U0142 Lost Communication With Body Control Module "B"

Introduction:

The U0142 diagnostic trouble code (DTC) indicates a loss of communication with the Body Control Module "B" (BCM-B) on a vehicle's Controller Area Network (CAN) bus. This means that other modules on the network, such as the Engine Control Module (ECM), Transmission Control Module (TCM), or Anti-lock Braking System (ABS), are no longer able to communicate with the BCM-B. This communication breakdown can lead to a variety of symptoms and potentially affect numerous vehicle functions.

Table: U0142 Lost Communication With Body Control Module "B"

Detailed Explanations:

Definition: U0142: Lost Communication With Body Control Module "B"

This DTC signifies that the BCM-B is not communicating properly with other modules on the vehicle's Controller Area Network (CAN) bus. The CAN bus is a network that allows different electronic control units (ECUs) in the vehicle to communicate with each other. The BCM-B is a critical module that controls many body-related functions.

Symptoms:

The symptoms of a U0142 code can vary widely depending on the specific functions controlled by the BCM-B in the affected vehicle. Common symptoms include:

• Malfunctioning or inoperative vehicle systems: This could include issues with lights (headlights, taillights, interior lights), wipers, power windows, power door locks, and other body-related functions.
• Warning lights illuminated on the dashboard: The Check Engine light (CEL), ABS light, or other warning lights may illuminate, indicating a problem with the vehicle's systems.
• Vehicle starting problems: In some cases, a communication issue with the BCM-B can prevent the vehicle from starting.
• Erratic behavior of electrical components: This could include intermittent operation of various electrical components or unexpected behavior.
• Diagnostic trouble codes (DTCs) in other modules related to BCM functions: Other modules that rely on communication with the BCM-B may also store DTCs related to the lost communication.

Common Causes:

Several factors can contribute to a U0142 code:

• Faulty BCM-B: The BCM-B itself may have failed internally. This is often the most expensive and complex cause to resolve.
• CAN Bus Issues: Problems within the CAN bus wiring, such as opens (broken wires), shorts (wires touching), or high resistance (corroded connections), can disrupt communication.
• Wiring Issues: Damaged, corroded, or loose wiring or connectors connected to the BCM-B can interrupt power, ground, or communication signals.
• Power Supply Issues: The BCM-B may not be receiving adequate power due to a faulty power supply circuit.
• Ground Issues: A poor or missing ground connection can prevent the BCM-B from functioning correctly.
• Other Modules: A malfunctioning module on the CAN bus can sometimes interfere with communication between other modules, including the BCM-B.
• Software Issues: Software corruption or incompatibility in the BCM-B or other modules can cause communication problems.
• Blown Fuse: A blown fuse in the BCM-B power supply circuit can cut off power to the module.

Diagnostic Steps:

A systematic approach is crucial for diagnosing a U0142 code:

1. Verify the DTC with a scan tool: Confirm that the U0142 code is present.
2. Check for other DTCs in other modules: Look for other DTCs in other modules that might be related to the BCM-B or the CAN bus.
3. Inspect the BCM-B and related wiring for damage: Visually inspect the BCM-B and its wiring harness for any signs of damage, corrosion, or loose connections.
4. Check the BCM-B power and ground circuits: Use a multimeter to verify that the BCM-B is receiving the correct voltage and has a good ground connection.
5. Test the CAN bus integrity with an oscilloscope or CAN bus tester: This is a critical step to identify problems within the CAN bus wiring. An oscilloscope can display the CAN bus waveforms, allowing you to identify signal abnormalities. A CAN bus tester can also be used to check the bus's electrical characteristics.
6. Check for water intrusion or corrosion: Inspect the BCM-B and its connectors for signs of water intrusion or corrosion, which can damage electrical components.
7. Inspect all connectors for damage and corrosion: Carefully examine all connectors connected to the BCM-B and the CAN bus for damage, corrosion, or loose pins.
8. Check for loose or damaged pins in the connectors: Ensure that all pins in the connectors are securely seated and not damaged.
9. Check the BCM-B fuse: Verify that the fuse for the BCM-B is not blown.
10. Check the BCM-B for software updates: Check with the manufacturer to see if there are any software updates available for the BCM-B.
11. Check the BCM-B resistance: Check the resistance of the BCM-B itself to make sure it is within the specified range.

