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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 866 (HVAC System - Automatic) >> Diagnostic Information and Procedures >> DTC B0228, B0413, B0423, or B3779 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the harness connector at the applicable actuator.
  2. Ignition OFF, test for less than 1 ohm of resistance between the low reference circuit terminal 7 and ground.
    • If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module.
  3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 10 and ground.
    • If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.
    • If less then specified range, 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.
  4. Verify the applicable scan tool parameter is less than 7 counts.
    • If greater than the specified range, test the signal circuit terminal 9 for a short to ground. If the circuit tests normal, replace the HVAC control module.
  5. Install a 3A fused jumper wire between the signal circuit terminal 9 and the low reference circuit terminal 7. Verify the applicable scan tool parameter is greater than 250 counts.
    • If less than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
  6. Verify that a test lamp illuminates between the ignition circuit terminal 5 and ground.
    • If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  7. Test for 2.5 volts between the control circuit terminal 6 and ground.
    • If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.
    • If less then specified range, 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.
  8. Install a DMM between the control circuit terminal 6 and ground. Command the actuator in each direction. Voltage on the control circuit should change from 0 volts when commanding the actuator in one direction to 5 volts in the other direction and return to 2.5 volts in the at rest state.
    • If the voltage does not change as specified, replace the HVAC control module.
  9. If all circuits test normal, test or replace the applicable actuator.
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