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.
Air Speed
The blower motor forces air to circulate within the vehicles interior. The vehicle operator determines the blower motor 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 ON 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.
Reference Information
Schematic Reference
HVAC Schematics (Electrical Diagrams)
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 Blower Motor Speed 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 C 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 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 and the B+ circuit fuse is open, replace the blower motor control processor.
4. Connect a test lamp between the control circuit terminal B and ground.
5. Command the blower motor ON and cycle between low and high speeds by using the fan speed control switch. 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 HVAC control module.
• If the test lamp does not change intensity, test the control circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.
6. If all circuits test normal, replace the blower motor control processor.
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 HVAC control module setup, replacement, and programming