U1242 – Lost Communication with Body Control Module (BCM).

The ODBII code U1242 indicates that there is a loss of communication between the vehicle’s diagnostic system and the Body Control Module (BCM), which may affect various electrical functions and systems in the vehicle.

The severity of ODBII code U1242 is generally considered moderate to severe, as it indicates a communication issue that can affect multiple systems in the vehicle.

Common Causes For: U1241 SCP (J1850) Invalid or Missing Data for Primary Id

• Faulty Body Control Module (BCM)
• Damaged wiring or connectors
• Corroded terminals
• Blown fuses
• Poor ground connections
• Software issues or programming errors
• Intermittent electrical connections
• Malfunctioning sensors or components connected to the BCM

Common misdiagnosis for U1242 Lost Communication with Body Control Module (BCM)”.

• Faulty Body Control Module (BCM)
• Wiring issues or damaged connectors
• Faulty Instrument Cluster
• Malfunctioning Powertrain Control Module (PCM)
• Battery or charging system problems
• Corroded ground connections
• Faulty communication lines (CAN bus issues)
• Software or firmware issues in the BCM or other modules

Common Troubleshooting Steps

When dealing with the OBD-II code U1242, which indicates “Lost Communication with Body Control Module (BCM),” there are several common troubleshooting steps you can follow to diagnose and potentially resolve the issue. Here’s a structured approach:

• Check for Other Codes: Use an OBD-II scanner to check for any additional trouble codes. Sometimes, multiple codes can provide more context about the issue.
• Inspect the Wiring and Connectors: **Visual Inspection: Check the wiring harness and connectors related to the BCM for any signs of damage, corrosion, or loose connections.
• **Connector Pins: Ensure that the pins in the connectors are not bent, corroded, or pushed back.
• Check Power and Ground: **Power Supply: Verify that the BCM is receiving the correct voltage. Use a multimeter to check the power supply to the BCM.
• **Ground Connections: Ensure that the ground connections for the BCM are secure and free of corrosion.
• Inspect the BCM: **Physical Condition: Check the BCM for any signs of physical damage or water intrusion.
• **Reprogramming: If the BCM has been replaced, ensure that it has been properly programmed to the vehicle.
• Test Communication Lines: **CAN Bus: Use a scan tool to check the communication on the CAN bus. If other modules are not communicating, the issue may be with the bus itself.
• **Scope Testing: If available, use an oscilloscope to check for proper signal patterns on the communication lines.
• Check for Intermittent Issues: **Temperature Sensitivity: Sometimes, issues can be temperature-related. Monitor the vehicle to see if the problem occurs under specific conditions (e.g., after the vehicle warms up).
• **Vibration: Check if the issue occurs when the vehicle is in motion or over bumps.
• Inspect Related Modules: If the BCM is not communicating, check other modules that may be connected to the same communication network. A fault in one module can affect communication with others.
• Perform a Hard Reset: Disconnect the vehicle’s battery for a few minutes to reset the BCM and other modules. Reconnect and see if the code reappears.
• Consult Technical Service Bulletins (TSBs): Check for any manufacturer-specific TSBs related to the U1242 code or BCM issues. There may be known fixes or recalls.
• Replace the BCM (if necessary): If all other troubleshooting steps fail and the BCM is determined to be faulty, consider replacing it. Ensure proper programming and configuration after replacement.1
• Seek Professional Help: If you are unable to resolve the issue, it may be best to consult a professional mechanic or dealership with experience in diagnosing and repairing BCM-related issues. By following these steps, you should be able to identify the root cause of the U1242 code and take appropriate action to resolve it.