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
--- | --- | --- | --- | ---
Stepper Motors 12 V Reference | B023A 02, B0223 06, B0233 06, B0408 06 | B0223 06, B0233 06, B0408 06 | -- | --
Air Temperature Actuator - Left Control 1 | B0408 06 | B0408 06 | B0408 01 | 1
Air Temperature Actuator - Left Control 2 | B0408 06 | B0408 06 | B0408 01 | 1
Air Temperature Actuator - Left Control 3 | B0408 06 | B0408 06 | B0408 01 | 1
Air Temperature Actuator - Left Control 4 | B0408 06 | B0408 06 | B0408 01 | 1
1. Air Temperature Malfunction

### Circuit/System Description

With the temperature switch at the HVAC control, the desired air temperature flap position can be put in. The selected value is passed to the HVAC control module via the LIN-Bus. The HVAC control module supplies a 12 V reference voltage to the stepper motor and energizes the 4 stepper motor coils with a pulsed ground signal. The stepper motor puts the mixed air flap into the calculated position, in order to reach the selected temperature.

### Diagnostic Aids

Check the following mechanical fault sources:

• | Air distribution box

• | Air distribution hoses/air distribution ducts

### Reference Information

#### Schematic Reference

HVAC Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Automatic HVAC 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, measure actual inside air temperature using a thermometer. Compare this value to the scan tool Passenger Compartment Air Temperature parameter. The measured temperature should be within 5°C (9°F) difference of parameter value.

⇒ | If not within the specified range, refer to DTC B0163 or B0183.

2. Measure actual temperature using a thermometer at each of the duct temperature sensors. Compare this value to the appropriate scan tool Duct Actual parameter. The measured temperature should be within 5°C (9°F) difference of appropriate Duct Actual parameter value.

⇒ | If not within the specified range, refer to DTC B0173, B0178, or B3933.

3. Measure actual evaporator temperature using a thermometer. Compare this value to the scan tool A/C Evaporator Temperature Sensor parameter. The measured temperature should be within 5°C (9°F) difference of parameter value.

⇒ | If not within the specified range, refer to DTC B0173, B0178, or B3933.

4. Observe the scan tool Sunload parameter. The reading should be between 50-1 150 W/m² and change with sunlight intensity.

⇒ | If not within the specified range or not change, refer to DTC B0163 or B0183.

5. Engine is running, activate and deactivate the A/C switch. Verify the A/C compressor can be activated and deactivated.

⇒ | If the A/C compressor cannot be activated or deactivated, refer to Air Conditioning Compressor Malfunction.

6. Verify the engine reaches its operating temperature.

### Circuit/System Testing

1. Ignition ON, turn the left temperature knob in all positions. Verify the scan tool Left Temperature Knob Position parameter. The reading should be between -5 to +5 and change with the knob position. At the left end position the reading should be 18 and at the right end position -18.

⇒ | If not the specified value, replace the A26 HVAC Control

2. If all circuits test normal, replace the M6L Air Temperature Actuator - Left and verify the M6L Air Temperature Actuator - Left can be put into all positions. If the M6L Air Temperature Actuator - Left cannot be put into all positions, replace the K33 HVAC Control Module.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Temperature Valve Actuator Replacement

• | Heater and Air Conditioning Control Replacement

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