The auxiliary blower motor is controlled by the front auxiliary blower motor switch. If the vehicle is equipped with a rear digital video disc player (DVD player) (RPO U32), the auxiliary blower motor can be controlled by the overhead console, vehicle entertainment system (VES). The front auxiliary blower switch must be in the AUX position in order to control blower speed from the VES. The VES will send a class 2 message to the HVAC control module requesting a blower motor speed.

The auxiliary blower motor control module is an interface between the HVAC control module and the auxiliary blower motor. The auxiliary blower motor speed control, auxiliary blower motor speed signal, blower motor speed control, and ground circuits enable the control processor to operate. The HVAC control module sends the commanded blower motor speed to the control processor through a 0 to 8-volt linear ramped blower motor speed control circuit. As the blower motor speed control voltage increases, the blower motor speed increases. The control processor sends the actual blower speed to the HVAC control module through a 0 to 12-volt blower motor speed signal circuit. The control processor uses the blower motor ground as a low side control to adjust the blower motor speed. The underhood fuse block supplies 12 volts to the blower motor through the blower motor voltage supply circuit.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for Scan Tool Information

1. Ignition ON, command the auxiliary blower motor ON and OFF with a scan tool, the auxiliary blower motor should turn ON and OFF when changing between the commanded states.

⇒	If the auxiliary blower motor is always OFF, refer to Blower Motor Inoperative.

2. Place the auxiliary blower switch in the 1, 2 and 3 position. The auxiliary blower motor speed should vary in each speed position.

⇒	If the auxiliary blower motor speed does not vary, refer to Blower Motor Malfunction.

3. Place the auxiliary blower switch on the HVAC control module in the Aux position and command the auxiliary blower motor using the aux fan speed select switch on the DVD player. The auxiliary blower motor speed should vary in each speed position.

⇒	If the auxiliary blower motor speed does not vary, refer to Aux Fan Speed Switch Malfunction.

Blower Motor Inoperative

1. Ignition OFF, disconnect the harness connector at the auxiliary blower motor control module.
2. Ignition OFF, 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. Ignition OFF, connect the harness connector at the auxiliary blower motor control module and disconnect the harness connector at the auxiliary blower motor.
4. Connect a test lamp between the B+ circuit terminal A and the control circuit terminal B.
5. Command the auxiliary blower motor to operate from HIGH to OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the auxiliary blower motor control module.

⇒	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 auxiliary blower motor control module.

6. If all circuits test normal, test or replace the auxiliary high speed blower.

Blower Motor Malfunction

1. Ignition ON, observe the scan tool Aux Blower Motor Switch parameter while placing the auxiliary blower motor switch on the HVAC control module in the Aux, 0, 1, 2 and 3 positions. The reading should change from Auxiliary, Off, 1, 2 and 3.

⇒	If the parameter does not change or reads Invalid, replace the HVAC control module.

2. Ignition OFF, disconnect the harness connector at the auxiliary blower motor.
3. Connect a test lamp between the B+ circuit terminal A and the control circuit terminal B.
4. Ignition ON, cycle the auxiliary blower motor switch between 1, 2 and 3. 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 voltage or an open/high resistance. If the circuit tests normal, replace the auxiliary blower motor 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 auxiliary blower motor control module.

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

Aux Fan Speed Switch Malfunction

Ignition ON, place the auxiliary blower switch on the HVAC control module in the Aux position, observe the scan tool Aux Blower Motor Switch parameter while using the auxiliary blower motor switch on the DVD player. The reading should change from 1, 2 and 3.

1. Ignition OFF, disconnect the harness connector at the auxiliary blower motor.
2. Install a 30-amp fused jumper wire between the B+ terminal A and 12 volts. Install a jumper wire between the control circuit terminal B and ground. Verify the auxiliary blower motor activates.

⇒	If the auxiliary blower motor does not activate, replace the auxiliary blower motor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.