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Home >> Hummer >> 2008 >> H2 4D Utility Wagon >> Repair and Diagnosis >> External Pages >> Different car >> Section 127 (HVAC System - Automatic) >> Diagnostic Information and Procedures >> DTC B0228, B0413, B0423, B0433, B3779 or B3782 >> Circuit/System Testing

Circuit/System Testing

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  1. Ignition OFF, disconnect the appropriate actuator and 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 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 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 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, verify that a test lamp illuminates between the ignition 3 circuit and ground.
    • If the test lamp does not illuminate, test the ignition 3 circuit for a short to ground an open/high resistance.
  6. Install a DMM between the actuator control circuit and ground. While monitoring the DMM use the scan tool to command the appropriate actuator from one direction to the other. If the voltage on the control circuit moves from 0 volts in one direction to 5 volts in the other direction and 2.5 volts in the at rest state.
    • If the voltage does not change, test the control circuit for an open, short to voltage or short to ground. If circuit tests normal replace the HVAC control module.
  7. If all circuits test normal, replace the actuator.
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