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Home >> Chevrolet >> 2019 >> Express 2500 Base, Van Cargo Extended, 2.8L Eng VIN 1 >> Repair and Diagnosis >> Engine Performance >> System >> Data Communications System >> Diagnostic Information and Procedures >> DTC U0077 >> Circuit/System Testing
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Circuit/System Testing

NOTE:

Each device may need to be disconnected to isolate a circuit fault. Use the wiring schematics and connector end views to identify the following:

  • Chassis high speed GMLAN devices and terminating resistors the vehicle is equipped with
  • Device locations on the chassis high speed GMLAN serial data circuits
  • Each device's ground, B+, ignition, and chassis high speed GMLAN serial data circuit terminals
NOTE:

Circuit/System Verification must be performed before proceeding with Circuit/System Testing.

Serial Data Starting Point

  1. Ignition/Vehicle OFF. Disconnect the harness connector at the B99 Steering Wheel Angle Sensor.
  2. Ignition ON/Vehicle In Service Mode.
  3. Test for less than 4.5 V between each of the chassis high speed GMLAN serial data circuit terminals listed below and ground:
    • Terminal 1
    • Terminal 2
    • Terminal 3
    • Terminal 4
    • If 4.5 V or greater between terminal 1 or terminal 3 and ground 
    1. Ignition/Vehicle OFF, disconnect the harness connector at the K17 Electronic Brake Control Module.
    2. Test for less than 1 V between each of the chassis high speed GMLAN serial data circuit terminals and ground at the B99 Steering Wheel Angle Sensor.
      • If 1 V or greater, repair the short to voltage in the circuit.
      • If less than 1 V, replace the K17 Electronic Brake Control Module.
    • If 4.5 V or greater between terminal 2 or terminal 4 and ground 
    1. Ignition/Vehicle OFF, disconnect the harness connector at the B176 Multi-axis Acceleration Sensor Module.
    2. Test for less than 1 V between each of the chassis high speed GMLAN serial data circuit terminals and ground at the B99 Steering Wheel Angle Sensor.
      • If 1 V or greater, repair the short to voltage in the circuit.
      • If less than 1 V, replace the B176 Multi-axis Acceleration Sensor Module.
    • Go to next step: If less than 4.5 V 
  4. Ignition/Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 10 min for all vehicle systems to power down.
  5. Test for greater than 100 Ω between each of the chassis high speed GMLAN serial data circuit terminals listed below and ground:
    • Terminal 1
    • Terminal 2
    • Terminal 3
    • Terminal 4
    • If 100 Ω or less between terminal 1 or terminal 3 and ground 
    1. Ignition/Vehicle OFF, disconnect the harness connector at the K17 Electronic Brake Control Module.
    2. Test for infinite resistance between each of the chassis high speed GMLAN serial data circuit terminals and ground at the B99 Steering Wheel Angle Sensor.
      • If less than infinite resistance, repair the short to ground in the circuit.
      • If infinite resistance, replace the K17 Electronic Brake Control Module.
    • If 100 Ω or less between terminal 2 or terminal 4 and ground 
    1. Ignition/Vehicle OFF, disconnect the harness connector at the B176 Multi-axis Acceleration Sensor Module.
    2. Test for infinite resistance between each of the chassis high speed GMLAN serial data circuit terminals and ground at the B99 Steering Wheel Angle Sensor.
      • If less than infinite resistance, repair the short to ground in the circuit.
      • If infinite resistance, replace the B176 Multi-axis Acceleration Sensor Module.
    • Go to next step: If greater than 100 Ω 
  6. Test for 110 - 130 Ω between each pair of the chassis high speed GMLAN serial data circuit terminals listed below.
    • Terminal 1 and terminal 3
    • Terminal 2 and terminal 4
    • If less than 110 Ω between terminal 1 and terminal 3 
    1. Ignition/Vehicle OFF, disconnect the harness connector at the K17 Electronic Brake Control Module.
    2. Test for infinite resistance between the chassis high speed GMLAN serial data circuit terminal 1 and terminal 3 at the B99 Steering Wheel Angle Sensor.
      • If less than infinite resistance, repair the short between the circuits.
      • If infinite resistance, replace the K17 Electronic Brake Control Module.
    • If less than 110 Ω between terminal 2 and terminal 4 
    1. Ignition/Vehicle OFF, disconnect the harness connector at the B176 Multi-axis Acceleration Sensor Module.
    2. Test for infinite resistance between the chassis high speed GMLAN serial data circuit terminal 1 and terminal 3 at the B99 Steering Wheel Angle Sensor.
      • If less than infinite resistance, repair the short between the circuits.
      • If infinite resistance, replace the B176 Multi-axis Acceleration Sensor Module.
    • If greater than 130 Ω between terminal 1 and terminal 3 
    1. Ignition/Vehicle OFF, disconnect the harness connector at the K17 Electronic Brake Control Module.
    2. Test for less than 2 Ω in each of the chassis high speed GMLAN serial data circuits end to end between the B99 Steering Wheel Angle Sensor and the K17 Electronic Brake Control Module.
      • If greater than 2 Ω, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K17 Electronic Brake Control Module.
    • If greater than 130 Ω between terminal 2 and terminal 4 
    1. Ignition/Vehicle OFF, disconnect the harness connector at the B176 Multi-axis Acceleration Sensor Module.
    2. Test for less than 2 Ω in each of the chassis high speed GMLAN serial data circuits end to end between the B99 Steering Wheel Angle Sensor and the B176 Multi-axis Acceleration Sensor Module.
      • If greater than 2 Ω, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the B176 Multi-axis Acceleration Sensor Module.
    • Go to next step: If between 110 - 130 Ω 
  7. Replace the B99 Steering Wheel Angle Sensor.

