For 1990-2009 cars

### 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
--- | --- | --- | --- | ---
Mode Aucuator 8-Volt Reference | 1 | 1 | 1 | --
Mode Aucuator Signal | 1 | 1 | 1 | --
Mode Aucuator Control A | 1 | 1 | 1 | --
Mode Aucuator Control B | 1 | 1 | 1 | --
Mode Aucuator Low Reference | -- | 1 | -- | --
1. Air Delivery Improper

### Circuit/System Description

The HVAC control module controls the HVAC door actuator to regulate the airflow through the HVAC system. The actuator consists of an electric motor and a potentiometer. The module supplies a low reference and 8-volt reference source voltage to the potentiometer. The HVAC control module monitors the voltage drop across the potentiometer on the door position signal circuit. When the actuator shaft rotates, the voltage on the door position signal circuit changes. The HVAC module controls the direction of the actuator door by changing the polarity of the control circuits.

### Diagnostic Aids

Inspect the Mode door actuator for the following:

• | A misaligned actuator

• | Broken or binding linkages or door

• | An obstruction that prevents the actuator from operating within the full range of motion

• | Missing seals to the door

### Reference Information

#### Schematic Reference

HVAC Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

• | Air Delivery Description and Operation

• | Air Temperature Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the mode actuator.
2. Test for less than 1 ohm between the low reference circuit terminal 1 and ground.

⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module.

3. Ignition ON, test for 7.8-8.2 volts between the 8-volt reference circuit terminal 3 and ground.

⇒ | If less than the specified range, test the 8-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

⇒ | If greater than the specified range, test the 8-volt reference circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.

4. Test for 7.8-8.2 volts between the signal circuit terminal 2 and ground.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.

⇒ | If less then specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

5. Connect a test lamp between control circuit terminal 4 and control circuit terminal 5.
6. Command the mode actuator door in both directions with the HVAC controls. The test lamp should turn ON and OFF when commanded in both directions.

⇒ | If the test lamp does not illuminate in both directions, test both control circuits for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

7. If all circuits test normal, test or replace the mode actuator.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heater and Air Conditioning Control Replacement

• | Defroster Valve Actuator Replacement