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, B0233 06, B022A 06, B0223 06, B0408 06,

B0418 06

B0233 06,

B022A 06,

B0223 06,

B0408 06,

B0418 06

--

--

Mode Actuator Control 1 | B0233 06 | B0233 06 | B0233 01 | 1
Mode Actuator Control 2 | B0233 06 | B0233 06 | B0233 01 | 1
Mode Actuator Control 3 | B0233 06 | B0233 06 | B0233 01 | 1
Mode Actuator Control 4 | B0233 06 | B0233 06 | B0233 01 | 1
1. Air Distribution Malfunction

### Circuit/System Description

With the defrost switch, air to foot well switch, air to windscreen switch and the air to head area switch at the HVAC control, the wished air distribution flap position can be put in. The selected value is passed over the LIN-Bus to the HVAC control module. 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 air distribution flap into the selected position.

### Diagnostic Aids

Check the following mechanical fault sources:

• | Air distribution box

• | Air distribution hoses/air distributing 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 Testing

1. Ignition ON, press and release the switch for air distribution to head. Verify the scan tool Front Defrost Switch parameter changes between Active and Inactive.

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

2. Press and release the switch for air distribution to face. Verify the scan tool Instrument Panel Vents switch parameter changes between Active and Inactive.

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

3. Press and release the switch for air distribution to floor. Verify the scan tool Floor Mode Switch parameter changes between Active and Inactive.

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

4. Press and release the defrost switch. Verify the scan tool Enhanced Defrost Switch parameter changes between Active and Inactive.

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

5. If all circuits test normal, replace the M37 Mode Actuator and verify the M37 Mode Actuator can be put into all positions. If the M37 Mode Actuator cannot be put into all positions, replace the K33 HVAC Control Module.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heater and Air Conditioning Control Replacement

• | Mode Control Cam Actuator Replacement

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