For 1990-2009 cars only
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 |
|---|---|---|---|---|
Rear Blower Motor Speed Control | 2 | 2 | 2 | -- |
Aux. Blower Motor Control Module Ground | -- | 2 | -- | -- |
Blower Speed Feed Back Signal | 2 | 2 | 2 | -- |
Auxiliary Blower Motor Low Reference | 1 | 2 | 2 | -- |
Auxiliary Blower Motor Ground | -- | 2 | 2 | -- |
Auxiliary Blower Motor B+ | 2 | 2 | -- | -- |
1. Always ON 2. Inoperative | ||||
Circuit/System Description
Auxiliary HVAC Control Module
The front HVAC control module must be in the ON position for GMLAN communication to allow the rear HVAC control module to operate.
Auxiliary Blower Motor Control Module
The following are auxiliary blower motor control module circuits:
| • | Rear blower motor speed control circuit--When the auxiliary blower switch is placed in any speed position this circuit is a pulse width modulated signal that is sent from the Auxiliary HVAC control module to the auxiliary blower motor control module. |
| • | Ground--A constant body ground is supplied to the auxiliary blower motor control module. |
| • | Low reference--This circuit is grounded through the auxiliary blower motor control module only when the auxiliary HVAC control module is in high speed. In all other blower speeds this circuit is a pulse width modulated signal (PWM). The longer this circuit is pulsed the ground the faster the blower speed will be. |
| • | Blower speed feed back signal--This feedback circuit displays in percent on the TECH 2 the commanded output blower speed that the auxiliary blower motor control module is sending to the auxiliary blower motor. |
Auxiliary Blower Motor
The following are auxiliary blower motor circuits:
| • | Ground--A constant body ground is supplied the blower motor. |
| • | Ignition voltage--Ignition voltage is supplied to the blower motor from the rear fuse box. |
| • | Low reference--This circuit is grounded through the auxiliary blower motor control module only when the auxiliary HVAC control module is in high speed. In all other blower speeds this circuit is a pulse width modulated signal (PWM). The longer this circuit is pulsed the ground the faster the blower speed will be. |
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 auxiliary blower motor.
- Test for less than 1 ohm of resistance between the ground circuit terminal 2 and ground.
- Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 1 and ground.
- Ignition OFF, disconnect the harness connector at the auxiliary blower motor control module.
- Ignition ON, verify that a test lamp does not illuminates between the control circuit terminal 4 and ground.
- Test for less than 1 ohm of resistance between the ground circuit terminal 2 and ground.
- Connect the auxiliary blower motor connector.
- Ignition ON, verity that a test lamp illuminates between the control circuit terminal 4 and ground.
- Select the AUTO position on the front HVAC module.
- Test for 12-27 Mv between the control circuit terminal 1 and ground while adjusting the rear auxiliary HVAC control module blower from 1 to 4 bars.
- Test for above 10 volts while adjusting the rear auxiliary HVAC blower switch to 5 bars.
- Select the AUTO position on the rear auxiliary HVAC control module.
- Test for 12-145 Mv between the control circuit terminal 1 and ground while adjusting the front HVAC control module blower from low speed to high speed.
- Place the front and rear HVAC modules in low speed.
- Test for 0.2--15 Mv between the signal circuit terminal 3 and ground.
- If all circuits test normal, replace the auxiliary blower motor control module.
| ⇒ | If greater than 1 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 aux blower motor. |
| ⇒ | If test lamp illuminates, test the control circuit for a short to voltage. |
| ⇒ | If greater than 1 ohm, test the ground circuit for an open/high resistance. |
| ⇒ | If test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance. If circuit test normal replace auxiliary blower motor. |
| ⇒ | If less than 12 Mv, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal replace the rear auxiliary HVAC module. |
| ⇒ | If greater than 27 Mv, test the control circuit for a short to voltage. If the circuit tests normal replace the rear auxiliary HVAC module. |
| ⇒ | If less than 10 volts replace the rear auxiliary HVAC control module. |
| ⇒ | If less than 12 Mv, replace the front HVAC control module. |
| ⇒ | If greater than 145 Mv, replace the front HVAC control module. |
| ⇒ | If less than 0.2 Mv, test the signal circuit for a short to ground or an open high resistance. If the circuit tests normal replace the rear auxiliary HVAC module. |
| ⇒ | If greater than 15 Mv, test the signal circuit for a short to voltage. If the circuit tests normal replace the rear auxiliary HVAC module. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for HVAC Control Module or Auxiliary HVAC replacement, setup and programming |
