U1591 – Vehicle Communication Bus Malfunction

The ODBII code U1591 indicates a malfunction in the vehicle communication bus, which affects the ability of various electronic control units (ECUs) to communicate with each other.

The severity of ODBII code U1591 is moderate.

Common Causes For: U1590 Lost Communication with the Body Control Module (BCM).

• Faulty wiring or connectors in the communication bus
• Malfunctioning control modules
• Corroded or damaged connectors
• Short circuits in the communication lines
• Open circuits in the communication lines
• Software issues or bugs in the control modules
• Incompatible aftermarket devices or modifications
• Poor ground connections
• Electrical interference from other components

Common misdiagnosis for U1591 U1591: “Vehicle Communication Bus Malfunction”

• Faulty Engine Control Module (ECM)
• Defective Body Control Module (BCM)
• Wiring issues or shorts in the communication bus
• Bad connectors or terminals
• Faulty sensors or actuators
• Issues with the powertrain control module (PCM)
• Problems with the diagnostic connector
• Software glitches or updates needed in the modules

Common Troubleshooting Steps

When dealing with OBD-II code U1591, which indicates a “Vehicle Communication Bus Malfunction,” 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. Sometimes, multiple codes can provide more context for the issue.
• Inspect the Wiring and Connectors: **Visual Inspection: Look for damaged, frayed, or corroded wiring and connectors related to the communication bus (CAN bus).
• **Connector Integrity: Ensure that all connectors are securely attached and free of corrosion or dirt.
• Check the Battery and Ground Connections: Ensure that the vehicle’s battery is in good condition and fully charged.
• Inspect ground connections for corrosion or looseness, as poor grounding can affect communication.
• Test the Communication Bus: Use a multimeter or an oscilloscope to check the voltage levels on the CAN bus wires. The typical voltage should be around 2.5V when the bus is idle.
• Look for any short circuits or open circuits in the communication lines.
• Inspect Modules: Check the various control modules (ECU, TCM, BCM, etc.) for proper operation. A malfunctioning module can disrupt communication.
• If possible, perform a software update on the modules, as outdated software can sometimes cause communication issues.
• Check for Interference: Look for any aftermarket devices or modifications that may interfere with the vehicle’s communication systems, such as alarms, remote starters, or audio systems.
• Perform a Network Test: If available, use a scan tool capable of performing a network test to check the communication between modules. This can help identify which module is not communicating properly.
• Clear Codes and Test Drive: After performing the above checks and repairs, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns.
• Consult Technical Service Bulletins (TSBs): Check for any TSBs related to U1591 for your specific vehicle make and model. Manufacturers may have specific fixes or recommendations for this code.
• Seek Professional Help: If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who has experience with your vehicle’s specific communication systems. By following these steps, you should be able to identify and resolve the underlying issue causing the U1591 code.