For 1990-2009 cars only
Diagnostic Fault Information
Perform the Diagnostic System Check - HVAC Systems - Manual prior to using this diagnostic procedure.
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Battery Positive Voltage Circuit | 1 | 1 | -- | -- |
Blower Motor Control Processor Ground | 2 | 1 | 1 | -- |
Blower Motor Speed Control Circuit | 1 | 1 | 1 | -- |
Blower Motor Supply Voltage Circuit | 1 | 1 | 1 | -- |
Blower Motor Ground Circuit | 2 | 1 | -- | -- |
1. Blower Motor Inoperative 2. Blower Motor Always On | ||||
Circuit/System Description
The blower motor control processor has three input and two outputs.
Blower motor control processor input signals:
| • | The BATT MAIN 4 fuse in the underhood fuse block supplies B+. |
| • | The HVAC control module supplies a pulse width modulated (PWM) signal input that varied depending on the blower motor speed selected . |
| • | Body ground. |
Blower motor control processor output signals:
| • | The blower motor supply voltage circuit outputs 12 volts to the blower motor when the blower motor is ON. |
| • | The blower motor ground circuit is pulsed on and off to control the speed of the blower. The ground circuit is pulsed to ground for a longer period of time as blower motor speed is increased. |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Air Delivery Description and Operation
Electrical Information Reference
Scan Tool Reference
Circuit/System Testing
- Ignition OFF, disconnect the blower motor control harness connector at the blower motor control processor.
- Test for less than 1.0 ohm of resistance between the ground circuit terminal A and ground.
- Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal C and ground.
- Connect a test lamp between the blower motor speed control circuit terminal B and the B+ circuit terminal C.
- Turn the blower motor ON high speed then OFF. The test lamp should turn ON and OFF when changing between the commanded states.
- Ignition OFF, Connect the harness connector at the blower motor control processor.
- Disconnect the blower harness connector at the blower motor.
- Ignition ON, verify that a test lamp illuminates between the blower motor supply voltage circuit terminal A and ground.
- Connect a test lamp between the blower motor supply voltage circuit terminal A and the blower motor ground circuit terminal B.
- Turn the blower motor ON high speed then to low speed. The test lamp light intensity should be bright when ON high speed and very dim or out when the blower is on low speed.
- If all circuits test normal, replace the blower motor.
| ⇒ | If greater than 1.0 ohm, 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 the test lamp is always ON, test the blower motor speed control circuit for a short to ground. If the circuit tests normal, replace the HVAC control module. |
| ⇒ | If the test lamp is always OFF, test the blower motor speed control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module. |
| ⇒ | If the test lamp does not illuminate, test the blower motor supply voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the blower motor control processor. |
| ⇒ | If the test lamp intensity is not correct, test the blower motor ground circuit terminal B for a short to voltage or an open/high resistance. If the circuit tests normal, replace the blower motor control processor. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
