Diagnostic Routine J

Diagnostic Routine J

Diagnostic Overview

The Heating Ventilation Air Conditioning (HVAC) Module Does Not Respond To The Scan Tool

Refer to Wiring Diagram Set 14 for schematic and connector information Electrical Diagrams.

Refer to Wiring Diagram Set 54 for schematic and connector information Electrical Diagrams.

Refer to Wiring Diagram Set 55 for schematic and connector information Electrical Diagrams.

Normal Operation and Fault Conditions

The HVAC (Heating, Ventilation, and Air Conditioning) module communicates with the scan tool through the MS-CAN (Medium Speed Controller Area Network).

Visual Inspection and Diagnostic Pre-checks

Verify BCM (Body Control Module) fuse 46 (10A) is OK.

Pinpoint Test

1. CHECK THE MS-CAN (Medium Speed Controller Area Network) TERMINATION RESISTANCE

1. Ignition OFF.

2. Measure:





Is the resistance between 54 and 66 ohms?






2. CHECK THE MS-CAN (Medium Speed Controller Area Network) TERMINATION RESISTANCE WITH THE HVAC (Heating, Ventilation, and Air Conditioning) MODULE DISCONNECTED

1. Disconnect: HVAC (Heating, Ventilation, and Air Conditioning) Module C228A.

2. Measure:





Is the resistance between 108 and 132 ohms?






3. CHECK THE HVAC (Heating, Ventilation, and Air Conditioning) MODULE VOLTAGE SUPPLY CIRCUIT FOR AN OPEN

1. Disconnect: HVAC (Heating, Ventilation, and Air Conditioning) Module C228A.

2. Ignition ON.

3. Measure:





Is the voltage greater than 11 volts?






4. CHECK THE HVAC (Heating, Ventilation, and Air Conditioning) MODULE GROUND CIRCUIT FOR AN OPEN

1. Ignition OFF.

2. Measure:





Is the resistance less than 3 ohms?






5. CHECK THE MS-CAN (Medium Speed Controller Area Network) CIRCUITS BETWEEN THE HVAC (Heating, Ventilation, and Air Conditioning) MODULE AND THE DLC (Data Link Connector) FOR AN OPEN

1. Measure:





Are the resistances less than 3 ohms?






6. CHECK THE MS-CAN (Medium Speed Controller Area Network) CIRCUITS FOR A SHORT TO POWER

1. Connect: HVAC (Heating, Ventilation, and Air Conditioning) Module C228A.

2. Ignition ON.

3. Measure:









Is the voltage greater than 3 volts on either circuit?






7. CHECK THE MS-CAN (Medium Speed Controller Area Network) CIRCUITS FOR A SHORT TO GROUND

1. Ignition OFF.

2. Measure:





Are the resistances greater than 10,000 ohms?






8. CHECK FOR CORRECT HVAC (Heating, Ventilation, and Air Conditioning) MODULE OPERATION

1. Ignition OFF.

2. Disconnect and inspect the HVAC (Heating, Ventilation, and Air Conditioning) module connectors.

3. Repair:

- corrosion (replace connector or terminals- clean module pins)
- damaged or bent pins- replace terminals/pins
- pushed-out pins- replace pins as necessary

4. Reconnect the HVAC (Heating, Ventilation, and Air Conditioning) module connectors. Make sure they seat and latch correctly.

5. Operate the system and verify the concern is still present.

Is the concern still present?