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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 Controller

The blower control module 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 module to operate. The HVAC control module provides a pulse width modulation (PWM) signal to the blower controller in order to command the blower motor speed. 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 knob dial in a desired speed position or by selecting automatic operation. In manual operation, the blower has 6 speed selections. The HVAC control module may alter the blower motor speed due to compensating factors. In automatic operation, the HVAC control module will determine what blower speed is necessary in order to achieve or maintain a desired temperature. In manual and automatic operation, the blower speed temporarily reduces speed during transition between outlet modes.


Reference Information
Schematic Reference

HVAC Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Automatic HVAC Description and Operation (HVAC - Automatic)
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, switch the Climate Control System to the manual setting. Press the fan speed control button from the lowest to highest setting. The blower motor speed should change between commanded states.
2. Press the power button located on the driver's side of the climate control panel to turn the entire climate control system ON or OFF. The blower motor should turn OFF.



Circuit/System Testing

1. Ignition OFF, disconnect the BLOWER relay.
2. Ignition ON, verify that a test lamp does not illuminate between the B+ circuit terminal R32 and ground.

• If the test lamp illuminates, test the B+ circuit for a short to voltage.

3. Verify that a test lamp illuminates between the B+ circuit terminal R30 and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

4. Verify that a test lamp illuminates between the B+ circuit terminal R29 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 BLOWER fuse is open, test the B+ circuit for a short to ground. If the circuit tests normal, replace the blower controller.

5. Connect a test lamp between the control circuit 754 and the B+.
6. Command the blower motor ON and OFF. The test lamp should turn ON and OFF when changing between the commanded states.

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

7. Connect the BLOWER relay.
8. Disconnect the harness connector at the blower controller.
9. Test for less than 1 ohm between the ground circuit terminal 5 and ground.

• If not the specified range, test the ground circuit for an open/high resistance.

10. Connect a test lamp between the B+ circuit terminal 6 and ground.
11. Turn ON the blower motor. Verify the test lamp illuminates

• If the test lamp does not illuminate, test the B+ circuit for an open/high resistance. If the circuit tests normal, test or replace the BLOWER relay.

12. Install a test lamp between the control circuit terminal 3 and B+.
13. Turn the blower motor ON and cycle between low and high speeds. The test lamp should dimly illuminate at high speeds and reduce in intensity as the blower speed is reduced.

• If the test lamp does not illuminate, test the control circuit for short to voltage or an open/high resistance. If the circuits test normal, test or 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, test or replace the HVAC control module.

14. Connect the harness connector at the blower controller.
15. Disconnect the harness connector at the blower motor.
16. Install at test lamp between the B+ circuit terminal 1 and ground.
17. Turn ON the blower motor. Verify the test lamp illuminates.

• If the test lamp does not illuminate, test the B+ circuit for an open/high resistance.

18. Install a test lamp between the control circuit terminal 1 and the low reference circuit terminal 2.
19. 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 does not illuminate, test the low reference circuit for short to voltage or an open/high resistance. If the circuit tests normal, test or replace the blower controller.
• If the test lamp does not change intensity, test the low reference circuit for a short to ground. If the circuit tests normal, test or replace the blower controller.

20. If all circuits test normal, replace the blower motor.



Component Testing


Blower Motor
1. Ignition OFF, disconnect the harness at the blower motor.
2. Install a 40-amp fused jumper wire between circuit terminal 1 and 12 volts. Install a jumper wire between the low reference circuit terminal 2 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 Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for blower controller and HVAC control module replacement, setup, and programming


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