Testing the Device Circuits

  1. Ignition/Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 10 min for all vehicle systems to power down. Disconnect the harness connector at an easily accessible device that is not communicating.
  2. Test for less than 10 Ω between each of the ground circuit terminals and ground.
    • If 10 Ω or greater 
    1. Ignition/Vehicle OFF.
    2. Test for less than 2 Ω in the ground circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, repair the open/high resistance in the ground connection.
    • Go to next step: If less than 10 Ω 
  3. Ignition ON/Vehicle In Service Mode.
  4. If equipped, verify a test lamp illuminates between each of the B+ circuit terminals and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Ignition/Vehicle OFF, remove the test lamp.
    2. Test for less than 2 Ω in the B+ circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Ignition/Vehicle OFF, remove the test lamp.
    2. Test for infinite resistance between the B+ circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the disconnected device.
    • Go to next step: If the test lamp illuminates 
  5. If equipped, verify a test lamp illuminates between each of the ignition circuit terminals, which has a fuse in the circuit, and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Ignition/Vehicle OFF, remove the test lamp.
    2. Test for less than 2 Ω in the ignition circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, verify the fuse is OK and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Ignition/Vehicle OFF, remove the test lamp.
    2. Test for infinite resistance between the ignition circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance, replace the disconnected device.
    • Go to next step: If the test lamp illuminates 
  6. If equipped, verify a test lamp illuminates between each of the ignition circuit terminals, which is controlled by a control module, and ground.
    • If the test lamp does not illuminate 
    1. Ignition/Vehicle OFF, remove the test lamp, disconnect the harness connectors at the control module that controls the ignition circuit.
    2. Test for infinite resistance between the ignition circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    3. Test for less than 2 Ω in the ignition circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the control module that controls the ignition circuit.
    • Go to next step: If the test lamp illuminates 
  7. Ignition/Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 10 min for all vehicle systems to power down.
  8. Disconnect the harness connector at the K17 Electronic Brake Control Module.
  9. Test for less than 2 Ω in each chassis high speed GMLAN serial data circuit end to end between the non communicating device and the K17 Electronic Brake Control Module.
    • If 2 Ω or greater 

      Repair the open/high resistance in the serial data circuit.

    • Go to next step: If less than 2 Ω 
  10. Replace the non communicating device.
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