LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Cadillac >> 2011 >> Escalade EXT >> Repair and Diagnosis >> Engine Performance >> System >> Data Communications System >> Diagnostic Information and Procedures >> DTC U0074 >> Circuit/System Testing
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Circuit/System Testing

NOTE:

Each control module may need to be disconnected to isolate a circuit fault. Use the schematic to identify the following:

  • Control modules the vehicle is equipped with
  • Powertrain High Speed GMLAN serial data circuit terminating resistors
  • Control module locations on the Powertrain High Speed GMLAN serial data circuits
  • Each control module's Powertrain High Speed GMLAN serial data circuit terminals
  1. Attempt to communicate with all control modules on the Powertrain High Speed GMLAN serial data circuit, refer to Data Link References . Communications should not be available with two or more control modules on the Powertrain High Speed GMLAN serial data circuit.
    • If only one control module is not communicating, diagnose that control module only; refer to.
  2. Disconnect the scan tool from the DLC. The following tests will be done at the DLC connector.
  3. Ignition ON, test for less than 4.5 V between the serial data circuits listed below and ground:
    • Terminal 3
    • Terminal 11
    • If greater than the specified range, test the serial data circuit for a short to voltage; refer to Testing the Serial Data Circuits for a Short to Voltage below.
  4. Ignition OFF for 60 seconds, test for greater than 100 Ω between the serial data circuit listed below and ground:
    • Terminal 3
    • Terminal 11
    • If not the specified value, test the serial data circuit for a short to ground; refer to Testing the Serial Data Circuits for a Short to ground.
  5. Test for 50-70 Ω between the serial data circuit terminal 3 and terminal 11.
    • If less than 35 Ω, test for a short between the serial data circuits; refer to Testing the Serial Data Circuits for a Short between the Circuits.
    • If 35-50 Ω there may be a third terminating resistor between the serial data circuits. This can happen if the incorrect control module is installed. Some control modules are available with and without the terminating resistors installed to reduce the need of terminating resistors in the wiring harness.
    • If greater than 70 Ω but less than infinite, test the serial data circuit for an open/high resistance; refer to Testing the Serial Data Circuits for an Open/High Resistance.
    • If infinite, test the serial data circuits between the DLC and the first connection to the serial data circuit for an open/high resistance.

Testing the Serial Data Circuits for a Short to Voltage

  1. Ignition OFF, disconnect the harness connectors with the Powertrain High Speed GMLAN serial data circuits at an easily accessible control module.
  2. Ignition ON, test for greater than 4.5 V between each serial data circuit at the control module connector that was just disconnected and ground. Verify that one or more serial data circuits are greater than 4.5 V.
    • If all serial data circuits are less than the specified range, replace the control module that was disconnected.
  3. Ignition OFF, disconnect the harness connectors with the Powertrain High Speed GMLAN serial data circuits at another control module, in the direction of the circuit shorted to voltage.
  4. Ignition ON, test for greater than 4.5 V between the serial data circuits at the control module connector that was just disconnected and ground. Verify that one or more serial data circuits are greater than 4.5 V.
    • If all serial data circuits are less than the specified range, replace the control module that was just disconnected.
  5. Repeat step 3 until one of the follow conditions are isolated:
    • A short to voltage on the serial data circuit between 2 control modules
    • A short to voltage on the serial data circuit between a control module and a terminating resistor.

Testing the Serial Data Circuits for a Short to Ground

  1. Ignition OFF, disconnect the harness connectors with the Powertrain High Speed GMLAN serial data circuits at an easily accessible control module.
  2. Ignition OFF for 60 seconds, test for less than 1k Ω between each serial data circuit at the control module connector that was just disconnected and ground. Verify that one or more serial data circuits are less than 1k Ω.
    • If all serial data circuits are greater than the specified range, replace the control module that was disconnected.
  3. Disconnect the harness connectors with the Powertrain High Speed GMLAN serial data circuits at another control module, in the direction of the circuit shorted to ground.
  4. Ignition OFF for 60 seconds, test for less than 1k Ω between the serial data circuits at the control module connector that was just disconnected and ground. Verify that one or more serial data circuits are less than 1k Ω.
    • If greater than the specified range for all serial data circuits, replace the control module that was just disconnected.
  5. Repeat step 3 until one of the follow conditions are isolated:
    • A short to ground on the serial data circuit between 2 control modules
    • A short to ground on the serial data circuit between a control module and a terminating resistor.

Testing the Serial Data Circuits for a Short between the Circuits

  1. Ignition OFF, disconnect the harness connectors with the Powertrain High Speed GMLAN serial data circuits at an easily accessible control module that is not communicating.
  2. Ignition OFF for 60 seconds, test for less than 35 Ω between each pair of serial data circuits at the control module connector that was just disconnected. Verify that one pair of serial data circuits are less than 35 Ω.
    • If each pair of serial data circuits is greater than the specified range, replace the control module that was disconnected.
  3. Connect the harness connectors at the control module that was disconnected.
  4. Disconnect the harness connectors with the Powertrain High Speed GMLAN serial data circuits at another control module, in the direction of the circuits shorted together.
  5. Ignition OFF for 60 seconds, test for less than 35 Ω between each pair of serial data circuits at the control module connector that was just disconnected. Verify that one pair of serial data circuits are less than 35 Ω.
    • If each pair of serial data circuits is within the specified range, replace the control module that was just disconnected.
  6. Repeat step 3 until one of the following conditions are isolated:
    • Serial data circuits shorted together between 2 control modules
    • Serial data circuits shorted together between a control module and a terminating resistor
    • A shorted terminating resistor

Testing the Serial Data Circuits for an Open/High Resistance

  1. Ignition OFF, disconnect the harness connectors with the Powertrain High Speed GMLAN serial data circuits at an easily accessible control module that is not communicating.
  2. Ignition OFF for 60 seconds, test for greater than 100k Ω between each pair of serial data circuits at the control module connector that was just disconnected. Verify that one pair of serial data circuits are greater than 100k Ω.
    • If each pair of serial data circuits is less than the specified range, replace the control module that was disconnected.
  3. Connect the harness connectors at the control module that was disconnected.
  4. Disconnect the harness connectors with the Powertrain High Speed GMLAN serial data circuits at another control module, in the direction of the open circuit.
  5. Ignition OFF for 60 seconds, test for greater than 100k Ω between each pair of serial data circuits at the control module connector that was just disconnected. Verify that one pair of serial data circuits are greater than 100k Ω.
    • If each pair of serial data circuits is less than the specified range, replace the control module that was just disconnected.
  6. Repeat step 3 until one of the following conditions are isolated:
    • An open/high resistance on the serial data circuit between 2 control modules
    • An open/high resistance on the serial data circuit between a control module and a terminating resistor
    • An open/high resistance terminating resistor
scientia non olet · About LEMON Manuals