Diagnostic Instructions
Circuit/System Description
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.
Reference Information
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
Circuit/System Verification
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.
Circuit/System Testing
- Ignition OFF, disconnect the harness connector X2 at the Auxiliary Blower Motor Control Module.
- Ignition OFF, test for less than 1.0 ohm of resistance between the ground circuit terminal 5 and ground.
⇒ | If greater than 1.0 ohm, test the ground circuit for an open/high resistance. |
- Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 6 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 REAR HVAC fuse is open, test battery positive voltage circuit for a short to ground. |
- Test for the following voltages between the control circuit terminal 3 and ground with the auxiliary blower motor speed set at the specified levels:
• | Level 3--0.5-10.5 volts |
• | Level 4--0.5-11.5 volts |
⇒ | If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the HVAC Control Module. |
⇒ | If less than the specified range, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC Control Module. |
- Reconnect the harness connect X2 at the Auxiliary Blower Motor Control Module. Disconnect the harness connector at the auxiliary blower motor.
- 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, replace the Auxiliary Blower Motor Control Module. |
- Install a test lamp between the B+ circuit terminal A and the low reference circuit terminal B.
- While monitoring the test lamp, cycle the auxiliary blower motor through the various speeds. The test lamp should not illuminate with the auxiliary blower motor in the OFF position and become progressively brighter as the auxiliary blower motor speed
is increased.
⇒ | If the test lamp is ON with the auxiliary blower motor in the OFF position, test the low reference circuit terminal B 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 low reference circuit terminal B 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 become progressively brighter as the auxiliary blower motor speed is increased, replace the Auxiliary Blower Motor Control Module. |
- If all circuits test normal, test or replace the auxiliary blower motor.
Component Testing
Install a 30A fused Jumper wire between the auxiliary blower motor supply voltage terminal A and B+. Momentarily install a jumper wire between the auxiliary blower motor low reference terminal B and ground. The auxiliary blower motor should
turn on.
⇒ | If the function does not perform as specified, replace the auxiliary blower motor. |
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.