Repair Strategies:

The repair strategy will depend on the underlying cause of the U0142 code:

• Repair or replace damaged wiring or connectors: If damaged wiring or connectors are found, repair or replace them as needed.
• Repair or replace faulty ground connections: Ensure that the BCM-B has a good ground connection. Clean and tighten any corroded ground connections.
• Replace blown fuses: Replace any blown fuses with the correct amperage rating.
• Reprogram or replace the BCM-B: If the BCM-B is faulty, it may need to be reprogrammed or replaced. This often requires specialized equipment and expertise.
• Repair or replace faulty CAN bus wiring: Repair any damaged CAN bus wiring, ensuring that the correct wire gauge and shielding are used.
• Diagnose and repair any other modules causing CAN bus interference: If another module is interfering with CAN bus communication, diagnose and repair or replace that module.

Severity:

The severity of a U0142 code can range from moderate to high, depending on the functions controlled by the BCM-B in the affected vehicle. If the BCM-B controls critical safety systems, such as the airbags or ABS, the code can pose a significant safety risk.

Related Codes:

Several other DTCs may be related to a U0142 code, indicating communication problems with other modules on the CAN bus:

• U0100 (Lost Communication With ECM/PCM)
• U0101 (Lost Communication With TCM)
• U0121 (Lost Communication With ABS Control Module)
• U0155 (Lost Communication With Instrument Panel Cluster (IPC) Control Module)

Tools Required:

Diagnosing and repairing a U0142 code typically requires the following tools:

• Scan tool with CAN bus diagnostic capabilities
• Multimeter
• Oscilloscope (optional, but highly recommended for CAN bus testing)
• Wiring diagrams for the specific vehicle
• Basic hand tools
• Connector test kit

Cost of Repair:

The cost of repairing a U0142 code can vary significantly depending on the cause. Simple wiring repairs might cost $50-$200. BCM-B replacement can range from $300 to $1000 or more, including parts and labor. CAN bus diagnostics can also add to the cost, as it can be a time-consuming process.

Preventative Measures:

Several preventative measures can help reduce the risk of a U0142 code:

• Regular vehicle maintenance
• Promptly address any electrical issues
• Protect wiring from damage
• Avoid modifications that could interfere with the CAN bus
• Ensure proper grounding

Location of BCM-B:

The location of the BCM-B varies depending on the vehicle make and model. It is typically located under the dashboard, in the center console, or in the engine compartment. Consult the vehicle's service manual for the exact location.

Testing CAN Bus:

CAN bus testing involves checking the resistance and voltage levels on the CAN High and CAN Low wires. An oscilloscope can be used to visualize the CAN bus waveforms and identify communication problems. Proper termination resistance (typically 120 ohms) between CAN High and CAN Low should be verified. Voltage levels should be within the manufacturer's specifications.

BCM-B Functionality:

The BCM-B controls various body functions, including lighting, power windows, power door locks, remote keyless entry, wipers, and interior accessories. It also acts as a gateway for communication between different modules on the CAN bus. It often manages security features and comfort systems within the vehicle.

Frequently Asked Questions:

• What does the U0142 code mean? It indicates a loss of communication with the Body Control Module "B" on the vehicle's CAN bus. This means other modules can't communicate with the BCM-B.

• Can I drive my car with a U0142 code? It depends on the severity of the symptoms. If critical systems are affected, driving may be unsafe. It's best to get it checked by a professional.

• How do I fix a U0142 code? The fix depends on the cause, ranging from simple wiring repairs to BCM-B replacement. Diagnosis is essential.

• Is U0142 an expensive repair? It can be, especially if the BCM-B needs to be replaced. Wiring repairs are typically less costly.

• Can a bad battery cause a U0142 code? A weak or failing battery can sometimes cause communication issues on the CAN bus, potentially leading to a U0142 code.

Conclusion:

The U0142 code signifies a communication breakdown with the BCM-B, which can lead to various vehicle malfunctions. A thorough diagnostic process is crucial to identify the root cause, and repair strategies should be tailored accordingly to restore proper communication and vehicle functionality.