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Home >> Buick >> 2012 >> Regal Base >> Repair and Diagnosis >> Engine Performance >> System >> Data Communications System >> Diagnostic Information and Procedures >> Scan Tool Does Not Communicate with Low Speed GMLAN Device >> Circuit/System Testing
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Circuit/System Testing

NOTE:

Use the schematic to identify the following:

  • Control modules the vehicle is equipped with
  • Control module and splice pack locations on the low speed GMLAN serial data circuit
  • The low speed GMLAN serial data circuit terminals for each control module, component, or splice pack
  1. Attempt to communicate with all control modules on the low speed GMLAN serial data circuit. Refer to Data Link References . Communications should not be available with two or more control modules on the low speed GMLAN serial data circuit.
    • If only one control module is not communicating, diagnose that control module only. Refer to DTC U0100-U02FF (without HP6) , DTC U0100-U02FF (with HP6) .
    • If one or more control modules are communicating but not all, refer to Testing the Serial Data Circuit for an Open/High Resistance.
  2. Disconnect the scan tool from the DLC. The following tests will be done at the DLC connector.
  3. All access doors closed, ignition OFF for 60 seconds, test for less than 10 Ω between the ground circuit terminal 5 and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  4. Ignition ON, test for less than 4.5 V between the serial data circuit terminal 1 and ground.
    • If greater than the specified range, test the serial data circuit for a short to voltage. Refer to Testing the Serial Data Circuit for a Short to Voltage.
  5. Ignition OFF for 60 seconds, test for greater than 100 Ω between the serial data circuit terminal 1 and ground.
    • If less than the specified range, test the serial data circuit for a short to ground. Refer to Testing the Serial Data Circuits for a Short to ground.
  6. Disconnect the harness connector at the first splice pack closest in the circuit to the DLC.
  7. Test for less than 2 Ω between the DLC serial data circuit terminal 1 and the splice pack connector serial data input terminal.
    • If greater than the specified range, test the serial data circuit for an open/high resistance. If the circuit tests normal, replace the splice pack.

Testing the Serial Data Circuits for a Short to Voltage

  1. Ignition OFF, disconnect the appropriate harness connectors at the following components:
    • All low speed serial data splice packs
    • Any module or component between that may be between the splice packs
  2. Ignition ON, test for less than 4.5 V between the DLC serial data circuit terminal 1 and ground.
    • If greater than the specified range, repair the short to voltage.
  3. Test for less than 4.5 V between each serial data circuit at each component connector and ground.
    • If greater than the specified range, perform the appropriate test listed below:
    • Serial data circuits with one control module, test the serial data circuit for a short to voltage. If the circuit tests normal, replace the control module.
    • Serial data circuits with 2 or more control modules, test each section of the serial data circuit for a short to voltage. If the circuits test normal, replace the control module that causes the short to voltage when connected.

Testing the Serial Data Circuits for a Short to Ground

  1. Ignition OFF, disconnect the appropriate harness connectors at the following components:
    • All low speed serial data splice packs
    • Any module or component between that may be between the splice packs
  2. Test for infinite resistance between the DLC serial data circuit terminal 1 and ground.
    • If not the specified value, repair the short to ground.
  3. Ignition OFF for 60 seconds, test for greater than 100 Ω between each serial data circuit at the splice pack and ground.
    • If less than the specified range, perform the appropriate test listed below:
    • Serial data circuits with one control module, test the serial data circuit for a short to ground. If the circuit tests normal, replace the control module.
    • Serial data circuits with 2 or more control modules, test each section of the serial data circuit for a short to ground. If the circuits test normal, replace the control module that causes the short to ground when connected.

Testing the Serial Data Circuit for an Open/High Resistance

  1. If equipped with a second splice pack, ignition ON, verify the scan tool communicates with one or more control modules connected to the second splice pack.
    • If all control modules on the second splice pack do not communicate, test the serial data circuit between the first and second splice packs for an open/high resistance. If the circuit tests normal, test the second splice pack for an open/high resistance. If the splice pack tests normal, replace any module or component that may be between those two splice packs.
  2. If equipped with a third splice pack, ignition ON, verify the scan tool communicates with one or more control modules connected to the third splice pack.
    • If all control modules on the third splice pack do not communicate, test the serial data circuit between the second and third splice packs for an open/high resistance. If the circuit tests normal, test the third splice pack for an open/high resistance. If the splice pack tests normal, replace any module or component that may be between the those two splice packs.
  3. Ignition OFF, disconnect the splice pack containing the serial data circuits to the modules that are not communicating.
  4. Install a 3 A fused jumper wire between the splice pack connector serial data input terminal and a low speed GMLAN serial data circuit that is not communicating:
  5. Ignition ON, verify the scan tool communicates with the control modules connected to the low speed GMLAN serial data circuit.
    • If any control module does not communicate, test each section of the serial data circuit for an open/high resistance. If the circuits test normal, replace the control module that does not communicate when connected.
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