The auxiliary blower motor is a variable speed fan. The HVAC control module controls the fan speed by sending a pulse width modulated signal to the auxiliary blower motor control module. The auxiliary blower motor control module varies the voltage drop across the auxiliary blower motor in relation to the pulse width modulated signal. The auxiliary blower motor speed can be adjusted from 10 percent to 90 percent duty cycle (PWM), 90 percent is considered high speed fan. During normal operation the control circuit voltage will be low and near battery voltage when OFF.

Schematic Reference

HVAC Schematics

Connector End View Reference

HVAC Connector End Views

Description and Operation

Air Delivery Description and Operation

Electrical Information Reference

Scan Tool Reference

Ignition ON, command the auxiliary blower motor ON and OFF with a scan tool. Observe that the auxiliary blower motor turns ON and OFF with each command.

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 and ground.

⇒	If greater than 1.0 ohm, test the ground circuit for an open/high resistance.

3. Ignition ON, test for B+ between the battery positive voltage circuit and ground.

⇒	If less than B+, test the battery positive voltage circuit for a short to ground or an open/high resistance. If the REAR HVAC fuse is open, test battery positive voltage circuit for a short to ground.

4. With a DMM, test for B+ between the B+ circuit terminal 6 and the control circuit terminal 3.

⇒	If less than B+, test the control circuit for and open/high resistance. If the circuit tests normal replace the HVAC control module.

5. Test for 1.5-0.5 ohms of resistance between the low reference terminal 2 and supply voltage terminal 1.

⇒	If not within specified value, test and replace the auxiliary blower motor.

6. If all circuits test normal, test and replace the auxiliary blower motor control module.

Install a 30A fused Jumper wire between the auxiliary blower motor supply voltage terminal 1 and B+. Momentarily install a jumper wire between the auxiliary blower motor low reference terminal 2 and ground. The auxiliary blower motor should turn on.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.