Auxiliary Blower Motor Malfunction

Auxiliary 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.



Circuit/System Description

The HVAC control assembly applies a ground to the blower motor control circuit that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request:

* Low speed, 3 resistors
* Medium 1 speed, 2 resistors
* Medium 2 speed, 1 resistors


When the operator requests High speed, the HVAC control assembly applies ground to the high speed blower relay control circuit. When the relay contacts close, ground is applied directly to the blower motor through the blower motor resistor.


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 (Automatic HVAC Description and Operation (Part 1))
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, place the blower switch in the highest speed position, the blower motor should operate at High speed.

• If the blower motor does not function properly in the High speed position, perform the High Speed Blower Malfunction test.

2. Place the blower switch in Low, Medium 1 and Medium 2 speed positions. The blower motor should operate in each speed position.

• If the blower motor speed does not correspond with the selected switch position, perform the Blower Malfunction Test.




Circuit/System Testing


High Speed Blower Malfunction
1. Ignition OFF, disconnect the harness connector at the HVAC control module.
2. Test for less than 1.0 ohm of resistance between the ground circuit terminal 4 and ground.

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

3. Connect the harness connector at the HVAC control module.
4. Disconnect the high speed blower relay.
5. Place the blower switch in the high speed position.
6. Test for less than 1.0 ohm of resistance between the ground circuit terminal 5 and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance. If the circuit test normal test or replace the HVAC control module.

7. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 2 and ground.

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

8. Test for less than 1.0 ohm of resistance between the ground circuit terminal 1 and ground.

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

9. Connect the high speed blower relay. Disconnect the harness connector at the blower motor resistor.
10. Ignition ON, place the blower switch in the high speed position.
11. Test for less than 1.0 ohm of resistance between the control circuit terminal E at the blower motor resistor and ground.

• If greater than the specified range, test the control circuit for an open/high resistance. If the circuit test normal test or replace the high speed blower relay.

12. Ignition OFF, connect the harness connector at the blower motor resistor. Connect the high speed blower relay. Disconnect the harness connector at the blower motor.
13. Ignition ON, place the blower switch in the high speed position.
14. Verify that a test lamp illuminates between the control circuit terminal 1 and B+.

• If the test lamp does not illuminate, test the control circuit for an open/high resistance.
• If the circuit test normal, test or replace the blower motor resistor.

15. Verify that a test lamp illuminates between the ignition circuit terminal 2 and ground.

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

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



Blower Malfunction
1. Ignition OFF, disconnect the harness connector at the HVAC control module.
2. Test for less than 1.0 ohm of resistance between the ground circuit terminal 5 and ground.

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

3. Connect the harness connector at the HVAC control module.
4. Disconnect the harness connector at the blower motor resistor.
5. Ignition ON, place the blower switch in the appropriate speed for the circuit being tested.
6. Verify that a test lamp illuminates between the appropriate control circuit and B+.

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

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



Repair Instructions

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

* Auxiliary Blower Motor Replacement (Service and Repair)
* Auxiliary Blower Motor Switch Replacement (C57) (Service and Repair)
* Auxiliary Blower Motor Resistor Replacement (Service and Repair)
* Control Module References (Programming and Relearning)for HVAC control module replacement, setup, and programming