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Auxiliary Blower Motor Malfunction




Auxiliary Blower Motor Malfunction

Diagnostic Instructions

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

Diagnostic Fault Information






Circuit/System Description

The auxiliary blower motor control module is an interface between the HVAC control module and the auxiliary blower motor. The auxiliary blower motor speed control, battery positive and ground circuits enable the control module to operate. The HVAC control module provides a variable voltage to the auxiliary blower motor control module to request the selected auxiliary blower speed. The auxiliary blower motor control module provides a pulse width modulation (PWM) signal to the auxiliary blower motor in order to control the blower motor speed. The module supplies 12 volts to the blower motor through the auxiliary blower motor B+ circuit.

Reference Information
Schematic Reference

HVAC Schematics HVAC - Automatic
Connector End View Reference

Component Connector End Views Connector End Views By Name
Description and Operation

* Air Delivery Description and Operation Air Delivery
* Air Temperature Description and Operation Air Temperature

Electrical Information Reference

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

Scan Tool Reference

Control Module References Programming and Relearningfor scan tool information

Circuit/System Verification

Ignition ON, command the auxiliary blower motor ON and OFF with a scan tool. Observe that the auxiliary blower motor turns ON and OFF with each command.

Circuit/System Testing

1. Ignition OFF, disconnect the X2 harness connector at the auxiliary blower motor control module.
2. Test for less than 1.0 ohm between the ground circuit terminal 5 and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 6 and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse (REAR HVAC 30-amp) in the underhood fuse block is open, test all components connected to the B+ circuit and replace as necessary.

4. Connect a DMM between the control circuit terminal 3 and ground.
5. Cycle the auxiliary blower motor from OFF to HIGH. The voltage should increase while changing between the commanded states.

• If voltage remains greater than 11.5 volts while changing between the commanded states, test the control circuit for a short to voltage. If the circuit test normal, replace the HVAC control module.
• If voltage remains less than 1.0 volts while changing between the commanded states, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
• If voltage is between 1.0-11.5 volts and does not increase when changing between the commanded states, replace the HVAC control module.

6. Ignition OFF, connect the X2 harness connector at the auxiliary blower motor control module. Disconnect the harness connector at the auxiliary blower motor.
7. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal A and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the auxiliary blower motor control module.

8. Connect a test lamp between the control circuit terminal B and the B+ circuit terminal A.
9. Turn the auxiliary blower motor on high speed then to low speed. The test lamp intensity should be bright when in high speed and very dim or off when the blower is on low speed.

• If the test lamp intensity does not vary, test the control circuit for a short to voltage, short to ground, or an open/high resistance. If the circuit tests normal, replace the auxiliary blower motor control module.

10. If all circuits test normal, test or replace the auxiliary blower motor.

Component Testing

Install a 30A fused jumper wire between the auxiliary blower motor supply voltage terminal A and B+. Momentarily install a jumper wire between the auxiliary blower motor low reference terminal B and ground. The auxiliary blower motor should turn on.

If the function does not perform as specified, replace the auxiliary blower motor.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Auxiliary Blower Control Module Replacement Auxiliary Blower Control Module Replacement
* Auxiliary Blower Motor Replacement
* Control Module References Programming and Relearningfor HVAC control module replacement, setup, and programming

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