Auxiliary Blower Motor Malfunction
Auxiliary Blower Motor MalfunctionDiagnostic Instructions
^ Perform the [Diagnostic System Check - Vehicle Diagnostic Information] prior to using this diagnostic procedure. Diagnostic System Check - Vehicle Diagnostic Information
^ Review [Strategy Based Diagnosis] for an overview of the diagnostic approach. Strategy Based Diagnosis
^ [Diagnostic Procedure Instructions - Vehicle Diagnostic Information] provides an overview of each diagnostic category. Diagnostic Procedure Instructions - Vehicle Diagnostic Information
Diagnostic Fault Information
Circuit/System Description
Auxiliary HVAC Control Module
The front HVAC control module must be in the ON position for GMLAN communication to allow the rear HVAC control module to operate.
Auxiliary Blower Motor Control Module
The following are auxiliary lower motor control module circuits:
^ Rear lower motor speed control circuit - When the auxiliary lower switch placed in any speed position this circuit a pulse width modulated signal that sent from the Auxiliary HVAC control module to the auxiliary lower motor control module.
^ Ground - A constant body ground supplied to the auxiliary lower motor control module.
^ Low reference - This circuit grounded through the auxiliary lower motor control module only when the auxiliary HVAC control module in high speed. In all other lower speeds this circuit a pulse width modulated signal (PWM). The longer this circuit pulsed the ground the faster the lower speed will be.
^ Blower speed feed back signal - This feedback circuit displays in percent on the TECH 2 the commanded output lower speed that the auxiliary lower motor control module sending to the auxiliary lower motor.
Auxiliary Blower Motor
The following are auxiliary lower motor circuits:
^ Ground - A constant body ground supplied the lower motor.
^ Ignition voltage - Ignition voltage supplied to the lower motor from the underhood fuse box.
^ Low reference - This circuit grounded through the auxiliary lower motor control module only when the auxiliary HVAC control module in high speed. In all other lower speeds this circuit a pulse width modulated signal (PWM). The longer this circuit pulsed the ground the faster the lower speed will be.
Circuit/System Testing
1. Ignition OFF, disconnect the auxiliary lower motor Connector X1 terminal 1.
2. Test for less than 1.0 ohm between the low reference circuit terminal 1 and ground.
^ If greater than 1.0 ohm, test the ground circuit for an open/high resistance.
3. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 2 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 open, replace the aux lower motor.
4. Ignition OFF, disconnect the harness connector at the auxiliary lower motor control module.
5. Ignition ON, verify that a test lamp does not illuminates between the control circuit terminal X2 pin 3 and ground.
^ If test lamp illuminates, test the control circuit for a short to voltage.
6. Test for less than 1.0 ohm between the ground circuit terminal X2 pin 5 and ground.
^ If greater than 1.0 ohm, test the ground circuit for an open/high resistance.
7. Connect the auxiliary lower motor connector.
8. Ignition ON, verity that a test lamp illuminates between the control circuit terminal X2 pin 3 and ground.
^ If test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance. If circuit test normal replace auxiliary lower motor.
9. Select the AUTO position on the front HVAC module.
10. Test for 12-27 mV between the control circuit terminal X2 pin3 and ground while adjusting the rear auxiliary HVAC control module lower from min to max.
^ If less than 12 mV, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal replace the rear auxiliary HVAC module.
^ If greater than 27 mV, test the control circuit for a short to voltage. If the circuit tests normal replace the rear auxiliary HVAC module.
11. Test for above 10 volts while adjusting the rear auxiliary HVAC lower switch to max setting.
^ If less than 10 volts replace the rear auxiliary HVAC control module.
12. Select the AUTO position on the rear auxiliary HVAC control module if equipped or press the AUX button on the front HVAC control to have the rear lower controls mimic the front control.
13. Test for 12-145 mV between the control circuit terminal X2 pin 3 and ground while adjusting the front HVAC control module lower from low speed to high speed.
^ If less than 12 mV, replace the front HVAC control module.
^ If greater than 145 mV, replace the front HVAC control module.
14. Place the front and rear HVAC modules in low speed.
15. Test for 0.2-15 mV between the signal circuit terminal X2 pin 3 and ground.
^ If less than 0.2 mV, test the signal circuit for a short to ground or an open high resistance. If the circuit tests normal replace the rear auxiliary HVAC module.
^ If greater than 15 mV, test the signal circuit for a short to voltage. If the circuit tests normal replace the rear auxiliary HVAC module.
16. If all circuits test normal, replace the auxiliary lower motor control module.
Repair Instructions
Perform the [Diagnostic Repair Verification - Vehicle Diagnostic Information] after completing the diagnostic procedure. Diagnostic Repair Verification - Vehicle Diagnostic Information
^ [Auxiliary Blower Motor Replacement]
^ [Auxiliary Blower Control Module Replacement]