U1594 – Lost Communication with the Body Control Module (BCM) – Bus Off.

The ODBII code U1594 indicates that there is a loss of communication with the Body Control Module (BCM) due to a “Bus Off” condition, which typically means that the BCM is unable to communicate on the vehicle’s data bus, often due to a fault in the wiring, connectors, or the module itself.

The severity of ODBII code U1594 is generally considered moderate to severe.

Common Causes For: U1593 U1593: “Vehicle Communication Bus Malfunction”

• Faulty Body Control Module (BCM)
• Damaged wiring or connectors
• Short circuit in the communication lines
• Faulty or corroded ground connections
• Issues with the CAN bus system
• Malfunctioning other modules on the network
• Power supply issues to the BCM
• Software or firmware issues in the BCM

Common misdiagnosis for U1594 Lost Communication with the Body Control Module (BCM) – Bus Off.

• Faulty Body Control Module (BCM)
• Wiring issues or damaged connectors
• Faulty communication network (CAN bus)
• Power supply issues to the BCM
• Faulty or corroded ground connections
• Other module failures affecting communication
• Software or firmware issues in the BCM
• Incorrectly installed aftermarket accessories or modifications

Common Troubleshooting Steps

When dealing with OBD-II code U1594, which indicates “Lost Communication with the Body Control Module (BCM) – Bus Off,” there are several common troubleshooting steps you can follow to diagnose and potentially resolve the issue. Here’s a structured approach:

• Check for Additional Codes: Use an OBD-II scanner to check for any other trouble codes that may be present. This can provide more context and help identify related issues.
• 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 or corroded.
• Check the BCM: **Power and Ground: Verify that the BCM is receiving proper power and ground. Use a multimeter to check voltage at the BCM connector.
• **Module Functionality: If possible, test the BCM in another vehicle or replace it with a known good unit to see if the problem persists.
• Inspect the CAN Bus: **Bus Communication: The BCM communicates over the Controller Area Network (CAN) bus. Check for continuity and proper voltage levels on the CAN bus wires.
• **Termination Resistors: Ensure that the CAN bus has the correct termination resistors in place and that they are functioning properly.
• Check for Short Circuits: Use a multimeter to check for short circuits in the wiring that could be causing communication issues.
• Scan for Communication Issues: Use a professional scan tool to monitor the communication on the CAN bus. Look for any irregularities or interruptions in communication between modules.
• Inspect Other Modules: If other modules on the CAN bus are malfunctioning, they can cause communication issues with the BCM. Check the functionality of other modules that communicate with the BCM.
• Software Updates: Check if there are any software updates available for the BCM or other related modules. Sometimes, manufacturers release updates to fix known communication issues.
• Clear Codes and Test Drive: After performing any repairs or checks, clear the trouble codes and take the vehicle for a test drive to see if the code reappears.
• Consult Technical Service Bulletins (TSBs): Look for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued guidance on common issues related to the BCM and communication errors.1
• Professional Diagnosis: If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership with experience in diagnosing BCM and communication issues. By following these steps, you should be able to identify the root cause of the U1594 code and take appropriate action to resolve the issue.