Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Blower Motor Control Processor B+ | 1 | 1 | -- | -- |
Blower Motor Speed Control | 1 | 1 | 2 | -- |
Blower Motor Control Processor Ground | -- | 1 | 1 | -- |
1. Blower Motor Inoperative 2. Blower Motor Always On | ||||
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.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Automatic HVAC Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
- 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.
- 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
- Ignition OFF, disconnect the harness connector at the blower motor control processor.
- Test for less than 1.0 ohm between the ground circuit terminal C and ground.
- Ignition ON, verify that a test lamp illuminates between B+ and the circuit terminal A and ground.
- Connect a DMM between B+ and the control circuit terminal B.
- Cycle the blower motor from OFF to HIGH. The voltage should increase while changing between the commanded states.
- If all circuits test normal, replace the blower motor control processor.
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | 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. |
| ⇒ | If voltage remains greater than 11.5 volts while changing between the commanded states, test the control circuit for a short to ground. If the circuit test normal, replace the HVAC control module. |
| ⇒ | If voltage remains less than 1.0 volts while changing between the commanded states, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module. |
| ⇒ | If voltage is between 1.0-11.5 volts and does not increase when changing between the commanded states, replace the HVAC control module. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for HVAC control module replacement, setup, and programming |
