LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Chevrolet >> 2011 >> Caprice >> Repair and Diagnosis >> Engine Performance >> System >> Data Communications System >> Diagnostic Information and Procedures >> DTC U1304 >> Circuit/System Testing
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Circuit/System Testing

  1. Ignition OFF, disconnect the SIM harness connector.
  2. Test for less than 1 ohm between the module ground circuits and ground.
    • If greater than 1 ohm, repair the ground circuit for an open/high resistance.
  3. Ignition ON, verify that a test lamp illuminates between all battery positive voltage circuits and ground.
    • If the test lamp does not illuminate, repair the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the SIM.
  4. Verify that a test lamp illuminates between all ignition voltage circuits and ground.
    • If the test lamp does not illuminate, repair the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the SIM for a short to ground. If the circuits test normal, replace the SIM.
  5. Ignition ON, verify that a test lamp illuminates between the serial data communication enable circuit OR the accessory wakeup serial data circuit and ground.
    • If the test lamp does not illuminate, repair the circuit for an open/high resistance. If the circuits test normal, replace the BCM.
  6. Test for less than 1 ohm in the low speed GMLAN serial data circuit between the SIM and the module that displays the DTC.
    • If greater than 1 ohm, test the low speed GMLAN serial data circuit for open/high resistance.
  7. If all circuits test normal, replace the SIM.
scientia non olet · About LEMON Manuals