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
--- | --- | --- | --- | ---
5-Volt Reference | 1 | 1 | 1 | --
Auxiliary Mode Door Signal | 2 | 2 | 2 | --
Auxiliary Air Temperature Door Signal | 3 | 3 | 3 | --
Auxiliary Blower Speed Signal | 4 | 4 | 4 | --
Low Reference | -- | 1 | -- | --
1. Auxiliary HVAC Control Assembly Inoperative 2. Auxiliary Mode Door Malfunction 3. Auxiliary Air Temperature Malfunction 4. Auxiliary Blower Speed Malfunction

### Circuit/System Description

The auxiliary HVAC control assembly is an input to the primary HVAC control module. The primary HVAC control module uses a low reference circuit and a 5-volt reference circuit to determine the position of the auxiliary HVAC control switches. The auxiliary HVAC assembly has 3 signal circuits to relay the desired mode, temperature and blower motor speeds to the primary HVAC control module. The primary HVAC control module uses this input to adjust the desired positions of the mode, temperature and blower motor.

### 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

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition ON, verify DTC B0433 or B3782 is not set.

⇒ | If either of the DTCs are set, refer to DTC B0228, B0413, B0423, B0433, B3779, or B3782 (RPO CJ2) or DTC B0228, B0413, B0433, B3779, or B3782 (RPO C67 or CJ3).

2. Individually adjust each of the controls on the auxiliary HVAC control assembly. Verify that the auxiliary blower motor, temperature actuator and Mode actuator move properly to the selected positions or desired speeds.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the auxiliary HVAC control assembly.
2. Ignition OFF, test for less than 1 ohm between the low reference circuit terminal 4 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 3 and ground.

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

⇒ | If less than the specified range, test the 5-volt reference circuit for an short to ground or an open/high resistance.

4. Ignition OFF, connect the harness connector at the auxiliary HVAC control assembly. Disconnect the X2 harness connector at the HVAC control module.
5. Ignition ON, verify voltage at the signal circuit terminal 19 varies between 0.5-4.5 volts while varying the auxiliary blower speed from low to high.

⇒ | If not within the specified range, test the signal circuit for a short to voltage, a short to ground, or an open/high resistance. If the circuit tests normal, test or replace the auxiliary HVAC control assembly.

6. Verify voltage at the signal circuit terminal 8 varies between 0.5-4.5 volts while varying the auxiliary temperature setting from warm to cool.

⇒ | If not within the specified range, test the signal circuit for a short to voltage, a short to ground, or an open/high resistance. If the circuit tests normal, test or replace the auxiliary HVAC control assembly.

7. Verify voltage at the signal circuit terminal 9 varies between 0.5-4.5 volts while selecting the three mode positions.

⇒ | If not within the specified range, test the signal circuit for a short to voltage, a short to ground, or an open/high resistance. If the circuit tests normal, test or replace the auxiliary HVAC control assembly.

8. Ignition OFF, connect the X2 harness connector at the HVAC control module.
9. Ignition ON, verify the auxiliary blower motor speed changes while varying the blower speed setting on the auxiliary HVAC control assembly.

⇒ | If the blower speed does not vary, refer to Auxiliary Blower Motor Malfunction (RPO CJ2) or Auxiliary Blower Motor Malfunction (RPO C67 or CJ3).

10. If all circuits test normal, replace the HVAC control module.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Auxiliary Heater and Air Conditioning Control Module Replacement

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