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

### Circuit/System Description

The actuators operate by using XXX circuits: a XXX-volt reference, low reference, signal circuit and two bi-directional 0 or XXX-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. When the HVAC control module detects, from the feedback potentiometer, that the actuator is in the desired position, both circuits are set to 0 volts. The HVAC control module switches the appropriate control circuit to 12 volts, in order to move the actuator.

### Diagnostic Aids

Check the mode door and the mode actuator for the following conditions:

• | A misaligned mode actuator

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

• | Missing seals to the mode door

• | Broken or binding linkages or mode door

• | Misaligned seals to the mode door

### Reference Information

#### Schematic Reference

• | HVAC Schematics for the automatic system

• | HVAC Schematics for the manual system

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

• | For air temperature description and operation refer to LINK.

• | Air Delivery Description and Operation for the automatic system.

• | Air Delivery Description and Operation for the manual system.

#### 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 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 10 and ground.

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

3. Ignition ON, test for XXX or XXX-volts between the 5-volt reference circuit terminal XXX and ground.

• | If less than the specified range, test the XXX-volt reference circuit for a short to ground or an open/high resistance.

• | If greater than the specified range, test the XXX-volt reference circuit for a short to voltage.

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

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

5. Install a 3A fused jumper wire between the signal circuit terminal XXX and the low reference circuit terminal XXX. 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 XXX 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 XXX 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 XXX and control circuit terminal XXX.
9. Command the appropriate actuator door in both directions. The test lamp should turn ON and OFF when moved 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

After completing the diagnostic procedure perform the diagnostic repair verification. Refer to Diagnostic Repair Verification.

• | Refer to Mode Control Cam Replacement.

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