. Ignition OFF, disconnect the harness connector at the electronic brake control module (EBCM).
  7. Ignition ON, attempt to communicate with the VCIM. Communication should not be available.
    8. ⇒If communication is established, test the following serial data circuits between the TCM and the EBCM for a short between the circuits, short to ground or a short to voltage. If the circuits test normal replace the EBCM.
    • Terminal 24
    • Terminal 37
  8. Ignition OFF, disconnect the harness connector at the headlamp leveling module.
  9. Ignition ON, attempt to communicate with the VCIM. Communication should not be available.
    10. ⇒If communication is established, test the following serial data circuits between the EBCM and the headlamp leveling module for a short between the circuits, short to ground or a short to voltage. If the circuits test normal replace the headlamp leveling module.
    • Terminal 7
    • Terminal 8
  10. Ignition OFF, disconnect the X1 harness connector at the pedestrian impact protection (PIP) module.
  11. Ignition ON, attempt to communicate with the VCIM. Communication should not be available.
    12. ⇒If communication is established, test the following serial data circuits between the PIP module and the headlamp leveling module for a short between the circuits, short to ground or a short to voltage. If the circuits test normal replace the PIP module.
    • Terminal 35
    • Terminal 37
  12. Ignition OFF, disconnect the X1 harness connector at the TCC module.
  13. Ignition ON, attempt to communicate with the VCIM. Communication should not be available.
    14. ⇒If communication is established, test the following serial data circuits between the TCC module and the PIP module for a short between the circuits, short to ground or a short to voltage. If the circuits test normal replace the TCC module.
    • Terminal 7
    • Terminal 8
  14. Ignition OFF, disconnect the harness connector at the BCM.
  15. Ignition OFF, test for infinite resistance between the following serial data circuits of BCM and ground.
    16. • Terminal 8
    • Terminal 9
    ⇒If less than the specified value, test the serial data circuit for a short to ground.
  16. Ignition ON, test for less than 1-volt between the following serial data circuits of BCM and ground.
    17. • Terminal 8
    • Terminal 9
    ⇒If greater than the specified range, test the serial data circuit for a short to voltage.
  17. Ignition OFF, test for infinite resistance between the BCM serial data circuit terminals 8 and 9.
    18. ⇒If less than the specified value, test for a short between the serial data circuits.
  18. If all circuits test normal, replace the BCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for control module replacement, setup, and programming