U0140 – Lost Communication With Body Control Module

Quick Answer

• What it means: The car's computer has lost communication with the Body Control Module (BCM).
• Severity: Get towed or drive to a repair shop immediately. Essential vehicle functions may be compromised.
• Most common cause: A faulty BCM or a problem with the Controller Area Network (CAN) bus wiring.

What the U0140 Code Means

The U0140 diagnostic trouble code (DTC) officially stands for "Lost Communication With Body Control Module." In simpler terms, this means that one of your vehicle's primary control modules, typically the Powertrain Control Module (PCM) or Engine Control Module (ECM), is unable to communicate with the Body Control Module (BCM). The BCM is a crucial component responsible for managing a wide array of electronic functions within the vehicle, including power windows, door locks, interior and exterior lighting, security systems, and even some aspects of the charging system. When communication is lost, these functions can become inoperative, leading to significant drivability and safety concerns.

Common Symptoms

• Inoperative power windows, door locks, or mirrors
• Malfunctioning interior or exterior lights
• Security system issues (e.g., alarm not setting or car not starting)
• Intermittent or complete failure of gauges on the instrument cluster
• Problems with the charging system or battery drain
• Engine starting issues or no-start condition
• Warning lights illuminated on the dashboard (e.g., ABS, Airbag, Check Engine)

Common Causes

1. Faulty Body Control Module (BCM): The BCM itself can fail internally, leading to a complete loss of communication. This is a common and often costly culprit.
2. Wiring problems in the CAN bus: The Controller Area Network (CAN) bus is the communication network that allows various modules in your car to talk to each other. Open circuits, shorts to ground, or shorts to voltage in the CAN bus wiring between the PCM and BCM can disrupt communication.
3. Corroded or loose BCM connectors: Over time, the electrical connectors to the BCM can become corroded or loose, leading to intermittent or complete loss of communication.
4. Low battery voltage or faulty alternator: Insufficient voltage can cause modules to lose communication or malfunction. A weak battery or a failing alternator can be the root cause.
5. Faulty Powertrain Control Module (PCM)/Engine Control Module (ECM): While less common than a BCM failure, a faulty PCM or ECM can also be responsible for not being able to communicate with the BCM.
6. Software glitches: Rarely, a software anomaly or corruption within one of the control modules can cause communication issues.

How a Technician Diagnoses It

1. Verify the complaint and visual inspection: The technician will first confirm the symptoms and perform a thorough visual inspection for any obvious wiring damage, corrosion, or loose connections around the BCM, PCM, and associated harnesses.
2. Scan for all DTCs: A professional scan tool will be used to check all modules for communication U-codes and any other related fault codes, particularly in the BCM, PCM, ABS module, and instrument cluster.
3. Check battery voltage and charging system: The battery voltage will be checked with the engine off and running, and the alternator