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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2009 🢒 Express - AWD 🢒 HVAC 🢒 HVAC - Manual 🢒 Air Delivery Improper - Auxiliary

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Front Auxiliary HVAC Control Assembly B+

1

1

--

--

Rear Auxiliary HVAC Control Assembly B+

2

2

--

--

Auxiliary Mode Actuator Ignition

1, 2

1, 2

--

--

Front Auxiliary Mode Signal

1

1

1

--

Rear Auxiliary Mode Signal

2

2

2

--

Auxiliary Mode Actuator Control

1, 2

1, 2

1, 2

--

Auxiliary Mode Actuator Ground

--

1, 2

--

--

1. Auxiliary Mode Selection Inoperative from Front Control

2. Auxiliary Mode Selection Inoperative from Rear Control

Circuit/System Description

The auxiliary mode actuator is a 3-wire bi-directional electric motor. Ignition 3 voltage, ground and control circuits enable the actuator to operate. The control circuit uses a 0-12 volts linear-ramped signal to command the actuator movement. The 0 and 12-volt control values represent the opposite limits of the actuator range of motion. The values in between 0 and 12 volts correspond to the positions between the limits.

When the HVAC control assembly sets a commanded, or targeted, value, the control signal is set to a value between 0-12 volts. The actuator shaft rotates until the commanded position is reached. The module will maintain the control value until a new commanded value is needed.

Diagnostic Aids

Inspect the auxiliary mode door and the auxiliary mode actuator for the following conditions:

    • A misaligned auxiliary mode actuator.
    • Broken or binding linkages or auxiliary mode door.
    • An obstruction that prevents the auxiliary mode door from operating within its full range of motion.
    • Missing seals to the auxiliary mode door.
    • Misaligned seals to the auxiliary mode door.

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

    •  Air Temperature Description and Operation
    •  Air Delivery Description and Operation

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Circuit/System Verification

With Rear Auxiliary Controls

  1. Ignition ON, cycle the front auxiliary HVAC control assembly blower switch through the LOW, MED, and HIGH speeds. The blower motor should operate at all speeds.
    2. ⇒If the blower motor is inoperative, refer to Auxiliary Blower Motor Malfunction .
  2. Rotate the front auxiliary HVAC control assembly air temperature control from the VENT position to the FLOOR position. The mode should follow the commanded states VENT to FLOOR.
    3. ⇒If the mode does not change, refer to Mode Malfunction - Front Auxiliary Control.
  3. Front auxiliary HVAC control assembly blower switch in the AUX position, cycle the rear auxiliary HVAC control assembly blower switch through the LOW, MED, and HIGH speeds. The blower motor should operate at all speeds.
    4. ⇒If the blower motor is inoperative, refer to Auxiliary Blower Motor Malfunction .
  4. Rotate the rear auxiliary HVAC control assembly air temperature control from the VENT position to the FLOOR position. The mode should follow the commanded states VENT to FLOOR.
    5. ⇒If the mode does not change, refer to Mode Malfunction - Rear Auxiliary Control.

Without Rear Auxiliary Controls

  1. Ignition ON, cycle the front auxiliary HVAC control assembly blower switch through the LOW, MED, and HIGH speeds. The blower motor should operate at all speeds.
    2. ⇒If the blower motor is inoperative, refer to Auxiliary Blower Motor Malfunction .
  2. Rotate the front auxiliary HVAC control assembly air temperature control from the VENT position to the FLOOR position. The mode should follow the commanded states VENT to FLOOR.
    3. ⇒If the air temperature does not change, refer to Mode Malfunction without Rear Auxiliary Control.

Circuit/System Testing

Mode Malfunction - Front Auxiliary Control

  1. Ignition OFF, disconnect the harness connector at the front auxiliary HVAC control assembly.
  2. Ignition ON, verify a test lamp illuminates between the ignition circuit terminal J and ground.
    3. ⇒If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  3. Ignition OFF, connect the harness connector at the front auxiliary HVAC control assembly. Disconnect the harness connector at the auxiliary HVAC control assembly.
  4. Ignition ON, test for ignition voltage between the signal circuit terminal E and ground.
    5. ⇒If less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the front auxiliary HVAC control assembly.
  5. Ignition OFF, connect the harness connector at the auxiliary HVAC control assembly. Disconnect the harness connector at the auxiliary mode actuator.
  6. Test for less than 5 ohms between the ground circuit terminal 7 and ground.
    7. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  7. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 10 and ground.
    8. ⇒If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  8. Install a DMM between the control circuit terminal 8 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 12 volts in the other direction.
    9. ⇒If the voltage does not change as specified, replace the auxiliary HVAC control assembly.
  9. If all circuits test normal, test or replace the auxiliary mode actuator.

Mode Malfunction - Rear Auxiliary Control

  1. Ignition OFF, disconnect the harness connector at the rear auxiliary HVAC control assembly.
  2. Test for less than 5 ohms between the ground circuit terminal B and ground.
    3. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify a test lamp illuminates between the ignition circuit terminal G and ground.
    4. ⇒If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  4. Ignition OFF, connect the harness connector at the front auxiliary HVAC control assembly. Disconnect the harness connector at the auxiliary HVAC control assembly.
  5. Ignition ON, test for ignition voltage between the signal circuit terminal D and ground.
    6. ⇒If less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the rear auxiliary HVAC control assembly.
  6. If all circuits test normal, replace the auxiliary HVAC control assembly.

Mode Malfunction without Rear Auxiliary Control

  1. Ignition OFF, disconnect the harness connector at the front auxiliary HVAC control assembly.
  2. Ignition ON, verify a test lamp illuminates between the ignition circuit terminal G and ground.
    3. ⇒If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  3. Ignition OFF, connect the harness connector at the front auxiliary HVAC control assembly. Disconnect the harness connector at the auxiliary mode actuator.
  4. Test for less than 5 ohms between the ground circuit terminal 7 and ground.
    5. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  5. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 10 and ground.
    6. ⇒If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  6. Install a DMM between the control circuit terminal 8 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 12 volts in the other direction.
    7. ⇒If the voltage does not change as specified, replace the front auxiliary HVAC control assembly.
  7. If all circuits test normal, test or replace the auxiliary mode actuator.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Auxiliary Mode Valve Actuator Replacement
    •  Auxiliary Heater and Air Conditioning Control Replacement - Front
    •  Auxiliary Heater and Air Conditioning Control Replacement - Rear
    •  Auxiliary HVAC Control Processor Replacement