GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2008 🢒 STS 🢒 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 Bus (+)

1

2¹

1

--

High Speed GMLAN Serial Data Bus (-)

1

2¹

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 will allow degraded communication between the modules.

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

With a scan tool, attempt to communicate with all High Speed GMLAN modules.

Circuit/System Testing
  1. With a scan tool verify that communication is not available for all high speed serial data modules.
    2. ⇒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 or U2105-U2199 .
  2. Ignition OFF, Test for less than 5 ohms between the DLC ground circuit terminal 5 and ground.
    3. ⇒If greater then the specified range, test the circuit for an open/high resistance.
  3. Ignition OFF, Test for less than 5 ohms between each IPM ground circuit and ground.
    4. ⇒If greater then the specified range, test the circuit for an open/high resistance.
  4. Ignition OFF, disconnect the harness connector of the IPM.
  5. Ignition ON, test for battery voltage between each voltage input circuit of the IPM and ground.
    6. ⇒If less than battery voltage, test each voltage output circuit of the IPM for a short to ground, and each voltage input circuit of the IPM for a short to ground or and open/high resistance. If the circuits test normal, replace the faulty module.
  6. Ignition OFF, Disconnect the appropriate harness connector at the ECM.
    7. • RPO LY7 - X2
    • RPO LH2 and LC3 - X3
  7. Attempt to communicate with the Distance Sensing Control Module, communication should not be available.
    8. ⇒If communication is established, replace the ECM.
  8. Ignition OFF, Disconnect the harness connector at the TCM.
  9. Attempt to communicate with the Distance Sensing Control Module, communication should not be available.
    10. ⇒If communication is established, test the serial data circuits for a short between them, short to ground or a short to voltage between the TCM and ECM. If the circuits test normal, replace the TCM.
  10. Ignition OFF, Disconnect the Harness connector at the EBCM.
  11. Attempt to communicate with the Distance Sensing Control Module, communication should not be available.
    12. ⇒If communication is established, test the serial data circuits for a short between them, short to ground or a short to voltage between the EBCM and the TCM. If the circuits test normal, replace the EBCM.
  12. Ignition OFF, Disconnect the harness connector at the Distance Sensing Control Module.
  13. Attempt to communicate with the VCIM, communication should not be available.
    14. ⇒If communication is established, replace the Distance Sensing Control Module.
  14. Ignition OFF, Disconnect the harness connector at the VCIM.
  15. Attempt to communicate with the ESC module, communication should not be available.
    16. ⇒If communication is established, test the serial data circuits for a short between them, short to ground or a short to voltage between the VCIM and Distance Sensing Control Module, and the VCIM and TCM. If the circuits test normal, replace the VCIM.
  16. Ignition OFF, Disconnect the harness connector at the ESC module.
  17. Attempt to communicate with the IPM , communication should not be available.
    18. ⇒If communication is established, test the serial data circuits for a short between them, short to ground or a short to voltage between the ESC module and the VCIM. If the circuit tests normal, replace the ESC.
  18. Ignition OFF, Disconnect the X3 harness connector at the IPM.
  19. Ignition OFF, Test for infinite resistance between the serial data circuits of IPM terminal 4 and ground, and between IPM terminal 5 and ground.
    20. ⇒If less than specified, test the circuit for a short to ground.
  20. Ignition ON, test for less than 1 volt between the serial data circuits of IPM terminal 4 and ground, and between IPM terminal 5 and ground.
    21. ⇒If greater than specified, test the circuit for a short to voltage
  21. Ignition OFF, test for infinite resistance between the serial data circuits of IPM terminal 4 terminal 5.
    22. ⇒If less than specified, test the serial data circuits for a short between the circuits.
  22. If the circuits test normal, replace the IPM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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