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
--- | --- | --- | --- | ---
Air Temperature Door Control A | 1 | 1 | 1 | --
Air Temperature Door Control B | 1 | 1 | 1 | --
5-Volt Reference | 1 | 1 | 1 | --
Air Temperature Door Position Signal | -- | 1 | 1 | --
Air Temperature Actuator Low Reference | -- | 1 | 1 | --
1. Air Temperature Actuator Inoperative

### Circuit/System Description

The actuators operate using 5 circuits. A 5-volt reference, low reference, signal circuit and two bi-directional 0 or 12 volt control circuits. The HVAC control module supplies a low reference and 5-volt reference to the potentiometer. The HVAC control module monitors the voltage drop across the potentiometer on the door position signal circuit. As the actuator door changes position the door position signal circuit voltage also changes. The two bi-directional control circuits enable the actuator to operate. Both circuits are set to 0 volts when the HVAC control module detects, from the feedback potentiometer, that the actuator is in the desired position. In order to move the actuator, the HVAC control module switches the appropriate control circuit to 12 volts.

### Diagnostic Aids

Inspect the air temperature door and the air temperature actuator for the following conditions:

• | A misaligned air temperature actuator

• | Broken or binding linkages or air temperature door

• | An obstruction that prevents the air temperature door from operating within its full range of motion

• | Missing seals to the air temperature door

• | Misaligned seals to the air temperature door

### Reference Information

#### Schematic Reference

HVAC Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

• | Air Temperature Description and Operation

• | Air Delivery Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

Ignition ON, move the mode switch from defrost to floor the mode door should match the selected position.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the appropriate actuator.
2. Ignition OFF, test for less than 10 ohms between the low reference circuit terminal 7 and ground.

⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance.

3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 10 and ground.

⇒ | If less than the specified range, test the 5-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 5-volt reference circuit for a short to voltage.

4. Using a DVOM verify the voltage on the signal circuit is greater than 4.8 volts.

⇒ | If less than the specified range, test the signal circuit terminal 9 for a short to ground.

5. Install a 3A fused jumper wire between the signal circuit terminal 9 and the low reference circuit terminal 10. Using a DVOM verify the voltage on the signal circuit is greater than 0.2 volts.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance.

6. Ignition OFF, test for less than 10 ohms between the control circuit terminal 6 and ground.

⇒ | If greater than the specified range, test the control circuit for a short to voltage or an open/high resistance.

7. Ignition OFF, test for less than 10 ohms between the control circuit terminal 5 and ground.

⇒ | If greater than the specified range, test the control circuit for a short to voltage or an open/high resistance.

8. Connect a test lamp between control circuit terminal 5 and control circuit terminal 6.
9. Command the appropriate actuator door in both directions. The test lamp should turn ON and OFF when commanded in both directions.

⇒ | If the test lamp remains OFF during either of the commands, test for a short to ground on either control circuit. If the circuits test normal, replace the HVAC control module.

10. If both circuits test normal, test or replace the actuator.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Temperature Valve Actuator Replacement

• | Control Module References for HVAC control module replacement, setup, and programming