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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1138 (HVAC System - Automatic) >> Diagnostic Information and Procedures >> DTC B0248, B0268, B0408, B0413, B0418, B0423, B3761, or B3773 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2008 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, test for less than 1 ohm of resistance between the low reference circuit and ground.
    • If greater than 1 ohm, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
  2. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit and ground.
    • If less than 4.8 volts, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
    • If greater than 5.2 volts, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.
  3. Verify the appropriate scan tool parameter is less than 4 counts.
    • If greater than 4 counts, test the signal circuit terminal 3 for a short to ground. If the circuit tests normal, replace the HVAC control module.
  4. Install a 3-amp fused jumper wire between the signal circuit terminal 3 and the low reference circuit terminal. Verify the appropriate scan tool parameter is greater than 250 counts.
    • If less than 250 counts, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
  5. Ignition ON, after 30 seconds verify that a test lamp illuminates between control circuit A terminal and B+.
    • If the test lamp does not illuminate, test the control circuit for a short to voltage or an open/high resistance. If circuit tests normal replace the HVAC control module.
  6. Ignition OFF, verify that the test lamp does not illuminate between control circuit A terminal and B+.
    • If the test lamp illuminate, test the control circuit for a short to ground. If circuit tests normal replace the HVAC control module.
  7. Ignition ON, after 30 seconds verify that a test lamp illuminates between control circuit B terminal and B+.
    • If the test lamp does not illuminate, test the control circuit for a short to voltage or an open/high resistance. If circuit tests normal replace the HVAC control module.
  8. Ignition OFF, verify that the test lamp does not illuminate between control circuit B terminal and B+.
    • If the test lamp illuminate, test the control circuit for a short to ground. If circuit tests normal replace the HVAC control module.
  9. If all circuits test normal, replace the actuator.
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