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Blower Motor Malfunction



Blower Motor Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* 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/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 or low reference as a low side control to adjust the blower motor speed.

Air Speed

The blower motor forces air to circulate within the vehicles interior. The vehicle operator determines the blower motors speed by placing the blower motor switch in a desired speed position. The blower motor will only operate if the blower motor switch is in any position other than OFF, and the ignition switch is in the RUN position. Once a blower speed is selected, the blower speed remains constant until a new speed is selected.

As the requested blower speed increases, the following conditions occur:

* The HVAC control module increases the amount of time that the blower motor speed control circuit is modulated to ground.
* The voltage and duty cycle, measured between the blower motor speed control circuit and ground, decrease.

As the requested blower speed decreases, the following conditions occur:

* The HVAC control module decreases the amount of time that the blower motor speed control circuit is modulated to ground.
* The voltage and duty cycle, measured between the blower motor speed control circuit and ground, increase.

Diagnostic Aids

Be sure the blower motor housing is not shorted to a grounded surface causing the blower motor to always be on in high speed.

Circuit/System Verification

1. Ignition ON, command the blower motor from Off to Low through High by changing the blower motor switch from Off through to the High speed positions, the blower motor should turn ON and operate from Low to High when changing between the commanded states.
2. Observe the scan tool Blower Motor Speed Command parameter while changing the blower motor switch from Off through to the High speed positions. The display should change from 0% to 100%.

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

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector X2 at the blower motor control processor.
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 is open, replace the blower motor control processor.

4. Connect a test lamp between the blower motor speed control circuit terminal 3 and ground.
5. Command 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 ground circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.
^ If the test lamp does not change intensity, test the control circuit for a short to ground. If the circuit tests normal, replace the HVAC control module.

6. Ignition OFF, connect the harness connector X2 at the blower motor control processor and disconnect the harness connector at the blower motor.
7. Ignition ON, verify that a test lamp illuminates between the signal circuit terminal 2 and ground.

^ If the test lamp does not illuminate, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the blower motor control processor.

8. Connect a test lamp between the ground circuit terminal 1 and B+.
9. Command 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 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 does not change intensity, test the control circuit for a short to ground. If the circuit tests normal, replace the blower motor control processor.

10. 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 signal circuit terminal 2 and 12 volts. Install a jumper wire between the ground circuit terminal 1 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 after completing the diagnostic procedure. Verification Tests

* Blower Motor Control Module Replacement
* Blower Case Assembly Replacement.
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