GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2008 🢒 XLR 🢒 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 60-ohm terminating resistors internal to the BCM and one 120-ohm terminating resistor internal to the ECM 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 malfunction. 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.
    • 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 data link connector (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 for diagnostics.
⇒If any high speed module communicates and no DTC beginning with a U exists, refer to DTC U0100-U0299 for diagnostics.

Circuit/System Testing

High Speed GMLAN Initial Test

  1. Test for less than 1.0 ohm of resistance between the DLC ground circuit terminal 5 and ground.
    2. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  2. Disconnect the harness connector at the TEHC module.
  3. Ignition ON, attempt to communicate with the ESC module.
    4. ⇒If communication is established refer to DIAGNOSTIC 2.
    ⇒If communication is not established, refer to DIAGNOSTIC 1.

DIAGNOSTIC 1

  1. Ignition OFF, disconnect the X2 harness connector at the BCM.
  2. Ignition OFF, test for less than 2 ohms of resistance between the DLC serial data circuit terminal 6 and BCM serial data circuit terminal 1.
    3. ⇒If greater than the specified range, test the serial data circuit for open/high resistance.
  3. Ignition OFF, disconnect the X1 and X4 harness connectors at the BCM.
  4. Test for less than 5 ohms of resistance between the following ground circuit terminals and ground.
    5. • X1 terminal 12
    • X4 terminal E12
    ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  5. Ignition OFF, disconnect the X3 harness connectors at the BCM.
  6. Ignition ON, verify a test lamp illuminates between the following B+ circuit terminals and ground.
    7. • X3 terminal D12
    • X3 terminal D1
    ⇒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.
  7. Ignition OFF, test for infinite resistance between the following serial data circuits of the DLC and ground.
    8. • Terminal 6
    • Terminal 14
    ⇒If less than the specified value, test the serial data circuits for a short to ground.
  8. Ignition ON, test for less than 1 volt between the following serial data circuits of the DLC and ground.
    9. • Terminal 6
    • Terminal 14
    ⇒If greater than the specified range, test the serial data circuit for a short to voltage.
  9. Ignition OFF, test for infinite resistance between the DLC serial data circuit terminal 6 and terminal 14.
    10. ⇒If less than the specified value, test for a short between the serial data circuits.
  10. Connect the X1, X2, X3 and X4 harness connector at the BCM.
  11. Ignition OFF, disconnect the harness connector at the ESC module.
  12. Ignition ON, attempt to communicate with the VCIM. Communication should not be available.
    13. ⇒If communication is established, test the following serial data circuits between the ESC module and the TECH for a short between the circuits, short to ground or a short to voltage. If the circuits test normal, replace the ESC module.
    • Terminal 40
    • Terminal 22
  13. Ignition OFF, disconnect the X4 harness connector at the VCIM if applicable.
  14. Ignition ON, attempt to communicate with the ACM. Communication should not be available.
    15. ⇒If communication is established, test the following serial data circuits between the VCIM and the ESC module for a short between the circuits, short to ground or a short to voltage. If the circuits test normal, replace the VCIM.
    • Terminal 2
    • Terminal 3
    • Terminal 2 and 3
  15. Ignition OFF, disconnect the harness connector at the ACM.
  16. Ignition ON, attempt to communicate with the BCM. Communication should not be available.
    17. ⇒If communication is established, test the following serial data circuits between the ACM and the VCIM for a short between the circuits, short to ground or a short to voltage. If the circuits test normal, replace the ACM.
    • Terminal 9
    • Terminal 8
    • Terminal 9 and 8
  17. Ignition OFF, disconnect the X2 harness connector at the BCM.
  18. Ignition OFF, test for infinite resistance between the following serial data circuits and ground.
    19. • Terminal 2
    • Terminal 20
    ⇒If less than the specified value, test the serial data circuit for a short to ground.
  19. Ignition ON, test for less than 1 volt between the following serial data circuits and ground.
    20. • Terminal 2
    • Terminal 20
    ⇒If greater than the specified range, test the serial data circuit for a short to voltage.
  20. Ignition OFF, test for infinite resistance between the serial data circuit terminal 2 and terminal 20.
    21. ⇒If less than the specified value, test for a short between the serial data circuits.
  21. If the circuits test normal, replace the BCM.

DIAGNOSTIC 2

  1. Connect the harness connector at the TEHC.
  2. Ignition OFF, disconnect the harness connector at the ECM.
  3. Ignition ON, attempt to communicate with the ESC module. Communication should not be available.
    4. ⇒If communication is established, replace the ECM.
  4. Ignition OFF, disconnect the harness connector at the EBCM.
  5. Ignition ON, attempt to communicate with the ESC module. Communication should not be available.
    6. ⇒If communication is established, test the following serial data circuits between the ECM and the EBCM for a short between the serial data circuits, short to ground or a short to voltage. If the circuits test normal replace the EBCM.
    • Terminal B9
    • Terminal B12
    • Terminal B9 and B12
  6. Ignition OFF, disconnect the jx168 inline harness connector.
  7. Ignition ON, attempt to communicate with the ESC module. Communication should not be available.
  8. If communication is established, test the following serial data circuits between the headlamp module and the EBCM and the headlamp module and the JX168 inline harness connector for a short between the serial data circuits, short to ground or a short to voltage.
    9. • Headlamp module terminal 2
    • Headlamp module terminal 5
    • Headlamp module terminal 2 and 5
    • Headlamp module terminal 3
    • Headlamp module terminal 4
    • Headlamp module terminal 3 and 4
    ⇒ If the circuits test normal replace the headlamp module.
  9. Ignition OFF, disconnect the harness connector at the TEHC module.
  10. Ignition ON, attempt to communicate with the ESC module. Communication should not be available.
  11. If communication is established, test the following serial data circuits between the TEHC module and the JX168 inline harness connector for a short between the serial data circuits, short to ground or a short to voltage.
    12. • Terminal 11
    • Terminal 10
  12. If the circuits test normal replace the TEHC module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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