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Home >> Cadillac >> 2021 >> XT5 Sport >> Repair and Diagnosis >> External Pages >> Different car >> Section 734 (Keyless Entry System And Remote Functions) >> Diagnostic Information and Procedures >> DTC B3121 >> Circuit/System Testing
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Circuit/System Testing

WARNING: This page is about a different car, the 2023 GMC Sierra 3500 HD and 2023 GMC Sierra 2500 HD. However, it is still accessible from the selected car via links, so may be relevant.
    NOTE:

    It may take up to 2 min for all vehicle systems to power down before an accurate ground or low reference circuit continuity test can be performed.

  1. Ignition/Vehicle & All vehicle systems - Off
  2. Disconnect the electrical connector: T10G Keyless Entry Antenna - Rear Fascia
  3. Test for less than 1 V between the test points: Terminal 1 & Ground
    • If 1 V or greater 
    1. Ignition/Vehicle & All vehicle systems - Off
    2. Disconnect the electrical connector: K84 Keyless Entry Control Module
    3. Ignition/Vehicle - On
    4. Test for less than 1 V between the test points: Signal circuit & Ground
      • If 1 V or greater - Repair the short to voltage on the circuit.
      • If less than 1 V - Replace the component: K84 Keyless Entry Control Module
    • Go to next step: If less than 1 V 
  4. Ignition/Vehicle & All vehicle systems - Off
  5. Connect a DMM between the test points: Terminal 1 & Ground
  6. Measure = Voltage - (min/max)
  7. Keyless Entry Transmitter - All Doors Lock
  8. Rear Closure - Open
    • If less than 1 V 
    1. Ignition/Vehicle & All vehicle systems - Off
    2. Disconnect the electrical connector: K84 Keyless Entry Control Module
    3. Test for infinite resistance between the test points: Signal circuit & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • Go to next step: If infinite resistance 
    4. Test for less than 2 ohms between the test points: Signal circuit@Component harness & The other end of the circuit
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Replace the component: K84 Keyless Entry Control Module
    • Go to next step: If greater than 1 V 
  9. Test for less than 1 V between the test points: Terminal 2 & Ground
    • If 1 V or greater 
    1. Ignition/Vehicle - Off
    2. Disconnect the electrical connector: K84 Keyless Entry Control Module
    3. Test for less than 1 V between the test points: Low Reference circuit & Ground
      • If 1 V or greater - Repair the short to voltage on the circuit.
      • If less than 1 V - Replace the component: K84 Keyless Entry Control Module
      • Go to next step: If less than 1 V 
  10. Ignition/Vehicle & All vehicle systems - Off
  11. Connect a DMM between the test points: Terminal 2 & Ground
  12. Measure = Voltage - (min/max)
  13. Keyless Entry Transmitter - All Doors Lock
  14. Rear Closure - Open
    • If less than 1 V 
    1. Ignition/Vehicle & All vehicle systems - Off
    2. Disconnect the electrical connector: K84 Keyless Entry Control Module
    3. Test for infinite resistance between the test points: Low Reference circuit & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • Go to next step: If infinite resistance 
    4. Test for less than 2 ohms between the test points: Signal circuit@Component harness & The other end of the circuit
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Replace the component: K84 Keyless Entry Control Module
    • Go to next step: If greater than 1 V 
  15. Replace the component: T10G Keyless Entry Antenna - Rear Fascia
  16. Keyless Entry Transmitter - All Doors Lock
  17. Rear Closure - Open
  18. Verify DTC B3121 is not set.
    • If DTC B3121 is set 

      Replace the component: K84 Keyless Entry Control Module

    • Go to next step: If DTC B3121 is not set 
  19. All OK.
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