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HOMESERVICE MANUALSCHEVROLET2025TAHOE COMMERCIAL, 4WDREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMDATA COMMUNICATIONS - DIAGNOSTIC INFORMATION AND PROCEDURES (1 OF 4)DIAGNOSTIC INFORMATION AND PROCEDURESDTC B1A1B (K56 SERIAL DATA GATEWAY MODULE)CIRCUIT/SYSTEM TESTING
2025 Chevrolet Tahoe Commercial, 4WD

Circuit/System Testing

2025 Chevrolet Tahoe Commercial, 4WDSECTION Circuit/System Testing
NOTE:

Use the schematics and connector end views to identify the control module's ground, B+, ignition, and Ethernet serial data circuit terminals.

  1. Ignition/Vehicle OFF, disconnect the harness connectors at the A11 Radio.
  2. Verify a test lamp illuminates between each of the ground circuit terminals and B+.
    • If the test lamp does not illuminate 

      Repair the open/high resistance in the ground circuit or ground connection.

    • Go to next step: If the test lamp illuminates 
  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. Test for an open/high resistance in the B+ circuit.
      • If an open/high resistance is found, repair the fault on the circuit.
      • Go to next step: If an open/high resistance is not found
    2. 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. Test for a short to ground in the B+ circuit.
      • If a short to ground is found, repair the fault in the circuit.
      • Go to next step: If a short to ground is not found
    2. Replace the A11 Radio.
    • 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. Test for an open/high resistance in the ignition circuit.
      • If an open/high resistance is found, repair the fault in the circuit.
      • Go to next step: If an open/high resistance is not found
    2. 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. Test for a short to ground in the ignition circuit.
      • If a short to ground is found, repair the fault in the circuit.
      • Go to next step: If a short to ground is not found
    2. Replace the A11 Radio.
    • Go to next step: If the test lamp illuminates 
  6. Ignition/Vehicle OFF, disconnect the harness connectors at the K56 Serial Data Gateway Module.
  7. Ignition ON/Vehicle In Service Mode.
  8. Test for less than 4.5 V between each of the Ethernet bus 2 circuit terminals and ground.
    • If 4.5 V or greater 

      Repair the short to voltage in the circuit.

    • Go to next step: If less than 4.5 V 
  9. 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.
  10. Test for infinite resistance between each of the Ethernet bus 2 circuit terminals and ground.
    • If less than infinite resistance 

      Repair the short to ground in the circuit.

    • Go to next step: If infinite resistance 
  11. Test for infinite resistance between the pair of the Ethernet bus 2 circuit terminals.
    • If less than infinite resistance 

      Repair the short together in the circuits.

    • Go to next step: If infinite resistance 
  12. Test for less than 2 Ω in each of the Ethernet bus 2 circuits end to end.
    • If 2 Ω or greater 

      Repair the open/high resistance in the circuit.

    • Go to next step: If less than 2 Ω 
  13. Replace the A11 Radio.
  14. 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.
  15. Ignition ON/Vehicle In Service Mode.
  16. Verify DTC B1A1B does not set.
    • If the DTC sets 

      Replace the K56 Serial Data Gateway Module.

    • Go to next step: If the DTC does not set 
  17. All OK.
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.