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Blower Motor Malfunction




Blower Motor Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.

Diagnostic Fault Information





Circuit/System Description

Blower Motor Control Processor

The blower motor control processor is an interface between the HVAC control module and the blower motor. The blower motor speed control, battery positive and ground circuits enable the control processor to operate. The HVAC control module provides a pulse width modulation (PWM) signal to the blower motor speed control processor in order to command the blower motor speed. The processor supplies 12 volts to the blower motor through the blower motor voltage supply circuit. The control processor uses the blower motor ground as a low side control to adjust the blower motor speed.

Diagnostic Aids

Be sure the blower motor housing is not shorted to a grounded surface causing the blower motor to run continuously at high speed.

Reference Information
Schematic Reference

HVAC Schematics (HVAC - Manual)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

* Air Temperature Description and Operation (Air Temperature Description and Operation)
* Air Delivery Description and Operation (Air Delivery Description and Operation)

Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

1. Ignition ON, command the blower motor ON and OFF with a scan tool. The blower motor should turn ON and OFF when changing between the commanded states.
2. Observe the scan tool Commanded Blower parameter while changing the blower motor switch from Off through to the High speed positions. The display should change from 0-100 percent.

• If the display does not change, replace the HVAC control module.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the blower motor control processor.
2. Test for less than 1.0 ohm of resistance between the ground circuit terminal A 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 C 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 is open, replace the blower motor control processor.

4. Ignition OFF, connect the harness connector at the blower motor control processor and disconnect the harness connector at the blower motor.
5. Connect a test lamp between the control circuit terminal B and B+.
6. Ignition ON, command the blower motor ON and OFF with a scan tool, the test lamp should turn ON and OFF when changing between the commanded states.

• If the test lamp is always OFF, test the ground circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the blower motor control processor.
• If the test lamp is always ON, test the ground circuit for a short to ground. If the circuit tests normal, replace the blower motor control processor.

7. Connect a test lamp between the control circuit terminal A and ground.
8. Turn the blower motor ON and cycle between low and high speeds. The test lamp should illuminate and change in intensity as the blower speed is varied.

• If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the blower motor control processor.
• If the test lamp does not change intensity, test the control circuit for a short to voltage. If the circuit tests normal, replace the blower motor control processor.

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

Component Testing

1. Ignition OFF, disconnect the harness connector at the blower motor.
2. Install a 30-amp fused jumper wire between the control circuit terminal A and 12 volts. Install a jumper wire between the control circuit terminal B and ground. Verify the blower motor activates.

• If the blower motor does not activate, replace the blower motor.

Repair Instructions

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

* Blower Motor Control Module Replacement (Blower Motor Control Module Replacement)
* Blower Motor Replacement (Service and Repair)
* Control Module References (Programming and Relearning) HVAC control module replacement, setup, and programming

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